Virtualization - Aug 2016 - [RFC/PATCHSET 0/3] virtio: Implement virtio pstore device (v4)

Hello,

This is another iteration of the virtio-pstore work.  I've addressed
all comments from Daniel Berrange on the qemu side.

 * changes in v4)
  - use qio_channel_file_new_path()  (Daniel)
  - rename to delete_old_pstore_file  (Daniel)
  - convert G_REMOVE_SOURCE to FALSE  (Daniel)

 * changes in v3)
  - use QIOChannel API  (Stefan, Daniel)
  - add bound check for malcious guests  (Daniel)
  - drop support PSTORE_TYPE_CONSOLE for now
  - update license to allow GPL v2 or later  (Michael)
  - limit number of pstore files on qemu

 * changes in v2)
  - update VIRTIO_ID_PSTORE to 22  (Cornelia, Stefan)
  - make buffer size configurable  (Cornelia)
  - support PSTORE_TYPE_CONSOLE  (Kees)
  - use separate virtqueues for read and write
  - support concurrent async write
  - manage pstore (file) id in device side
  - fix various mistakes in qemu device  (Stefan)

It started from the fact that dumping ftrace buffer at kernel
oops/panic takes too much time.  Although there's a way to reduce the
size of the original data, sometimes I want to have the information as
many as possible.  Maybe kexec/kdump can solve this problem but it
consumes some portion of guest memory so I'd like to avoid it.  And I
know the qemu + crashtool can dump and analyze the whole guest memory
including the ftrace buffer without wasting guest memory, but it adds
one more layer and has some limitation as an out-of-tree tool like not
being in sync with the kernel changes.

So I think it'd be great using the pstore interface to dump guest
kernel data on the host.  One can read the data on the host directly
or on the guest (at the next boot) using pstore filesystem as usual.
While this patchset only implements dumping kernel log buffer, it can
be extended to have ftrace buffer and probably some more..

The patch 0001 implements virtio pstore driver.  It has two virt queue
for (sync) read and (async) write, pstore buffer and io request and
response structure.  The virtio_pstore_req struct is to give
information about the current pstore operation.  The result will be
written to the virtio_pstore_res struct.  For read operation it also
uses virtio_pstore_fileinfo struct.

The patch 0002 and 0003 implement virtio-pstore legacy PCI device on
qemu-kvm and kvmtool respectively.  I referenced virtio-baloon and
virtio-rng implementations and I don't know whether kvmtool supports
modern virtio 1.0+ spec.  Other transports might be supported later.

For example, using virtio-pstore on qemu looks like below:

  $ qemu-system-x86_64 -enable-kvm -device virtio-pstore,directory=xxx

When guest kernel gets panic the log messages will be saved under the
xxx directory.

  $ ls xxx
  dmesg-1.enc.z  dmesg-2.enc.z

As you can see the pstore subsystem compresses the log data using zlib
(now supports lzo and lz4 too).  The data can be extracted with the
following command:

  $ cat xxx/dmesg-1.enc.z | \
  > python -c 'import sys, zlib;
print(zlib.decompress(sys.stdin.read()))'
  Oops#1 Part1
  <5>[    0.000000] Linux version 4.6.0kvm+ (namhyung at danjae) (gcc
version 5.3.0 (GCC) ) #145 SMP Mon Jul 18 10:22:45 KST 2016
  <6>[    0.000000] Command line: root=/dev/vda console=ttyS0
  <6>[    0.000000] x86/fpu: Legacy x87 FPU detected.
  <6>[    0.000000] x86/fpu: Using 'eager' FPU context switches.
  <6>[    0.000000] e820: BIOS-provided physical RAM map:
  <6>[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff]
usable
  <6>[    0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff]
reserved
  <6>[    0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff]
reserved
  <6>[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000007fddfff]
usable
  <6>[    0.000000] BIOS-e820: [mem 0x0000000007fde000-0x0000000007ffffff]
reserved
  <6>[    0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff]
reserved
  <6>[    0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff]
reserved
  <6>[    0.000000] NX (Execute Disable) protection: active
  <6>[    0.000000] SMBIOS 2.8 present.
  <7>[    0.000000] DMI: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014
  ...


Namhyung Kim (3):
  virtio: Basic implementation of virtio pstore driver
  qemu: Implement virtio-pstore device
  kvmtool: Implement virtio-pstore device


 drivers/virtio/Kconfig             |  10 +
 drivers/virtio/Makefile            |   1 +
 drivers/virtio/virtio_pstore.c     | 417 +++++++++++++++++++++++++++++++++++++
 include/uapi/linux/Kbuild          |   1 +
 include/uapi/linux/virtio_ids.h    |   1 +
 include/uapi/linux/virtio_pstore.h |  74 +++++++
 6 files changed, 504 insertions(+)
 create mode 100644 drivers/virtio/virtio_pstore.c
 create mode 100644 include/uapi/linux/virtio_pstore.h


Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Radim Kr?m?? <rkrcmar at redhat.com>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: Anthony Liguori <aliguori at amazon.com>
Cc: Anton Vorontsov <anton at enomsg.org>
Cc: Colin Cross <ccross at android.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Tony Luck <tony.luck at intel.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Minchan Kim <minchan at kernel.org>
Cc: Will Deacon <will.deacon at arm.com>
Cc: kvm at vger.kernel.org
Cc: qemu-devel at nongnu.org
Cc: virtualization at lists.linux-foundation.org
Cc: virtio-dev at lists.oasis-open.org
Thanks,
Namhyung


-- 
2.9.3

The virtio pstore driver provides interface to the pstore subsystem so
that the guest kernel's log/dump message can be saved on the host
machine.  Users can access the log file directly on the host, or on the
guest at the next boot using pstore filesystem.  It currently deals with
kernel log (printk) buffer only, but we can extend it to have other
information (like ftrace dump) later.

It supports legacy PCI device using single order-2 page buffer.  It uses
two virtqueues - one for (sync) read and another for (async) write.
Since it cannot wait for write finished, it supports up to 128
concurrent IO.  The buffer size is configurable now.

Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Radim Kr?m?? <rkrcmar at redhat.com>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: Anthony Liguori <aliguori at amazon.com>
Cc: Anton Vorontsov <anton at enomsg.org>
Cc: Colin Cross <ccross at android.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Tony Luck <tony.luck at intel.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Minchan Kim <minchan at kernel.org>
Cc: Will Deacon <will.deacon at arm.com>
Cc: kvm at vger.kernel.org
Cc: qemu-devel at nongnu.org
Cc: virtualization at lists.linux-foundation.org
Cc: virtio-dev at lists.oasis-open.org
Signed-off-by: Namhyung Kim <namhyung at kernel.org>
---
 drivers/virtio/Kconfig             |  10 +
 drivers/virtio/Makefile            |   1 +
 drivers/virtio/virtio_pstore.c     | 417 +++++++++++++++++++++++++++++++++++++
 include/uapi/linux/Kbuild          |   1 +
 include/uapi/linux/virtio_ids.h    |   1 +
 include/uapi/linux/virtio_pstore.h |  74 +++++++
 6 files changed, 504 insertions(+)
 create mode 100644 drivers/virtio/virtio_pstore.c
 create mode 100644 include/uapi/linux/virtio_pstore.h

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 77590320d44c..8f0e6c796c12 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -58,6 +58,16 @@ config VIRTIO_INPUT
 
 	 If unsure, say M.
 
+config VIRTIO_PSTORE
+	tristate "Virtio pstore driver"
+	depends on VIRTIO
+	depends on PSTORE
+	---help---
+	 This driver supports virtio pstore devices to save/restore
+	 panic and oops messages on the host.
+
+	 If unsure, say M.
+
  config VIRTIO_MMIO
 	tristate "Platform bus driver for memory mapped virtio devices"
 	depends on HAS_IOMEM && HAS_DMA
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 41e30e3dc842..bee68cb26d48 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -5,3 +5,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
 virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
 obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
 obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
+obj-$(CONFIG_VIRTIO_PSTORE) += virtio_pstore.o
diff --git a/drivers/virtio/virtio_pstore.c b/drivers/virtio/virtio_pstore.c
new file mode 100644
index 000000000000..ec41f0d2f0b7
--- /dev/null
+++ b/drivers/virtio/virtio_pstore.c
@@ -0,0 +1,417 @@
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/pstore.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_pstore.h>
+
+#define VIRT_PSTORE_ORDER    2
+#define VIRT_PSTORE_BUFSIZE  (4096 << VIRT_PSTORE_ORDER)
+#define VIRT_PSTORE_NR_REQ   128
+
+struct virtio_pstore {
+	struct virtio_device	*vdev;
+	struct virtqueue	*vq[2];
+	struct pstore_info	 pstore;
+	struct virtio_pstore_req req[VIRT_PSTORE_NR_REQ];
+	struct virtio_pstore_res res[VIRT_PSTORE_NR_REQ];
+	unsigned int		 req_id;
+
+	/* Waiting for host to ack */
+	wait_queue_head_t	acked;
+	int			failed;
+};
+
+#define TYPE_TABLE_ENTRY(_entry)				\
+	{ PSTORE_TYPE_##_entry, VIRTIO_PSTORE_TYPE_##_entry }
+
+struct type_table {
+	int pstore;
+	u16 virtio;
+} type_table[] = {
+	TYPE_TABLE_ENTRY(DMESG),
+};
+
+#undef TYPE_TABLE_ENTRY
+
+
+static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(type_table); i++) {
+		if (type == type_table[i].pstore)
+			return cpu_to_virtio16(vps->vdev, type_table[i].virtio);
+	}
+
+	return cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
+}
+
+static enum pstore_type_id from_virtio_type(struct virtio_pstore *vps, u16
type)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(type_table); i++) {
+		if (virtio16_to_cpu(vps->vdev, type) == type_table[i].virtio)
+			return type_table[i].pstore;
+	}
+
+	return PSTORE_TYPE_UNKNOWN;
+}
+
+static void virtpstore_ack(struct virtqueue *vq)
+{
+	struct virtio_pstore *vps = vq->vdev->priv;
+
+	wake_up(&vps->acked);
+}
+
+static void virtpstore_check(struct virtqueue *vq)
+{
+	struct virtio_pstore *vps = vq->vdev->priv;
+	struct virtio_pstore_res *res;
+	unsigned int len;
+
+	res = virtqueue_get_buf(vq, &len);
+	if (res == NULL)
+		return;
+
+	if (virtio32_to_cpu(vq->vdev, res->ret) < 0)
+		vps->failed = 1;
+}
+
+static void virt_pstore_get_reqs(struct virtio_pstore *vps,
+				 struct virtio_pstore_req **preq,
+				 struct virtio_pstore_res **pres)
+{
+	unsigned int idx = vps->req_id++ % VIRT_PSTORE_NR_REQ;
+
+	*preq = &vps->req[idx];
+	*pres = &vps->res[idx];
+
+	memset(*preq, 0, sizeof(**preq));
+	memset(*pres, 0, sizeof(**pres));
+}
+
+static int virt_pstore_open(struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_req *req;
+	struct virtio_pstore_res *res;
+	struct scatterlist sgo[1], sgi[1];
+	struct scatterlist *sgs[2] = { sgo, sgi };
+	unsigned int len;
+
+	virt_pstore_get_reqs(vps, &req, &res);
+
+	req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_OPEN);
+
+	sg_init_one(sgo, req, sizeof(*req));
+	sg_init_one(sgi, res, sizeof(*res));
+	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq[0]);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
+	return virtio32_to_cpu(vps->vdev, res->ret);
+}
+
+static int virt_pstore_close(struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_req *req = &vps->req[vps->req_id];
+	struct virtio_pstore_res *res = &vps->res[vps->req_id];
+	struct scatterlist sgo[1], sgi[1];
+	struct scatterlist *sgs[2] = { sgo, sgi };
+	unsigned int len;
+
+	virt_pstore_get_reqs(vps, &req, &res);
+
+	req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_CLOSE);
+
+	sg_init_one(sgo, req, sizeof(*req));
+	sg_init_one(sgi, res, sizeof(*res));
+	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq[0]);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
+	return virtio32_to_cpu(vps->vdev, res->ret);
+}
+
+static ssize_t virt_pstore_read(u64 *id, enum pstore_type_id *type,
+				int *count, struct timespec *time,
+				char **buf, bool *compressed,
+				ssize_t *ecc_notice_size,
+				struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_req *req;
+	struct virtio_pstore_res *res;
+	struct virtio_pstore_fileinfo info;
+	struct scatterlist sgo[1], sgi[3];
+	struct scatterlist *sgs[2] = { sgo, sgi };
+	unsigned int len;
+	unsigned int flags;
+	int ret;
+	void *bf;
+
+	virt_pstore_get_reqs(vps, &req, &res);
+
+	req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_READ);
+
+	sg_init_one(sgo, req, sizeof(*req));
+	sg_init_table(sgi, 3);
+	sg_set_buf(&sgi[0], res, sizeof(*res));
+	sg_set_buf(&sgi[1], &info, sizeof(info));
+	sg_set_buf(&sgi[2], psi->buf, psi->bufsize);
+	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq[0]);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
+	if (len < sizeof(*res) + sizeof(info))
+		return -1;
+
+	ret = virtio32_to_cpu(vps->vdev, res->ret);
+	if (ret < 0)
+		return ret;
+
+	len = virtio32_to_cpu(vps->vdev, info.len);
+
+	bf = kmalloc(len, GFP_KERNEL);
+	if (bf == NULL)
+		return -ENOMEM;
+
+	*id    = virtio64_to_cpu(vps->vdev, info.id);
+	*type  = from_virtio_type(vps, info.type);
+	*count = virtio32_to_cpu(vps->vdev, info.count);
+
+	flags = virtio32_to_cpu(vps->vdev, info.flags);
+	*compressed = flags & VIRTIO_PSTORE_FL_COMPRESSED;
+
+	time->tv_sec  = virtio64_to_cpu(vps->vdev, info.time_sec);
+	time->tv_nsec = virtio32_to_cpu(vps->vdev, info.time_nsec);
+
+	memcpy(bf, psi->buf, len);
+	*buf = bf;
+
+	return len;
+}
+
+static int notrace virt_pstore_write(enum pstore_type_id type,
+				     enum kmsg_dump_reason reason,
+				     u64 *id, unsigned int part, int count,
+				     bool compressed, size_t size,
+				     struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_req *req;
+	struct virtio_pstore_res *res;
+	struct scatterlist sgo[2], sgi[1];
+	struct scatterlist *sgs[2] = { sgo, sgi };
+	unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
+
+	if (vps->failed)
+		return -1;
+
+	*id = vps->req_id;
+	virt_pstore_get_reqs(vps, &req, &res);
+
+	req->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
+	req->type  = to_virtio_type(vps, type);
+	req->flags = cpu_to_virtio32(vps->vdev, flags);
+
+	sg_init_table(sgo, 2);
+	sg_set_buf(&sgo[0], req, sizeof(*req));
+	sg_set_buf(&sgo[1], psi->buf, size);
+	sg_init_one(sgi, res, sizeof(*res));
+	virtqueue_add_sgs(vps->vq[1], sgs, 1, 1, vps, GFP_ATOMIC);
+	virtqueue_kick(vps->vq[1]);
+
+	return 0;
+}
+
+static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
+			     struct timespec time, struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_req *req;
+	struct virtio_pstore_res *res;
+	struct scatterlist sgo[1], sgi[1];
+	struct scatterlist *sgs[2] = { sgo, sgi };
+	unsigned int len;
+
+	virt_pstore_get_reqs(vps, &req, &res);
+
+	req->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
+	req->type  = to_virtio_type(vps, type);
+	req->id	   = cpu_to_virtio64(vps->vdev, id);
+	req->count = cpu_to_virtio32(vps->vdev, count);
+
+	sg_init_one(sgo, req, sizeof(*req));
+	sg_init_one(sgi, res, sizeof(*res));
+	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq[0]);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
+	return virtio32_to_cpu(vps->vdev, res->ret);
+}
+
+static int virt_pstore_init(struct virtio_pstore *vps)
+{
+	struct pstore_info *psinfo = &vps->pstore;
+	int err;
+
+	if (!psinfo->bufsize)
+		psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
+
+	psinfo->buf = alloc_pages_exact(psinfo->bufsize, GFP_KERNEL);
+	if (!psinfo->buf) {
+		pr_err("cannot allocate pstore buffer\n");
+		return -ENOMEM;
+	}
+
+	psinfo->owner = THIS_MODULE;
+	psinfo->name  = "virtio";
+	psinfo->open  = virt_pstore_open;
+	psinfo->close = virt_pstore_close;
+	psinfo->read  = virt_pstore_read;
+	psinfo->erase = virt_pstore_erase;
+	psinfo->write = virt_pstore_write;
+	psinfo->flags = PSTORE_FLAGS_FRAGILE;
+
+	psinfo->data  = vps;
+	spin_lock_init(&psinfo->buf_lock);
+
+	err = pstore_register(psinfo);
+	if (err)
+		kfree(psinfo->buf);
+
+	return err;
+}
+
+static int virt_pstore_exit(struct virtio_pstore *vps)
+{
+	struct pstore_info *psinfo = &vps->pstore;
+
+	pstore_unregister(psinfo);
+
+	free_pages_exact(psinfo->buf, psinfo->bufsize);
+	psinfo->buf = NULL;
+	psinfo->bufsize = 0;
+
+	return 0;
+}
+
+static int virtpstore_init_vqs(struct virtio_pstore *vps)
+{
+	vq_callback_t *callbacks[] = { virtpstore_ack, virtpstore_check };
+	const char *names[] = { "pstore_read", "pstore_write" };
+
+	return vps->vdev->config->find_vqs(vps->vdev, 2, vps->vq,
+					   callbacks, names);
+}
+
+static void virtpstore_init_config(struct virtio_pstore *vps)
+{
+	u32 bufsize;
+
+	virtio_cread(vps->vdev, struct virtio_pstore_config, bufsize,
&bufsize);
+
+	vps->pstore.bufsize = PAGE_ALIGN(bufsize);
+}
+
+static void virtpstore_confirm_config(struct virtio_pstore *vps)
+{
+	u32 bufsize = vps->pstore.bufsize;
+
+	virtio_cwrite(vps->vdev, struct virtio_pstore_config, bufsize,
+		     &bufsize);
+}
+
+static int virtpstore_probe(struct virtio_device *vdev)
+{
+	struct virtio_pstore *vps;
+	int err;
+
+	if (!vdev->config->get) {
+		dev_err(&vdev->dev, "driver init: config access
disabled\n");
+		return -EINVAL;
+	}
+
+	vdev->priv = vps = kzalloc(sizeof(*vps), GFP_KERNEL);
+	if (!vps) {
+		err = -ENOMEM;
+		goto out;
+	}
+	vps->vdev = vdev;
+
+	err = virtpstore_init_vqs(vps);
+	if (err < 0)
+		goto out_free;
+
+	virtpstore_init_config(vps);
+
+	err = virt_pstore_init(vps);
+	if (err)
+		goto out_del_vq;
+
+	virtpstore_confirm_config(vps);
+
+	init_waitqueue_head(&vps->acked);
+
+	virtio_device_ready(vdev);
+
+	dev_info(&vdev->dev, "driver init: ok (bufsize = %luK, flags =
%x)\n",
+		 vps->pstore.bufsize >> 10, vps->pstore.flags);
+
+	return 0;
+
+out_del_vq:
+	vdev->config->del_vqs(vdev);
+out_free:
+	kfree(vps);
+out:
+	dev_err(&vdev->dev, "driver init: failed with %d\n", err);
+	return err;
+}
+
+static void virtpstore_remove(struct virtio_device *vdev)
+{
+	struct virtio_pstore *vps = vdev->priv;
+
+	virt_pstore_exit(vps);
+
+	/* Now we reset the device so we can clean up the queues. */
+	vdev->config->reset(vdev);
+
+	vdev->config->del_vqs(vdev);
+
+	kfree(vps);
+}
+
+static unsigned int features[] = {
+};
+
+static struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_PSTORE, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+static struct virtio_driver virtio_pstore_driver = {
+	.driver.name         = KBUILD_MODNAME,
+	.driver.owner        = THIS_MODULE,
+	.feature_table       = features,
+	.feature_table_size  = ARRAY_SIZE(features),
+	.id_table            = id_table,
+	.probe               = virtpstore_probe,
+	.remove              = virtpstore_remove,
+};
+
+module_virtio_driver(virtio_pstore_driver);
+MODULE_DEVICE_TABLE(virtio, id_table);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Namhyung Kim <namhyung at kernel.org>");
+MODULE_DESCRIPTION("Virtio pstore driver");
diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
index 6d4e92ccdc91..9bbb1554d8b2 100644
--- a/include/uapi/linux/Kbuild
+++ b/include/uapi/linux/Kbuild
@@ -449,6 +449,7 @@ header-y += virtio_ids.h
 header-y += virtio_input.h
 header-y += virtio_net.h
 header-y += virtio_pci.h
+header-y += virtio_pstore.h
 header-y += virtio_ring.h
 header-y += virtio_rng.h
 header-y += virtio_scsi.h
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index 77925f587b15..c72a9ab588c0 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -41,5 +41,6 @@
 #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
 #define VIRTIO_ID_GPU          16 /* virtio GPU */
 #define VIRTIO_ID_INPUT        18 /* virtio input */
+#define VIRTIO_ID_PSTORE       22 /* virtio pstore */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
diff --git a/include/uapi/linux/virtio_pstore.h
b/include/uapi/linux/virtio_pstore.h
new file mode 100644
index 000000000000..f4b0d204d8ae
--- /dev/null
+++ b/include/uapi/linux/virtio_pstore.h
@@ -0,0 +1,74 @@
+#ifndef _LINUX_VIRTIO_PSTORE_H
+#define _LINUX_VIRTIO_PSTORE_H
+/* This header is BSD licensed so anyone can use the definitions to implement
+ * compatible drivers/servers.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of IBM nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE. */
+#include <linux/types.h>
+#include <linux/virtio_types.h>
+
+#define VIRTIO_PSTORE_CMD_NULL   0
+#define VIRTIO_PSTORE_CMD_OPEN   1
+#define VIRTIO_PSTORE_CMD_READ   2
+#define VIRTIO_PSTORE_CMD_WRITE  3
+#define VIRTIO_PSTORE_CMD_ERASE  4
+#define VIRTIO_PSTORE_CMD_CLOSE  5
+
+#define VIRTIO_PSTORE_TYPE_UNKNOWN  0
+#define VIRTIO_PSTORE_TYPE_DMESG    1
+
+#define VIRTIO_PSTORE_FL_COMPRESSED  1
+
+struct virtio_pstore_req {
+	__virtio16		cmd;
+	__virtio16		type;
+	__virtio32		flags;
+	__virtio64		id;
+	__virtio32		count;
+	__virtio32		reserved;
+};
+
+struct virtio_pstore_res {
+	__virtio16		cmd;
+	__virtio16		type;
+	__virtio32		ret;
+};
+
+struct virtio_pstore_fileinfo {
+	__virtio64		id;
+	__virtio32		count;
+	__virtio16		type;
+	__virtio16		unused;
+	__virtio32		flags;
+	__virtio32		len;
+	__virtio64		time_sec;
+	__virtio32		time_nsec;
+	__virtio32		reserved;
+};
+
+struct virtio_pstore_config {
+	__virtio32		bufsize;
+};
+
+#endif /* _LINUX_VIRTIO_PSTORE_H */
-- 
2.9.3

From: Namhyung Kim <namhyung at gmail.com>

Add virtio pstore device to allow kernel log files saved on the host.
It will save the log files on the directory given by pstore device
option.

  $ qemu-system-x86_64 -device virtio-pstore,directory=dir-xx ...

  (guest) # echo c > /proc/sysrq-trigger

  $ ls dir-xx
  dmesg-1.enc.z  dmesg-2.enc.z

The log files are usually compressed using zlib.  Users can see the log
messages directly on the host or on the guest (using pstore filesystem).

The 'directory' property is required for virtio-pstore device to work.
It also adds 'bufsize' property to set size of pstore bufer.

Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Radim Kr?m?? <rkrcmar at redhat.com>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: Anthony Liguori <aliguori at amazon.com>
Cc: Anton Vorontsov <anton at enomsg.org>
Cc: Colin Cross <ccross at android.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Tony Luck <tony.luck at intel.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Minchan Kim <minchan at kernel.org>
Cc: Daniel P. Berrange <berrange at redhat.com>
Cc: kvm at vger.kernel.org
Cc: qemu-devel at nongnu.org
Cc: virtualization at lists.linux-foundation.org
Signed-off-by: Namhyung Kim <namhyung at gmail.com>
---
 hw/virtio/Makefile.objs                        |   2 +-
 hw/virtio/virtio-pci.c                         |  52 ++
 hw/virtio/virtio-pci.h                         |  14 +
 hw/virtio/virtio-pstore.c                      | 689 +++++++++++++++++++++++++
 include/hw/pci/pci.h                           |   1 +
 include/hw/virtio/virtio-pstore.h              |  36 ++
 include/standard-headers/linux/virtio_ids.h    |   1 +
 include/standard-headers/linux/virtio_pstore.h |  76 +++
 qdev-monitor.c                                 |   1 +
 9 files changed, 871 insertions(+), 1 deletion(-)
 create mode 100644 hw/virtio/virtio-pstore.c
 create mode 100644 include/hw/virtio/virtio-pstore.h
 create mode 100644 include/standard-headers/linux/virtio_pstore.h

diff --git a/hw/virtio/Makefile.objs b/hw/virtio/Makefile.objs
index 3e2b175..aae7082 100644
--- a/hw/virtio/Makefile.objs
+++ b/hw/virtio/Makefile.objs
@@ -4,4 +4,4 @@ common-obj-y += virtio-bus.o
 common-obj-y += virtio-mmio.o
 
 obj-y += virtio.o virtio-balloon.o 
-obj-$(CONFIG_LINUX) += vhost.o vhost-backend.o vhost-user.o
+obj-$(CONFIG_LINUX) += vhost.o vhost-backend.o vhost-user.o virtio-pstore.o
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 755f921..c184823 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -2416,6 +2416,57 @@ static const TypeInfo virtio_host_pci_info = {
 };
 #endif
 
+/* virtio-pstore-pci */
+
+static void virtio_pstore_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
+{
+    VirtIOPstorePCI *vps = VIRTIO_PSTORE_PCI(vpci_dev);
+    DeviceState *vdev = DEVICE(&vps->vdev);
+    Error *err = NULL;
+
+    qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
+    object_property_set_bool(OBJECT(vdev), true, "realized",
&err);
+    if (err) {
+        error_propagate(errp, err);
+        return;
+    }
+}
+
+static void virtio_pstore_pci_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
+    PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
+
+    k->realize = virtio_pstore_pci_realize;
+    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
+
+    pcidev_k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
+    pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_PSTORE;
+    pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
+    pcidev_k->class_id = PCI_CLASS_OTHERS;
+}
+
+static void virtio_pstore_pci_instance_init(Object *obj)
+{
+    VirtIOPstorePCI *dev = VIRTIO_PSTORE_PCI(obj);
+
+    virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
+                                TYPE_VIRTIO_PSTORE);
+    object_property_add_alias(obj, "directory",
OBJECT(&dev->vdev),
+                              "directory", &error_abort);
+    object_property_add_alias(obj, "bufsize",
OBJECT(&dev->vdev),
+                              "bufsize", &error_abort);
+}
+
+static const TypeInfo virtio_pstore_pci_info = {
+    .name          = TYPE_VIRTIO_PSTORE_PCI,
+    .parent        = TYPE_VIRTIO_PCI,
+    .instance_size = sizeof(VirtIOPstorePCI),
+    .instance_init = virtio_pstore_pci_instance_init,
+    .class_init    = virtio_pstore_pci_class_init,
+};
+
 /* virtio-pci-bus */
 
 static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size,
@@ -2485,6 +2536,7 @@ static void virtio_pci_register_types(void)
 #ifdef CONFIG_VHOST_SCSI
     type_register_static(&vhost_scsi_pci_info);
 #endif
+    type_register_static(&virtio_pstore_pci_info);
 }
 
 type_init(virtio_pci_register_types)
diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
index 25fbf8a..354b2b7 100644
--- a/hw/virtio/virtio-pci.h
+++ b/hw/virtio/virtio-pci.h
@@ -31,6 +31,7 @@
 #ifdef CONFIG_VHOST_SCSI
 #include "hw/virtio/vhost-scsi.h"
 #endif
+#include "hw/virtio/virtio-pstore.h"
 
 typedef struct VirtIOPCIProxy VirtIOPCIProxy;
 typedef struct VirtIOBlkPCI VirtIOBlkPCI;
@@ -44,6 +45,7 @@ typedef struct VirtIOInputPCI VirtIOInputPCI;
 typedef struct VirtIOInputHIDPCI VirtIOInputHIDPCI;
 typedef struct VirtIOInputHostPCI VirtIOInputHostPCI;
 typedef struct VirtIOGPUPCI VirtIOGPUPCI;
+typedef struct VirtIOPstorePCI VirtIOPstorePCI;
 
 /* virtio-pci-bus */
 
@@ -324,6 +326,18 @@ struct VirtIOGPUPCI {
     VirtIOGPU vdev;
 };
 
+/*
+ * virtio-pstore-pci: This extends VirtioPCIProxy.
+ */
+#define TYPE_VIRTIO_PSTORE_PCI "virtio-pstore-pci"
+#define VIRTIO_PSTORE_PCI(obj) \
+        OBJECT_CHECK(VirtIOPstorePCI, (obj), TYPE_VIRTIO_PSTORE_PCI)
+
+struct VirtIOPstorePCI {
+    VirtIOPCIProxy parent_obj;
+    VirtIOPstore vdev;
+};
+
 /* Virtio ABI version, if we increment this, we break the guest driver. */
 #define VIRTIO_PCI_ABI_VERSION          0
 
diff --git a/hw/virtio/virtio-pstore.c b/hw/virtio/virtio-pstore.c
new file mode 100644
index 0000000..08d1063
--- /dev/null
+++ b/hw/virtio/virtio-pstore.c
@@ -0,0 +1,689 @@
+/*
+ * Virtio Pstore Device
+ *
+ * Copyright (C) 2016  LG Electronics
+ *
+ * Authors:
+ *  Namhyung Kim  <namhyung at gmail.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include <stdio.h>
+
+#include "qemu/osdep.h"
+#include "qemu/iov.h"
+#include "qemu-common.h"
+#include "qemu/cutils.h"
+#include "qemu/error-report.h"
+#include "sysemu/kvm.h"
+#include "qapi/visitor.h"
+#include "qapi-event.h"
+#include "io/channel-file.h"
+#include "trace.h"
+
+#include "hw/virtio/virtio.h"
+#include "hw/virtio/virtio-bus.h"
+#include "hw/virtio/virtio-access.h"
+#include "hw/virtio/virtio-pstore.h"
+
+#define PSTORE_DEFAULT_BUFSIZE   (16 * 1024)
+#define PSTORE_DEFAULT_FILE_MAX  5
+
+/* the index should match to the type value */
+static const char *virtio_pstore_file_prefix[] = {
+    "unknown-",		/* VIRTIO_PSTORE_TYPE_UNKNOWN */
+    "dmesg-",		/* VIRTIO_PSTORE_TYPE_DMESG */
+};
+
+static char *virtio_pstore_to_filename(VirtIOPstore *s,
+                                       struct virtio_pstore_req *req)
+{
+    const char *basename;
+    unsigned long long id;
+    unsigned int type = le16_to_cpu(req->type);
+    unsigned int flags = le32_to_cpu(req->flags);
+
+    if (type < ARRAY_SIZE(virtio_pstore_file_prefix)) {
+        basename = virtio_pstore_file_prefix[type];
+    } else {
+        basename = "unknown-";
+    }
+
+    id = s->id++;
+    return g_strdup_printf("%s/%s%llu%s", s->directory, basename,
id,
+                            flags & VIRTIO_PSTORE_FL_COMPRESSED ?
".enc.z" : "");
+}
+
+static char *virtio_pstore_from_filename(VirtIOPstore *s, char *name,
+                                         struct virtio_pstore_fileinfo *info)
+{
+    char *filename;
+    unsigned int idx;
+
+    filename = g_strdup_printf("%s/%s", s->directory, name);
+    if (filename == NULL)
+        return NULL;
+
+    for (idx = 0; idx < ARRAY_SIZE(virtio_pstore_file_prefix); idx++) {
+        if (g_str_has_prefix(name, virtio_pstore_file_prefix[idx])) {
+            info->type = idx;
+            name += strlen(virtio_pstore_file_prefix[idx]);
+            break;
+        }
+    }
+
+    if (idx == ARRAY_SIZE(virtio_pstore_file_prefix)) {
+        g_free(filename);
+        return NULL;
+    }
+
+    qemu_strtoull(name, NULL, 0, &info->id);
+
+    info->flags = 0;
+    if (g_str_has_suffix(name, ".enc.z")) {
+        info->flags |= VIRTIO_PSTORE_FL_COMPRESSED;
+    }
+
+    return filename;
+}
+
+static int prefix_idx;
+static int prefix_count;
+static int prefix_len;
+
+static int filter_pstore(const struct dirent *de)
+{
+    int i;
+
+    for (i = 0; i < prefix_count; i++) {
+        const char *prefix = virtio_pstore_file_prefix[prefix_idx + i];
+
+        if (g_str_has_prefix(de->d_name, prefix)) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+static int sort_pstore(const struct dirent **a, const struct dirent **b)
+{
+    uint64_t id_a, id_b;
+
+    qemu_strtoull((*a)->d_name + prefix_len, NULL, 0, &id_a);
+    qemu_strtoull((*b)->d_name + prefix_len, NULL, 0, &id_b);
+
+    return id_a - id_b;
+}
+
+static int delete_old_pstore_file(VirtIOPstore *s, unsigned short type)
+{
+    int ret = 0;
+    int i, num;
+    char *filename;
+    struct dirent **files;
+
+    if (type >= ARRAY_SIZE(virtio_pstore_file_prefix)) {
+        type = VIRTIO_PSTORE_TYPE_UNKNOWN;
+    }
+
+    prefix_idx = type;
+    prefix_len = strlen(virtio_pstore_file_prefix[type]);
+    prefix_count = 1;  /* only scan current type */
+
+    /* delete the oldest file in the same type */
+    num = scandir(s->directory, &files, filter_pstore, sort_pstore);
+    if (num < 0)
+        return num;
+    if (num < (int)s->file_max)
+        goto out;
+
+    filename = g_strdup_printf("%s/%s", s->directory,
files[0]->d_name);
+    if (filename == NULL) {
+        ret = -1;
+        goto out;
+    }
+
+    ret = unlink(filename);
+
+out:
+    for (i = 0; i < num; i++) {
+        g_free(files[i]);
+    }
+    g_free(files);
+
+    return ret;
+}
+
+static ssize_t virtio_pstore_do_open(VirtIOPstore *s)
+{
+    /* scan all pstore files */
+    prefix_idx = 0;
+    prefix_count = ARRAY_SIZE(virtio_pstore_file_prefix);
+
+    s->file_idx = 0;
+    s->num_file = scandir(s->directory, &s->files, filter_pstore,
alphasort);
+
+    return s->num_file >= 0 ? 0 : -1;
+}
+
+static ssize_t virtio_pstore_do_close(VirtIOPstore *s)
+{
+    int i;
+
+    for (i = 0; i < s->num_file; i++) {
+        g_free(s->files[i]);
+    }
+    g_free(s->files);
+    s->files = NULL;
+
+    s->num_file = 0;
+    return 0;
+}
+
+static ssize_t virtio_pstore_do_erase(VirtIOPstore *s,
+                                      struct virtio_pstore_req *req)
+{
+    char *filename;
+    int ret;
+
+    filename = virtio_pstore_to_filename(s, req);
+    if (filename == NULL)
+        return -1;
+
+    ret = unlink(filename);
+
+    g_free(filename);
+    return ret;
+}
+
+struct pstore_read_arg {
+    VirtIOPstore *vps;
+    VirtQueueElement *elem;
+    struct virtio_pstore_fileinfo info;
+    QIOChannel *ioc;
+};
+
+static gboolean pstore_async_read_fn(QIOChannel *ioc, GIOCondition condition,
+                                     gpointer data)
+{
+    struct pstore_read_arg *rarg = data;
+    struct virtio_pstore_fileinfo *info = &rarg->info;
+    VirtIOPstore *vps = rarg->vps;
+    VirtQueueElement *elem = rarg->elem;
+    struct virtio_pstore_res res;
+    size_t offset = sizeof(res) + sizeof(*info);
+    struct iovec *sg = elem->in_sg;
+    unsigned int sg_num = elem->in_num;
+    Error *err = NULL;
+    ssize_t len;
+    int ret;
+
+    /* skip res and fileinfo */
+    iov_discard_front(&sg, &sg_num, sizeof(res) + sizeof(*info));
+
+    len = qio_channel_readv(rarg->ioc, sg, sg_num, &err);
+    if (len < 0) {
+        if (errno == EAGAIN) {
+            len = 0;
+        }
+        ret = -1;
+    } else {
+        info->len = cpu_to_le32(len);
+        ret = 0;
+    }
+
+    res.cmd  = cpu_to_le16(VIRTIO_PSTORE_CMD_READ);
+    res.type = cpu_to_le16(VIRTIO_PSTORE_TYPE_UNKNOWN);
+    res.ret  = cpu_to_le32(ret);
+
+    /* now copy res and fileinfo */
+    iov_from_buf(elem->in_sg, elem->in_num, 0, &res, sizeof(res));
+    iov_from_buf(elem->in_sg, elem->in_num, sizeof(res), info,
sizeof(*info));
+
+    len += offset;
+    virtqueue_push(vps->rvq, elem, len);
+    virtio_notify(VIRTIO_DEVICE(vps), vps->rvq);
+
+    return FALSE;
+}
+
+static void free_rarg_fn(gpointer data)
+{
+    struct pstore_read_arg *rarg = data;
+
+    qio_channel_close(rarg->ioc, NULL);
+
+    g_free(rarg->elem);
+    g_free(rarg);
+}
+
+static ssize_t virtio_pstore_do_read(VirtIOPstore *s, VirtQueueElement *elem)
+{
+    char *filename = NULL;
+    int idx;
+    struct stat stbuf;
+    struct pstore_read_arg *rarg = NULL;
+    QIOChannelFile *iocf;
+    Error *err = NULL;
+    int ret = -1;
+
+    if (s->file_idx >= s->num_file) {
+        return 0;
+    }
+
+    rarg = g_malloc(sizeof(*rarg));
+    if (rarg == NULL) {
+        return -1;
+    }
+
+    idx = s->file_idx++;
+    filename = virtio_pstore_from_filename(s, s->files[idx]->d_name,
+                                           &rarg->info);
+    if (filename == NULL) {
+        goto out;
+    }
+
+    iocf = qio_channel_file_new_path(filename, O_RDONLY, 0644, &err);
+    if (err) {
+        error_reportf_err(err, "cannot create io channel: ");
+        goto out;
+    }
+
+    if (fstat(iocf->fd, &stbuf) < 0) {
+        goto out;
+    }
+
+    rarg->vps            = s;
+    rarg->elem           = elem;
+    rarg->ioc            = QIO_CHANNEL(iocf);
+    rarg->info.id        = cpu_to_le64(rarg->info.id);
+    rarg->info.type      = cpu_to_le16(rarg->info.type);
+    rarg->info.flags     = cpu_to_le32(rarg->info.flags);
+    rarg->info.time_sec  = cpu_to_le64(stbuf.st_ctim.tv_sec);
+    rarg->info.time_nsec = cpu_to_le32(stbuf.st_ctim.tv_nsec);
+
+    qio_channel_set_blocking(rarg->ioc, false, &err);
+    qio_channel_add_watch(rarg->ioc, G_IO_IN, pstore_async_read_fn, rarg,
+                          free_rarg_fn);
+    g_free(filename);
+    return 1;
+
+out:
+    g_free(filename);
+    g_free(rarg);
+
+    return ret;
+}
+
+struct pstore_write_arg {
+    VirtIOPstore *vps;
+    VirtQueueElement *elem;
+    struct virtio_pstore_req *req;
+    QIOChannel *ioc;
+};
+
+static gboolean pstore_async_write_fn(QIOChannel *ioc, GIOCondition condition,
+                                      gpointer data)
+{
+    struct pstore_write_arg *warg = data;
+    VirtIOPstore *vps = warg->vps;
+    VirtQueueElement *elem = warg->elem;
+    struct iovec *sg = elem->out_sg;
+    unsigned int sg_num = elem->out_num;
+    struct virtio_pstore_res res;
+    Error *err = NULL;
+    ssize_t len;
+    int ret;
+
+    /* we already consumed the req */
+    iov_discard_front(&sg, &sg_num, sizeof(*warg->req));
+
+    len = qio_channel_writev(warg->ioc, sg, sg_num, &err);
+    if (len < 0) {
+        ret = -1;
+    } else {
+        ret = 0;
+    }
+
+    res.cmd  = cpu_to_le16(VIRTIO_PSTORE_CMD_WRITE);
+    res.type = warg->req->type;
+    res.ret  = cpu_to_le32(ret);
+
+    /* tell the result to guest */
+    iov_from_buf(elem->in_sg, elem->in_num, 0, &res, sizeof(res));
+
+    virtqueue_push(vps->wvq, elem, sizeof(res));
+    virtio_notify(VIRTIO_DEVICE(vps), vps->wvq);
+
+    return FALSE;
+}
+
+static void free_warg_fn(gpointer data)
+{
+    struct pstore_write_arg *warg = data;
+
+    qio_channel_close(warg->ioc, NULL);
+
+    g_free(warg->elem);
+    g_free(warg);
+}
+
+static ssize_t virtio_pstore_do_write(VirtIOPstore *s, VirtQueueElement *elem,
+                                      struct virtio_pstore_req *req)
+{
+    unsigned short type = le16_to_cpu(req->type);
+    char *filename = NULL;
+    int flags = O_WRONLY | O_CREAT | O_TRUNC;
+    struct pstore_write_arg *warg = NULL;
+    QIOChannelFile *iocf;
+    Error *err = NULL;
+    int ret = -1;
+
+    /* do not keep same type of files more than 'file-max' */
+    delete_old_pstore_file(s, type);
+
+    filename = virtio_pstore_to_filename(s, req);
+    if (filename == NULL) {
+        return -1;
+    }
+
+    iocf = qio_channel_file_new_path(filename, flags, 0644, &err);
+    if (err) {
+        error_reportf_err(err, "cannot create io channel: ");
+        goto out;
+    }
+
+    warg = g_malloc(sizeof(*warg));
+    if (warg == NULL) {
+        goto out;
+    }
+
+    warg->vps  = s;
+    warg->elem = elem;
+    warg->req  = req;
+    warg->ioc  = QIO_CHANNEL(iocf);
+
+    qio_channel_set_blocking(warg->ioc, false, &err);
+    qio_channel_add_watch(warg->ioc, G_IO_OUT, pstore_async_write_fn, warg,
+                          free_warg_fn);
+    g_free(filename);
+    return 1;
+
+out:
+    g_free(filename);
+    g_free(warg);
+    return ret;
+}
+
+static void virtio_pstore_handle_io(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOPstore *s = VIRTIO_PSTORE(vdev);
+    VirtQueueElement *elem;
+    struct virtio_pstore_req req;
+    struct virtio_pstore_res res;
+    ssize_t len = 0;
+    int ret;
+
+    for (;;) {
+        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+        if (!elem) {
+            return;
+        }
+
+        if (elem->out_num < 1 || elem->in_num < 1) {
+            error_report("request or response buffer is missing");
+            exit(1);
+        }
+
+        if (elem->out_num > 2 || elem->in_num > 3) {
+            error_report("invalid number of input/output buffer");
+            exit(1);
+        }
+
+        len = iov_to_buf(elem->out_sg, elem->out_num, 0, &req,
sizeof(req));
+        if (len != (ssize_t)sizeof(req)) {
+            error_report("invalid request size: %ld", (long)len);
+            exit(1);
+        }
+        res.cmd  = req.cmd;
+        res.type = req.type;
+
+        switch (le16_to_cpu(req.cmd)) {
+        case VIRTIO_PSTORE_CMD_OPEN:
+            ret = virtio_pstore_do_open(s);
+            break;
+        case VIRTIO_PSTORE_CMD_CLOSE:
+            ret = virtio_pstore_do_close(s);
+            break;
+        case VIRTIO_PSTORE_CMD_ERASE:
+            ret = virtio_pstore_do_erase(s, &req);
+            break;
+        case VIRTIO_PSTORE_CMD_READ:
+            ret = virtio_pstore_do_read(s, elem);
+            if (ret == 1) {
+                /* async channel io */
+                continue;
+            }
+            break;
+        case VIRTIO_PSTORE_CMD_WRITE:
+            ret = virtio_pstore_do_write(s, elem, &req);
+            if (ret == 1) {
+                /* async channel io */
+                continue;
+            }
+            break;
+        default:
+            ret = -1;
+            break;
+        }
+
+        res.ret = ret;
+
+        iov_from_buf(elem->in_sg, elem->in_num, 0, &res,
sizeof(res));
+        virtqueue_push(vq, elem, sizeof(res) + len);
+
+        virtio_notify(vdev, vq);
+        g_free(elem);
+
+        if (ret < 0) {
+            return;
+        }
+    }
+}
+
+static void virtio_pstore_device_realize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VirtIOPstore *s = VIRTIO_PSTORE(dev);
+
+    virtio_init(vdev, "virtio-pstore", VIRTIO_ID_PSTORE,
+                sizeof(struct virtio_pstore_config));
+
+    s->id = 1;
+
+    if (!s->bufsize)
+        s->bufsize = PSTORE_DEFAULT_BUFSIZE;
+    if (!s->file_max)
+        s->file_max = PSTORE_DEFAULT_FILE_MAX;
+
+    s->rvq = virtio_add_queue(vdev, 128, virtio_pstore_handle_io);
+    s->wvq = virtio_add_queue(vdev, 128, virtio_pstore_handle_io);
+}
+
+static void virtio_pstore_device_unrealize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+
+    virtio_cleanup(vdev);
+}
+
+static void virtio_pstore_get_config(VirtIODevice *vdev, uint8_t *config_data)
+{
+    VirtIOPstore *dev = VIRTIO_PSTORE(vdev);
+    struct virtio_pstore_config config;
+
+    config.bufsize = cpu_to_le32(dev->bufsize);
+
+    memcpy(config_data, &config, sizeof(struct virtio_pstore_config));
+}
+
+static void virtio_pstore_set_config(VirtIODevice *vdev,
+                                     const uint8_t *config_data)
+{
+    VirtIOPstore *dev = VIRTIO_PSTORE(vdev);
+    struct virtio_pstore_config config;
+
+    memcpy(&config, config_data, sizeof(struct virtio_pstore_config));
+
+    dev->bufsize = le32_to_cpu(config.bufsize);
+}
+
+static uint64_t get_features(VirtIODevice *vdev, uint64_t f, Error **errp)
+{
+    return f;
+}
+
+static void pstore_get_directory(Object *obj, Visitor *v,
+                                 const char *name, void *opaque,
+                                 Error **errp)
+{
+    VirtIOPstore *s = opaque;
+
+    visit_type_str(v, name, &s->directory, errp);
+}
+
+static void pstore_set_directory(Object *obj, Visitor *v,
+                                 const char *name, void *opaque,
+                                 Error **errp)
+{
+    VirtIOPstore *s = opaque;
+    Error *local_err = NULL;
+    char *value;
+
+    visit_type_str(v, name, &value, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    g_free(s->directory);
+    s->directory = value;
+}
+
+static void pstore_release_directory(Object *obj, const char *name,
+                                     void *opaque)
+{
+    VirtIOPstore *s = opaque;
+
+    g_free(s->directory);
+    s->directory = NULL;
+}
+
+static void pstore_get_bufsize(Object *obj, Visitor *v,
+                               const char *name, void *opaque,
+                               Error **errp)
+{
+    VirtIOPstore *s = opaque;
+    uint64_t value = s->bufsize;
+
+    visit_type_size(v, name, &value, errp);
+}
+
+static void pstore_set_bufsize(Object *obj, Visitor *v,
+                               const char *name, void *opaque,
+                               Error **errp)
+{
+    VirtIOPstore *s = opaque;
+    Error *error = NULL;
+    uint64_t value;
+
+    visit_type_size(v, name, &value, &error);
+    if (error) {
+        error_propagate(errp, error);
+        return;
+    }
+
+    if (value < 4096) {
+        error_setg(&error, "Warning: too small buffer size:
%"PRIu64, value);
+        error_propagate(errp, error);
+        return;
+    }
+
+    s->bufsize = value;
+}
+
+static void pstore_get_file_max(Object *obj, Visitor *v,
+                                const char *name, void *opaque,
+                                Error **errp)
+{
+    VirtIOPstore *s = opaque;
+    int64_t value = s->file_max;
+
+    visit_type_int(v, name, &value, errp);
+}
+
+static void pstore_set_file_max(Object *obj, Visitor *v,
+                                const char *name, void *opaque,
+                                Error **errp)
+{
+    VirtIOPstore *s = opaque;
+    Error *error = NULL;
+    int64_t value;
+
+    visit_type_int(v, name, &value, &error);
+    if (error) {
+        error_propagate(errp, error);
+        return;
+    }
+
+    s->file_max = value;
+}
+
+static Property virtio_pstore_properties[] = {
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void virtio_pstore_instance_init(Object *obj)
+{
+    VirtIOPstore *s = VIRTIO_PSTORE(obj);
+
+    object_property_add(obj, "directory", "str",
+                        pstore_get_directory, pstore_set_directory,
+                        pstore_release_directory, s, NULL);
+    object_property_add(obj, "bufsize", "size",
+                        pstore_get_bufsize, pstore_set_bufsize, NULL, s, NULL);
+    object_property_add(obj, "file-max", "int",
+                        pstore_get_file_max, pstore_set_file_max, NULL, s,
NULL);
+}
+
+static void virtio_pstore_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
+
+    dc->props = virtio_pstore_properties;
+    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
+    vdc->realize = virtio_pstore_device_realize;
+    vdc->unrealize = virtio_pstore_device_unrealize;
+    vdc->get_config = virtio_pstore_get_config;
+    vdc->set_config = virtio_pstore_set_config;
+    vdc->get_features = get_features;
+}
+
+static const TypeInfo virtio_pstore_info = {
+    .name = TYPE_VIRTIO_PSTORE,
+    .parent = TYPE_VIRTIO_DEVICE,
+    .instance_size = sizeof(VirtIOPstore),
+    .instance_init = virtio_pstore_instance_init,
+    .class_init = virtio_pstore_class_init,
+};
+
+static void virtio_register_types(void)
+{
+    type_register_static(&virtio_pstore_info);
+}
+
+type_init(virtio_register_types)
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index 929ec2f..b31774a 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -79,6 +79,7 @@
 #define PCI_DEVICE_ID_VIRTIO_SCSI        0x1004
 #define PCI_DEVICE_ID_VIRTIO_RNG         0x1005
 #define PCI_DEVICE_ID_VIRTIO_9P          0x1009
+#define PCI_DEVICE_ID_VIRTIO_PSTORE      0x100a
 
 #define PCI_VENDOR_ID_REDHAT             0x1b36
 #define PCI_DEVICE_ID_REDHAT_BRIDGE      0x0001
diff --git a/include/hw/virtio/virtio-pstore.h
b/include/hw/virtio/virtio-pstore.h
new file mode 100644
index 0000000..85b1828
--- /dev/null
+++ b/include/hw/virtio/virtio-pstore.h
@@ -0,0 +1,36 @@
+/*
+ * Virtio Pstore Support
+ *
+ * Authors:
+ *  Namhyung Kim      <namhyung at gmail.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef _QEMU_VIRTIO_PSTORE_H
+#define _QEMU_VIRTIO_PSTORE_H
+
+#include "standard-headers/linux/virtio_pstore.h"
+#include "hw/virtio/virtio.h"
+#include "hw/pci/pci.h"
+
+#define TYPE_VIRTIO_PSTORE "virtio-pstore-device"
+#define VIRTIO_PSTORE(obj) \
+        OBJECT_CHECK(VirtIOPstore, (obj), TYPE_VIRTIO_PSTORE)
+
+typedef struct VirtIOPstore {
+    VirtIODevice    parent_obj;
+    VirtQueue      *rvq;
+    VirtQueue      *wvq;
+    char           *directory;
+    int             file_idx;
+    int             num_file;
+    struct dirent **files;
+    uint64_t        id;
+    uint64_t        bufsize;
+    uint64_t        file_max;
+} VirtIOPstore;
+
+#endif
diff --git a/include/standard-headers/linux/virtio_ids.h
b/include/standard-headers/linux/virtio_ids.h
index 77925f5..c72a9ab 100644
--- a/include/standard-headers/linux/virtio_ids.h
+++ b/include/standard-headers/linux/virtio_ids.h
@@ -41,5 +41,6 @@
 #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
 #define VIRTIO_ID_GPU          16 /* virtio GPU */
 #define VIRTIO_ID_INPUT        18 /* virtio input */
+#define VIRTIO_ID_PSTORE       22 /* virtio pstore */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
diff --git a/include/standard-headers/linux/virtio_pstore.h
b/include/standard-headers/linux/virtio_pstore.h
new file mode 100644
index 0000000..2f91839
--- /dev/null
+++ b/include/standard-headers/linux/virtio_pstore.h
@@ -0,0 +1,76 @@
+#ifndef _LINUX_VIRTIO_PSTORE_H
+#define _LINUX_VIRTIO_PSTORE_H
+/* This header is BSD licensed so anyone can use the definitions to implement
+ * compatible drivers/servers.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of IBM nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE. */
+#include "standard-headers/linux/types.h"
+#include "standard-headers/linux/virtio_types.h"
+#include "standard-headers/linux/virtio_ids.h"
+#include "standard-headers/linux/virtio_config.h"
+
+#define VIRTIO_PSTORE_CMD_NULL   0
+#define VIRTIO_PSTORE_CMD_OPEN   1
+#define VIRTIO_PSTORE_CMD_READ   2
+#define VIRTIO_PSTORE_CMD_WRITE  3
+#define VIRTIO_PSTORE_CMD_ERASE  4
+#define VIRTIO_PSTORE_CMD_CLOSE  5
+
+#define VIRTIO_PSTORE_TYPE_UNKNOWN  0
+#define VIRTIO_PSTORE_TYPE_DMESG    1
+
+#define VIRTIO_PSTORE_FL_COMPRESSED  1
+
+struct virtio_pstore_req {
+    __virtio16 cmd;
+    __virtio16 type;
+    __virtio32 flags;
+    __virtio64 id;
+    __virtio32 count;
+    __virtio32 reserved;
+};
+
+struct virtio_pstore_res {
+    __virtio16 cmd;
+    __virtio16 type;
+    __virtio32 ret;
+};
+
+struct virtio_pstore_fileinfo {
+    __virtio64 id;
+    __virtio32 count;
+    __virtio16 type;
+    __virtio16 unused;
+    __virtio32 flags;
+    __virtio32 len;
+    __virtio64 time_sec;
+    __virtio32 time_nsec;
+    __virtio32 reserved;
+};
+
+struct virtio_pstore_config {
+    __virtio32 bufsize;
+};
+
+#endif /* _LINUX_VIRTIO_PSTORE_H */
diff --git a/qdev-monitor.c b/qdev-monitor.c
index e19617f..e1df5a9 100644
--- a/qdev-monitor.c
+++ b/qdev-monitor.c
@@ -73,6 +73,7 @@ static const QDevAlias qdev_alias_table[] = {
     { "virtio-serial-pci", "virtio-serial", QEMU_ARCH_ALL
& ~QEMU_ARCH_S390X },
     { "virtio-tablet-ccw", "virtio-tablet", QEMU_ARCH_S390X
},
     { "virtio-tablet-pci", "virtio-tablet", QEMU_ARCH_ALL
& ~QEMU_ARCH_S390X },
+    { "virtio-pstore-pci", "virtio-pstore" },
     { }
 };
 
-- 
2.9.3

From: Namhyung Kim <namhyung at gmail.com>

Add virtio pstore device to allow kernel log messages saved on the
host.  With this patch, it will save the log files under directory given
by --pstore option.

  $ lkvm run --pstore=dir-xx

  (guest) # echo c > /proc/sysrq-trigger

  $ ls dir-xx
  dmesg-1.enc.z  dmesg-2.enc.z

The log files are usually compressed using zlib.  User can easily see
the messages on the host or on the guest (using pstore filesystem).

Cc: Will Deacon <will.deacon at arm.com>
Signed-off-by: Namhyung Kim <namhyung at gmail.com>
---
 Makefile                     |   1 +
 builtin-run.c                |   2 +
 include/kvm/kvm-config.h     |   1 +
 include/kvm/virtio-pci-dev.h |   2 +
 include/kvm/virtio-pstore.h  |  53 +++++
 include/linux/virtio_ids.h   |   1 +
 virtio/pstore.c              | 447 +++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 507 insertions(+)
 create mode 100644 include/kvm/virtio-pstore.h
 create mode 100644 virtio/pstore.c

diff --git a/Makefile b/Makefile
index 1f0196f..d7462b9 100644
--- a/Makefile
+++ b/Makefile
@@ -67,6 +67,7 @@ OBJS	+= virtio/net.o
 OBJS	+= virtio/rng.o
 OBJS    += virtio/balloon.o
 OBJS	+= virtio/pci.o
+OBJS	+= virtio/pstore.o
 OBJS	+= disk/blk.o
 OBJS	+= disk/qcow.o
 OBJS	+= disk/raw.o
diff --git a/builtin-run.c b/builtin-run.c
index 72b878d..08c12dd 100644
--- a/builtin-run.c
+++ b/builtin-run.c
@@ -128,6 +128,8 @@ void kvm_run_set_wrapper_sandbox(void)
 			" rootfs"),					\
 	OPT_STRING('\0', "hugetlbfs", &(cfg)->hugetlbfs_path,
"path",	\
 			"Hugetlbfs path"),				\
+	OPT_STRING('\0', "pstore", &(cfg)->pstore_path,
"path",		\
+			"pstore data path"),				\
 									\
 	OPT_GROUP("Kernel options:"),					\
 	OPT_STRING('k', "kernel", &(cfg)->kernel_filename,
"kernel",	\
diff --git a/include/kvm/kvm-config.h b/include/kvm/kvm-config.h
index 386fa8c..42b7651 100644
--- a/include/kvm/kvm-config.h
+++ b/include/kvm/kvm-config.h
@@ -45,6 +45,7 @@ struct kvm_config {
 	const char *hugetlbfs_path;
 	const char *custom_rootfs_name;
 	const char *real_cmdline;
+	const char *pstore_path;
 	struct virtio_net_params *net_params;
 	bool single_step;
 	bool vnc;
diff --git a/include/kvm/virtio-pci-dev.h b/include/kvm/virtio-pci-dev.h
index 48ae018..4339d94 100644
--- a/include/kvm/virtio-pci-dev.h
+++ b/include/kvm/virtio-pci-dev.h
@@ -15,6 +15,7 @@
 #define PCI_DEVICE_ID_VIRTIO_BLN		0x1005
 #define PCI_DEVICE_ID_VIRTIO_SCSI		0x1008
 #define PCI_DEVICE_ID_VIRTIO_9P			0x1009
+#define PCI_DEVICE_ID_VIRTIO_PSTORE		0x100a
 #define PCI_DEVICE_ID_VESA			0x2000
 #define PCI_DEVICE_ID_PCI_SHMEM			0x0001
 
@@ -34,5 +35,6 @@
 #define PCI_CLASS_RNG				0xff0000
 #define PCI_CLASS_BLN				0xff0000
 #define PCI_CLASS_9P				0xff0000
+#define PCI_CLASS_PSTORE			0xff0000
 
 #endif /* VIRTIO_PCI_DEV_H_ */
diff --git a/include/kvm/virtio-pstore.h b/include/kvm/virtio-pstore.h
new file mode 100644
index 0000000..9f52ffd
--- /dev/null
+++ b/include/kvm/virtio-pstore.h
@@ -0,0 +1,53 @@
+#ifndef KVM__PSTORE_VIRTIO_H
+#define KVM__PSTORE_VIRTIO_H
+
+#include <kvm/virtio.h>
+#include <sys/types.h>
+
+#define VIRTIO_PSTORE_CMD_NULL   0
+#define VIRTIO_PSTORE_CMD_OPEN   1
+#define VIRTIO_PSTORE_CMD_READ   2
+#define VIRTIO_PSTORE_CMD_WRITE  3
+#define VIRTIO_PSTORE_CMD_ERASE  4
+#define VIRTIO_PSTORE_CMD_CLOSE  5
+
+#define VIRTIO_PSTORE_TYPE_UNKNOWN  0
+#define VIRTIO_PSTORE_TYPE_DMESG    1
+
+#define VIRTIO_PSTORE_FL_COMPRESSED  1
+
+struct virtio_pstore_req {
+	__virtio16		cmd;
+	__virtio16		type;
+	__virtio32		flags;
+	__virtio64		id;
+	__virtio32		count;
+	__virtio32		reserved;
+};
+
+struct virtio_pstore_res {
+	__virtio16		cmd;
+	__virtio16		type;
+	__virtio32		ret;
+};
+
+struct virtio_pstore_fileinfo {
+	__virtio64		id;
+	__virtio32		count;
+	__virtio16		type;
+	__virtio16		unused;
+	__virtio32		flags;
+	__virtio32		len;
+	__virtio64		time_sec;
+	__virtio32		time_nsec;
+	__virtio32		reserved;
+};
+
+struct virtio_pstore_config {
+	__virtio32		bufsize;
+};
+
+int virtio_pstore__init(struct kvm *kvm);
+int virtio_pstore__exit(struct kvm *kvm);
+
+#endif /* KVM__PSTORE_VIRTIO_H */
diff --git a/include/linux/virtio_ids.h b/include/linux/virtio_ids.h
index 5f60aa4..40eabf7 100644
--- a/include/linux/virtio_ids.h
+++ b/include/linux/virtio_ids.h
@@ -40,5 +40,6 @@
 #define VIRTIO_ID_RPROC_SERIAL 11 /* virtio remoteproc serial link */
 #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
 #define VIRTIO_ID_INPUT        18 /* virtio input */
+#define VIRTIO_ID_PSTORE       22 /* virtio pstore */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
diff --git a/virtio/pstore.c b/virtio/pstore.c
new file mode 100644
index 0000000..fb9806f
--- /dev/null
+++ b/virtio/pstore.c
@@ -0,0 +1,447 @@
+#include "kvm/virtio-pstore.h"
+
+#include "kvm/virtio-pci-dev.h"
+
+#include "kvm/virtio.h"
+#include "kvm/util.h"
+#include "kvm/kvm.h"
+#include "kvm/threadpool.h"
+#include "kvm/guest_compat.h"
+
+#include <linux/virtio_ring.h>
+
+#include <linux/list.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <pthread.h>
+#include <linux/kernel.h>
+#include <sys/eventfd.h>
+
+#define NUM_VIRT_QUEUES			2
+#define VIRTIO_PSTORE_QUEUE_SIZE	128
+
+struct io_thread_arg {
+	struct kvm		*kvm;
+	struct pstore_dev	*pdev;
+};
+
+struct pstore_dev {
+	struct list_head	list;
+	struct virtio_device	vdev;
+	pthread_t		io_thread;
+	int			io_efd;
+	int			done;
+
+	struct virtio_pstore_config *config;
+
+	int			fd;
+	DIR			*dir;
+	u64			id;
+
+	/* virtio queue */
+	struct virt_queue	vqs[NUM_VIRT_QUEUES];
+};
+
+static LIST_HEAD(pdevs);
+static int compat_id = -1;
+
+static u8 *get_config(struct kvm *kvm, void *dev)
+{
+	struct pstore_dev *pdev = dev;
+
+	return (u8*)pdev->config;
+}
+
+static u32 get_host_features(struct kvm *kvm, void *dev)
+{
+	/* Unused */
+	return 0;
+}
+
+static void set_guest_features(struct kvm *kvm, void *dev, u32 features)
+{
+	/* Unused */
+}
+
+static void virtio_pstore_to_filename(struct kvm *kvm, struct pstore_dev *pdev,
+				      char *buf, size_t sz,
+				      struct virtio_pstore_req *req)
+{
+	const char *basename;
+	unsigned long long id = 0;
+	unsigned int flags = virtio_host_to_guest_u64(pdev->vqs, req->flags);
+
+	switch (req->type) {
+	case VIRTIO_PSTORE_TYPE_DMESG:
+		basename = "dmesg";
+		id = pdev->id++;
+		break;
+	default:
+		basename = "unknown";
+		break;
+	}
+
+	snprintf(buf, sz, "%s/%s-%llu%s", kvm->cfg.pstore_path, basename,
id,
+		 flags & VIRTIO_PSTORE_FL_COMPRESSED ? ".enc.z" :
"");
+}
+
+static void virtio_pstore_from_filename(struct kvm *kvm, char *name,
+					char *buf, size_t sz,
+					struct virtio_pstore_fileinfo *info)
+{
+	size_t len = strlen(name);
+
+	snprintf(buf, sz, "%s/%s", kvm->cfg.pstore_path, name);
+
+	info->flags = 0;
+	if (len > 6 && !strncmp(name + len - 6, ".enc.z", 6))
+		info->flags |= VIRTIO_PSTORE_FL_COMPRESSED;
+
+	if (!strncmp(name, "dmesg-", 6)) {
+		info->type = VIRTIO_PSTORE_TYPE_DMESG;
+		name += strlen("dmesg-");
+	} else if (!strncmp(name, "unknown-", 8)) {
+		info->type = VIRTIO_PSTORE_TYPE_UNKNOWN;
+		name += strlen("unknown-");
+	}
+
+	info->id = strtoul(name, NULL, 0);
+}
+
+static int virtio_pstore_do_open(struct kvm *kvm, struct pstore_dev *pdev,
+				 struct virtio_pstore_req *req,
+				 struct iovec *iov)
+{
+	pdev->dir = opendir(kvm->cfg.pstore_path);
+	if (pdev->dir == NULL)
+		return -errno;
+
+	return 0;
+}
+
+static int virtio_pstore_do_close(struct kvm *kvm, struct pstore_dev *pdev,
+				  struct virtio_pstore_req *req,
+				  struct iovec *iov)
+{
+	if (pdev->dir == NULL)
+		return -1;
+
+	closedir(pdev->dir);
+	pdev->dir = NULL;
+
+	return 0;
+}
+
+static ssize_t virtio_pstore_do_read(struct kvm *kvm, struct pstore_dev *pdev,
+				     struct virtio_pstore_req *req,
+				     struct iovec *iov,
+				     struct virtio_pstore_fileinfo *info)
+{
+	char path[PATH_MAX];
+	FILE *fp;
+	ssize_t len = 0;
+	struct stat stbuf;
+	struct dirent *dent;
+
+	if (pdev->dir == NULL)
+		return 0;
+
+	dent = readdir(pdev->dir);
+	while (dent) {
+		if (dent->d_name[0] != '.')
+			break;
+		dent = readdir(pdev->dir);
+	}
+
+	if (dent == NULL)
+		return 0;
+
+	virtio_pstore_from_filename(kvm, dent->d_name, path, sizeof(path), info);
+	fp = fopen(path, "r");
+	if (fp == NULL)
+		return -1;
+
+	if (fstat(fileno(fp), &stbuf) < 0)
+		return -1;
+
+	len = fread(iov[3].iov_base, 1, iov[3].iov_len, fp);
+	if (len < 0 && errno == EAGAIN) {
+		len = 0;
+		goto out;
+	}
+
+	info->id     = virtio_host_to_guest_u64(pdev->vqs, info->id);
+	info->type   = virtio_host_to_guest_u64(pdev->vqs, info->type);
+	info->flags  = virtio_host_to_guest_u32(pdev->vqs, info->flags);
+	info->len    = virtio_host_to_guest_u32(pdev->vqs, len);
+
+	info->time_sec  = virtio_host_to_guest_u64(pdev->vqs,
stbuf.st_ctim.tv_sec);
+	info->time_nsec = virtio_host_to_guest_u32(pdev->vqs,
stbuf.st_ctim.tv_nsec);
+
+	len += sizeof(*info);
+
+out:
+	fclose(fp);
+	return len;
+}
+
+static ssize_t virtio_pstore_do_write(struct kvm *kvm, struct pstore_dev *pdev,
+				      struct virtio_pstore_req *req,
+				      struct iovec *iov)
+{
+	char path[PATH_MAX];
+	FILE *fp;
+	ssize_t len = 0;
+
+	virtio_pstore_to_filename(kvm, pdev, path, sizeof(path), req);
+
+	fp = fopen(path, "a");
+	if (fp == NULL)
+		return -1;
+
+	len = fwrite(iov[1].iov_base, 1, iov[1].iov_len, fp);
+	if (len < 0 && errno == EAGAIN)
+		len = 0;
+
+	fclose(fp);
+	return 0;
+}
+
+static ssize_t virtio_pstore_do_erase(struct kvm *kvm, struct pstore_dev *pdev,
+				      struct virtio_pstore_req *req,
+				      struct iovec *iov)
+{
+	char path[PATH_MAX];
+
+	virtio_pstore_to_filename(kvm, pdev, path, sizeof(path), req);
+
+	return unlink(path);
+}
+
+static bool virtio_pstore_do_io_request(struct kvm *kvm, struct pstore_dev
*pdev,
+					struct virt_queue *vq)
+{
+	struct iovec iov[VIRTIO_PSTORE_QUEUE_SIZE];
+	struct virtio_pstore_req *req;
+	struct virtio_pstore_res *res;
+	struct virtio_pstore_fileinfo *info;
+	ssize_t len = 0;
+	u16 out, in, head;
+	int ret = 0;
+
+	head = virt_queue__get_iov(vq, iov, &out, &in, kvm);
+
+	if (iov[0].iov_len != sizeof(*req) || iov[out].iov_len != sizeof(*res)) {
+		return false;
+	}
+
+	req = iov[0].iov_base;
+	res = iov[out].iov_base;
+
+	switch (virtio_guest_to_host_u16(vq, req->cmd)) {
+	case VIRTIO_PSTORE_CMD_OPEN:
+		ret = virtio_pstore_do_open(kvm, pdev, req, iov);
+		break;
+	case VIRTIO_PSTORE_CMD_READ:
+		info = iov[out + 1].iov_base;
+		ret = virtio_pstore_do_read(kvm, pdev, req, iov, info);
+		if (ret > 0) {
+			len = ret;
+			ret = 0;
+		}
+		break;
+	case VIRTIO_PSTORE_CMD_WRITE:
+		ret = virtio_pstore_do_write(kvm, pdev, req, iov);
+		break;
+	case VIRTIO_PSTORE_CMD_CLOSE:
+		ret = virtio_pstore_do_close(kvm, pdev, req, iov);
+		break;
+	case VIRTIO_PSTORE_CMD_ERASE:
+		ret = virtio_pstore_do_erase(kvm, pdev, req, iov);
+		break;
+	default:
+		return false;
+	}
+
+	res->cmd  = req->cmd;
+	res->type = req->type;
+	res->ret  = virtio_host_to_guest_u32(vq, ret);
+
+	virt_queue__set_used_elem(vq, head, sizeof(*res) + len);
+
+	return ret == 0;
+}
+
+static void virtio_pstore_do_io(struct kvm *kvm, struct pstore_dev *pdev,
+				struct virt_queue *vq)
+{
+	bool done = false;
+
+	while (virt_queue__available(vq)) {
+		virtio_pstore_do_io_request(kvm, pdev, vq);
+		done = true;
+	}
+
+	if (done)
+		pdev->vdev.ops->signal_vq(kvm, &pdev->vdev, vq - pdev->vqs);
+}
+
+static void *virtio_pstore_io_thread(void *arg)
+{
+	struct io_thread_arg *io_arg = arg;
+	struct pstore_dev *pdev = io_arg->pdev;
+	struct kvm *kvm = io_arg->kvm;
+	u64 data;
+	int r;
+
+	kvm__set_thread_name("virtio-pstore-io");
+
+	while (!pdev->done) {
+		r = read(pdev->io_efd, &data, sizeof(u64));
+		if (r < 0)
+			continue;
+
+		virtio_pstore_do_io(kvm, pdev, &pdev->vqs[0]);
+		virtio_pstore_do_io(kvm, pdev, &pdev->vqs[1]);
+	}
+	free(io_arg);
+
+	pthread_exit(NULL);
+	return NULL;
+}
+
+static int init_vq(struct kvm *kvm, void *dev, u32 vq, u32 page_size, u32
align,
+		   u32 pfn)
+{
+	struct pstore_dev *pdev = dev;
+	struct virt_queue *queue;
+	void *p;
+
+	compat__remove_message(compat_id);
+
+	queue		= &pdev->vqs[vq];
+	queue->pfn	= pfn;
+	p		= virtio_get_vq(kvm, queue->pfn, page_size);
+
+	vring_init(&queue->vring, VIRTIO_PSTORE_QUEUE_SIZE, p, align);
+
+	return 0;
+}
+
+static int notify_vq(struct kvm *kvm, void *dev, u32 vq)
+{
+	struct pstore_dev *pdev = dev;
+	u64 data = 1;
+	int r;
+
+	r = write(pdev->io_efd, &data, sizeof(data));
+	if (r < 0)
+		return r;
+
+	return 0;
+}
+
+static int get_pfn_vq(struct kvm *kvm, void *dev, u32 vq)
+{
+	struct pstore_dev *pdev = dev;
+
+	return pdev->vqs[vq].pfn;
+}
+
+static int get_size_vq(struct kvm *kvm, void *dev, u32 vq)
+{
+	return VIRTIO_PSTORE_QUEUE_SIZE;
+}
+
+static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
+{
+	/* FIXME: dynamic */
+	return size;
+}
+
+static struct virtio_ops pstore_dev_virtio_ops = {
+	.get_config		= get_config,
+	.get_host_features	= get_host_features,
+	.set_guest_features	= set_guest_features,
+	.init_vq		= init_vq,
+	.notify_vq		= notify_vq,
+	.get_pfn_vq		= get_pfn_vq,
+	.get_size_vq		= get_size_vq,
+	.set_size_vq		= set_size_vq,
+};
+
+int virtio_pstore__init(struct kvm *kvm)
+{
+	struct pstore_dev *pdev;
+	struct io_thread_arg *io_arg = NULL;
+	int r;
+
+	if (!kvm->cfg.pstore_path)
+		return 0;
+
+	pdev = calloc(1, sizeof(*pdev));
+	if (pdev == NULL)
+		return -ENOMEM;
+
+	pdev->config = calloc(1, sizeof(*pdev->config));
+	if (pdev->config == NULL) {
+		r = -ENOMEM;
+		goto cleanup;
+	}
+
+	pdev->id = 1;
+
+	io_arg = malloc(sizeof(*io_arg));
+	if (io_arg == NULL) {
+		r = -ENOMEM;
+		goto cleanup;
+	}
+
+	pdev->io_efd = eventfd(0, 0);
+
+	*io_arg = (struct io_thread_arg) {
+		.pdev   = pdev,
+		.kvm    = kvm,
+	};
+	r = pthread_create(&pdev->io_thread, NULL,
+			   virtio_pstore_io_thread, io_arg);
+	if (r < 0)
+		goto cleanup;
+
+	r = virtio_init(kvm, pdev, &pdev->vdev, &pstore_dev_virtio_ops,
+			VIRTIO_DEFAULT_TRANS(kvm), PCI_DEVICE_ID_VIRTIO_PSTORE,
+			VIRTIO_ID_PSTORE, PCI_CLASS_PSTORE);
+	if (r < 0)
+		goto cleanup;
+
+	list_add_tail(&pdev->list, &pdevs);
+
+	if (compat_id == -1)
+		compat_id = virtio_compat_add_message("virtio-pstore",
"CONFIG_VIRTIO_PSTORE");
+	return 0;
+
+cleanup:
+	free(io_arg);
+	free(pdev->config);
+	free(pdev);
+
+	return r;
+}
+virtio_dev_init(virtio_pstore__init);
+
+int virtio_pstore__exit(struct kvm *kvm)
+{
+	struct pstore_dev *pdev, *tmp;
+
+	list_for_each_entry_safe(pdev, tmp, &pdevs, list) {
+		list_del(&pdev->list);
+		close(pdev->io_efd);
+		pdev->vdev.ops->exit(kvm, &pdev->vdev);
+		free(pdev);
+	}
+
+	return 0;
+}
+virtio_dev_exit(virtio_pstore__exit);
-- 
2.9.3

On Wed, Aug 31, 2016 at 05:08:00PM +0900, Namhyung Kim
wrote:
> The virtio pstore driver provides interface to the pstore subsystem so
> that the guest kernel's log/dump message can be saved on the host
> machine.  Users can access the log file directly on the host, or on the
> guest at the next boot using pstore filesystem.  It currently deals with
> kernel log (printk) buffer only, but we can extend it to have other
> information (like ftrace dump) later.
> 
> It supports legacy PCI device using single order-2 page buffer.  It uses
> two virtqueues - one for (sync) read and another for (async) write.
> Since it cannot wait for write finished, it supports up to 128
> concurrent IO.  The buffer size is configurable now.
> 
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Radim Kr?m?? <rkrcmar at redhat.com>
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Cc: Anthony Liguori <aliguori at amazon.com>
> Cc: Anton Vorontsov <anton at enomsg.org>
> Cc: Colin Cross <ccross at android.com>
> Cc: Kees Cook <keescook at chromium.org>
> Cc: Tony Luck <tony.luck at intel.com>
> Cc: Steven Rostedt <rostedt at goodmis.org>
> Cc: Ingo Molnar <mingo at kernel.org>
> Cc: Minchan Kim <minchan at kernel.org>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: kvm at vger.kernel.org
> Cc: qemu-devel at nongnu.org
> Cc: virtualization at lists.linux-foundation.org
> Cc: virtio-dev at lists.oasis-open.org
> Signed-off-by: Namhyung Kim <namhyung at kernel.org>
> ---
>  drivers/virtio/Kconfig             |  10 +
>  drivers/virtio/Makefile            |   1 +
>  drivers/virtio/virtio_pstore.c     | 417
+++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/Kbuild          |   1 +
>  include/uapi/linux/virtio_ids.h    |   1 +
>  include/uapi/linux/virtio_pstore.h |  74 +++++++
>  6 files changed, 504 insertions(+)
>  create mode 100644 drivers/virtio/virtio_pstore.c
>  create mode 100644 include/uapi/linux/virtio_pstore.h
> 
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 77590320d44c..8f0e6c796c12 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -58,6 +58,16 @@ config VIRTIO_INPUT
>  
>  	 If unsure, say M.
>  
> +config VIRTIO_PSTORE
> +	tristate "Virtio pstore driver"
> +	depends on VIRTIO
> +	depends on PSTORE
> +	---help---
> +	 This driver supports virtio pstore devices to save/restore
> +	 panic and oops messages on the host.
> +
> +	 If unsure, say M.
> +
>   config VIRTIO_MMIO
>  	tristate "Platform bus driver for memory mapped virtio devices"
>  	depends on HAS_IOMEM && HAS_DMA
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 41e30e3dc842..bee68cb26d48 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -5,3 +5,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
>  virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
>  obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
>  obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
> +obj-$(CONFIG_VIRTIO_PSTORE) += virtio_pstore.o
> diff --git a/drivers/virtio/virtio_pstore.c
b/drivers/virtio/virtio_pstore.c
> new file mode 100644
> index 000000000000..ec41f0d2f0b7
> --- /dev/null
> +++ b/drivers/virtio/virtio_pstore.c
> @@ -0,0 +1,417 @@
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/pstore.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <uapi/linux/virtio_ids.h>
> +#include <uapi/linux/virtio_pstore.h>
> +
> +#define VIRT_PSTORE_ORDER    2
> +#define VIRT_PSTORE_BUFSIZE  (4096 << VIRT_PSTORE_ORDER)
> +#define VIRT_PSTORE_NR_REQ   128
> +
> +struct virtio_pstore {
> +	struct virtio_device	*vdev;
> +	struct virtqueue	*vq[2];
> +	struct pstore_info	 pstore;
> +	struct virtio_pstore_req req[VIRT_PSTORE_NR_REQ];
> +	struct virtio_pstore_res res[VIRT_PSTORE_NR_REQ];
> +	unsigned int		 req_id;
> +
> +	/* Waiting for host to ack */
> +	wait_queue_head_t	acked;
> +	int			failed;
> +};
> +
> +#define TYPE_TABLE_ENTRY(_entry)				\
> +	{ PSTORE_TYPE_##_entry, VIRTIO_PSTORE_TYPE_##_entry }
> +
> +struct type_table {
> +	int pstore;
> +	u16 virtio;
> +} type_table[] = {
> +	TYPE_TABLE_ENTRY(DMESG),
> +};
> +
> +#undef TYPE_TABLE_ENTRY
> +
> +
> +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id
type)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(type_table); i++) {
> +		if (type == type_table[i].pstore)
> +			return cpu_to_virtio16(vps->vdev, type_table[i].virtio);
Does this pass sparse checks? If yes I'm surprised - this clearly
returns a virtio16 type.

> +	}
> +
> +	return cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
> +}
> +
> +static enum pstore_type_id from_virtio_type(struct virtio_pstore *vps, u16
type)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(type_table); i++) {
> +		if (virtio16_to_cpu(vps->vdev, type) == type_table[i].virtio)
> +			return type_table[i].pstore;
> +	}
> +
> +	return PSTORE_TYPE_UNKNOWN;
> +}
> +
> +static void virtpstore_ack(struct virtqueue *vq)
> +{
> +	struct virtio_pstore *vps = vq->vdev->priv;
> +
> +	wake_up(&vps->acked);
> +}
> +
> +static void virtpstore_check(struct virtqueue *vq)
> +{
> +	struct virtio_pstore *vps = vq->vdev->priv;
> +	struct virtio_pstore_res *res;
> +	unsigned int len;
> +
> +	res = virtqueue_get_buf(vq, &len);
> +	if (res == NULL)
> +		return;
> +
> +	if (virtio32_to_cpu(vq->vdev, res->ret) < 0)
> +		vps->failed = 1;
> +}
> +
> +static void virt_pstore_get_reqs(struct virtio_pstore *vps,
> +				 struct virtio_pstore_req **preq,
> +				 struct virtio_pstore_res **pres)
> +{
> +	unsigned int idx = vps->req_id++ % VIRT_PSTORE_NR_REQ;
> +
> +	*preq = &vps->req[idx];
> +	*pres = &vps->res[idx];
> +
> +	memset(*preq, 0, sizeof(**preq));
> +	memset(*pres, 0, sizeof(**pres));
> +}
> +
> +static int virt_pstore_open(struct pstore_info *psi)
> +{
> +	struct virtio_pstore *vps = psi->data;
> +	struct virtio_pstore_req *req;
> +	struct virtio_pstore_res *res;
> +	struct scatterlist sgo[1], sgi[1];
> +	struct scatterlist *sgs[2] = { sgo, sgi };
> +	unsigned int len;
> +
> +	virt_pstore_get_reqs(vps, &req, &res);
> +
> +	req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_OPEN);
> +
> +	sg_init_one(sgo, req, sizeof(*req));
> +	sg_init_one(sgi, res, sizeof(*res));
> +	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +	virtqueue_kick(vps->vq[0]);
> +
> +	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +	return virtio32_to_cpu(vps->vdev, res->ret);
> +}
> +
> +static int virt_pstore_close(struct pstore_info *psi)
> +{
> +	struct virtio_pstore *vps = psi->data;
> +	struct virtio_pstore_req *req = &vps->req[vps->req_id];
> +	struct virtio_pstore_res *res = &vps->res[vps->req_id];
> +	struct scatterlist sgo[1], sgi[1];
> +	struct scatterlist *sgs[2] = { sgo, sgi };
> +	unsigned int len;
> +
> +	virt_pstore_get_reqs(vps, &req, &res);
> +
> +	req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_CLOSE);
> +
> +	sg_init_one(sgo, req, sizeof(*req));
> +	sg_init_one(sgi, res, sizeof(*res));
> +	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +	virtqueue_kick(vps->vq[0]);
> +
> +	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +	return virtio32_to_cpu(vps->vdev, res->ret);
> +}
> +
> +static ssize_t virt_pstore_read(u64 *id, enum pstore_type_id *type,
> +				int *count, struct timespec *time,
> +				char **buf, bool *compressed,
> +				ssize_t *ecc_notice_size,
> +				struct pstore_info *psi)
> +{
> +	struct virtio_pstore *vps = psi->data;
> +	struct virtio_pstore_req *req;
> +	struct virtio_pstore_res *res;
> +	struct virtio_pstore_fileinfo info;
> +	struct scatterlist sgo[1], sgi[3];
> +	struct scatterlist *sgs[2] = { sgo, sgi };
> +	unsigned int len;
> +	unsigned int flags;
> +	int ret;
> +	void *bf;
> +
> +	virt_pstore_get_reqs(vps, &req, &res);
> +
> +	req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_READ);
> +
> +	sg_init_one(sgo, req, sizeof(*req));
> +	sg_init_table(sgi, 3);
> +	sg_set_buf(&sgi[0], res, sizeof(*res));
> +	sg_set_buf(&sgi[1], &info, sizeof(info));
> +	sg_set_buf(&sgi[2], psi->buf, psi->bufsize);
> +	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +	virtqueue_kick(vps->vq[0]);
> +
> +	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +	if (len < sizeof(*res) + sizeof(info))
> +		return -1;
> +
> +	ret = virtio32_to_cpu(vps->vdev, res->ret);
> +	if (ret < 0)
> +		return ret;
> +
> +	len = virtio32_to_cpu(vps->vdev, info.len);
> +
> +	bf = kmalloc(len, GFP_KERNEL);
> +	if (bf == NULL)
> +		return -ENOMEM;
> +
> +	*id    = virtio64_to_cpu(vps->vdev, info.id);
> +	*type  = from_virtio_type(vps, info.type);
> +	*count = virtio32_to_cpu(vps->vdev, info.count);
> +
> +	flags = virtio32_to_cpu(vps->vdev, info.flags);
> +	*compressed = flags & VIRTIO_PSTORE_FL_COMPRESSED;
> +
> +	time->tv_sec  = virtio64_to_cpu(vps->vdev, info.time_sec);
> +	time->tv_nsec = virtio32_to_cpu(vps->vdev, info.time_nsec);
> +
> +	memcpy(bf, psi->buf, len);
> +	*buf = bf;
> +
> +	return len;
> +}
> +
> +static int notrace virt_pstore_write(enum pstore_type_id type,
> +				     enum kmsg_dump_reason reason,
> +				     u64 *id, unsigned int part, int count,
> +				     bool compressed, size_t size,
> +				     struct pstore_info *psi)
> +{
> +	struct virtio_pstore *vps = psi->data;
> +	struct virtio_pstore_req *req;
> +	struct virtio_pstore_res *res;
> +	struct scatterlist sgo[2], sgi[1];
> +	struct scatterlist *sgs[2] = { sgo, sgi };
> +	unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
> +
> +	if (vps->failed)
> +		return -1;
> +
> +	*id = vps->req_id;
> +	virt_pstore_get_reqs(vps, &req, &res);
> +
> +	req->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
> +	req->type  = to_virtio_type(vps, type);
> +	req->flags = cpu_to_virtio32(vps->vdev, flags);
> +
> +	sg_init_table(sgo, 2);
> +	sg_set_buf(&sgo[0], req, sizeof(*req));
> +	sg_set_buf(&sgo[1], psi->buf, size);
> +	sg_init_one(sgi, res, sizeof(*res));
> +	virtqueue_add_sgs(vps->vq[1], sgs, 1, 1, vps, GFP_ATOMIC);
> +	virtqueue_kick(vps->vq[1]);
> +
> +	return 0;
> +}
> +
> +static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
> +			     struct timespec time, struct pstore_info *psi)
> +{
> +	struct virtio_pstore *vps = psi->data;
> +	struct virtio_pstore_req *req;
> +	struct virtio_pstore_res *res;
> +	struct scatterlist sgo[1], sgi[1];
> +	struct scatterlist *sgs[2] = { sgo, sgi };
> +	unsigned int len;
> +
> +	virt_pstore_get_reqs(vps, &req, &res);
> +
> +	req->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
> +	req->type  = to_virtio_type(vps, type);
> +	req->id	   = cpu_to_virtio64(vps->vdev, id);
> +	req->count = cpu_to_virtio32(vps->vdev, count);
> +
> +	sg_init_one(sgo, req, sizeof(*req));
> +	sg_init_one(sgi, res, sizeof(*res));
> +	virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +	virtqueue_kick(vps->vq[0]);
> +
> +	wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +	return virtio32_to_cpu(vps->vdev, res->ret);
> +}
> +
> +static int virt_pstore_init(struct virtio_pstore *vps)
> +{
> +	struct pstore_info *psinfo = &vps->pstore;
> +	int err;
> +
> +	if (!psinfo->bufsize)
> +		psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
> +
> +	psinfo->buf = alloc_pages_exact(psinfo->bufsize, GFP_KERNEL);
> +	if (!psinfo->buf) {
> +		pr_err("cannot allocate pstore buffer\n");
> +		return -ENOMEM;
> +	}
> +
> +	psinfo->owner = THIS_MODULE;
> +	psinfo->name  = "virtio";
> +	psinfo->open  = virt_pstore_open;
> +	psinfo->close = virt_pstore_close;
> +	psinfo->read  = virt_pstore_read;
> +	psinfo->erase = virt_pstore_erase;
> +	psinfo->write = virt_pstore_write;
> +	psinfo->flags = PSTORE_FLAGS_FRAGILE;
> +
> +	psinfo->data  = vps;
> +	spin_lock_init(&psinfo->buf_lock);
> +
> +	err = pstore_register(psinfo);
> +	if (err)
> +		kfree(psinfo->buf);
> +
> +	return err;
> +}
> +
> +static int virt_pstore_exit(struct virtio_pstore *vps)
> +{
> +	struct pstore_info *psinfo = &vps->pstore;
> +
> +	pstore_unregister(psinfo);
> +
> +	free_pages_exact(psinfo->buf, psinfo->bufsize);
> +	psinfo->buf = NULL;
> +	psinfo->bufsize = 0;
> +
> +	return 0;
> +}
> +
> +static int virtpstore_init_vqs(struct virtio_pstore *vps)
> +{
> +	vq_callback_t *callbacks[] = { virtpstore_ack, virtpstore_check };
> +	const char *names[] = { "pstore_read", "pstore_write"
};
> +
> +	return vps->vdev->config->find_vqs(vps->vdev, 2, vps->vq,
> +					   callbacks, names);
> +}
> +
> +static void virtpstore_init_config(struct virtio_pstore *vps)
> +{
> +	u32 bufsize;
> +
> +	virtio_cread(vps->vdev, struct virtio_pstore_config, bufsize,
&bufsize);
> +
> +	vps->pstore.bufsize = PAGE_ALIGN(bufsize);
> +}
> +
> +static void virtpstore_confirm_config(struct virtio_pstore *vps)
> +{
> +	u32 bufsize = vps->pstore.bufsize;
> +
> +	virtio_cwrite(vps->vdev, struct virtio_pstore_config, bufsize,
> +		     &bufsize);
> +}
> +
> +static int virtpstore_probe(struct virtio_device *vdev)
> +{
> +	struct virtio_pstore *vps;
> +	int err;
> +
> +	if (!vdev->config->get) {
> +		dev_err(&vdev->dev, "driver init: config access
disabled\n");
> +		return -EINVAL;
> +	}
> +
> +	vdev->priv = vps = kzalloc(sizeof(*vps), GFP_KERNEL);
> +	if (!vps) {
> +		err = -ENOMEM;
> +		goto out;
> +	}
> +	vps->vdev = vdev;
> +
> +	err = virtpstore_init_vqs(vps);
> +	if (err < 0)
> +		goto out_free;
> +
> +	virtpstore_init_config(vps);
> +
> +	err = virt_pstore_init(vps);
> +	if (err)
> +		goto out_del_vq;
> +
> +	virtpstore_confirm_config(vps);
> +
> +	init_waitqueue_head(&vps->acked);
> +
> +	virtio_device_ready(vdev);
> +
> +	dev_info(&vdev->dev, "driver init: ok (bufsize = %luK, flags
= %x)\n",
> +		 vps->pstore.bufsize >> 10, vps->pstore.flags);
> +
> +	return 0;
> +
> +out_del_vq:
> +	vdev->config->del_vqs(vdev);
> +out_free:
> +	kfree(vps);
> +out:
> +	dev_err(&vdev->dev, "driver init: failed with %d\n",
err);
> +	return err;
> +}
> +
> +static void virtpstore_remove(struct virtio_device *vdev)
> +{
> +	struct virtio_pstore *vps = vdev->priv;
> +
> +	virt_pstore_exit(vps);
> +
> +	/* Now we reset the device so we can clean up the queues. */
> +	vdev->config->reset(vdev);
> +
> +	vdev->config->del_vqs(vdev);
> +
> +	kfree(vps);
> +}
> +
> +static unsigned int features[] = {
> +};
> +
> +static struct virtio_device_id id_table[] = {
> +	{ VIRTIO_ID_PSTORE, VIRTIO_DEV_ANY_ID },
> +	{ 0 },
> +};
> +
> +static struct virtio_driver virtio_pstore_driver = {
> +	.driver.name         = KBUILD_MODNAME,
> +	.driver.owner        = THIS_MODULE,
> +	.feature_table       = features,
> +	.feature_table_size  = ARRAY_SIZE(features),
> +	.id_table            = id_table,
> +	.probe               = virtpstore_probe,
> +	.remove              = virtpstore_remove,
> +};
> +
> +module_virtio_driver(virtio_pstore_driver);
> +MODULE_DEVICE_TABLE(virtio, id_table);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Namhyung Kim <namhyung at kernel.org>");
> +MODULE_DESCRIPTION("Virtio pstore driver");
> diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
> index 6d4e92ccdc91..9bbb1554d8b2 100644
> --- a/include/uapi/linux/Kbuild
> +++ b/include/uapi/linux/Kbuild
> @@ -449,6 +449,7 @@ header-y += virtio_ids.h
>  header-y += virtio_input.h
>  header-y += virtio_net.h
>  header-y += virtio_pci.h
> +header-y += virtio_pstore.h
>  header-y += virtio_ring.h
>  header-y += virtio_rng.h
>  header-y += virtio_scsi.h
> diff --git a/include/uapi/linux/virtio_ids.h
b/include/uapi/linux/virtio_ids.h
> index 77925f587b15..c72a9ab588c0 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -41,5 +41,6 @@
>  #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
>  #define VIRTIO_ID_GPU          16 /* virtio GPU */
>  #define VIRTIO_ID_INPUT        18 /* virtio input */
> +#define VIRTIO_ID_PSTORE       22 /* virtio pstore */
>  
>  #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/include/uapi/linux/virtio_pstore.h
b/include/uapi/linux/virtio_pstore.h
> new file mode 100644
> index 000000000000..f4b0d204d8ae
> --- /dev/null
> +++ b/include/uapi/linux/virtio_pstore.h
> @@ -0,0 +1,74 @@
> +#ifndef _LINUX_VIRTIO_PSTORE_H
> +#define _LINUX_VIRTIO_PSTORE_H
> +/* This header is BSD licensed so anyone can use the definitions to
implement
> + * compatible drivers/servers.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + * 3. Neither the name of IBM nor the names of its contributors
> + *    may be used to endorse or promote products derived from this
software
> + *    without specific prior written permission.
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
``AS IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
> + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE
> + * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
> + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL
> + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
> + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
> + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT
> + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
WAY
> + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE. */
> +#include <linux/types.h>
> +#include <linux/virtio_types.h>
> +
> +#define VIRTIO_PSTORE_CMD_NULL   0
> +#define VIRTIO_PSTORE_CMD_OPEN   1
> +#define VIRTIO_PSTORE_CMD_READ   2
> +#define VIRTIO_PSTORE_CMD_WRITE  3
> +#define VIRTIO_PSTORE_CMD_ERASE  4
> +#define VIRTIO_PSTORE_CMD_CLOSE  5
> +
> +#define VIRTIO_PSTORE_TYPE_UNKNOWN  0
> +#define VIRTIO_PSTORE_TYPE_DMESG    1
> +
> +#define VIRTIO_PSTORE_FL_COMPRESSED  1
> +
> +struct virtio_pstore_req {
> +	__virtio16		cmd;
> +	__virtio16		type;
> +	__virtio32		flags;
> +	__virtio64		id;
> +	__virtio32		count;
> +	__virtio32		reserved;
> +};
> +
> +struct virtio_pstore_res {
> +	__virtio16		cmd;
> +	__virtio16		type;
> +	__virtio32		ret;
> +};
Is there a reason to support legacy endian-ness?
If not, you can just use __le formats.

> +struct virtio_pstore_fileinfo {
> +	__virtio64		id;
> +	__virtio32		count;
> +	__virtio16		type;
> +	__virtio16		unused;
> +	__virtio32		flags;
> +	__virtio32		len;
> +	__virtio64		time_sec;
> +	__virtio32		time_nsec;
> +	__virtio32		reserved;
> +};
> +
> +struct virtio_pstore_config {
> +	__virtio32		bufsize;
> +};
> +
> +#endif /* _LINUX_VIRTIO_PSTORE_H */
> -- 
> 2.9.3