Xen devel - Jul 2013 - [PATCH 0 of 4 v2] blktap3/libxl: add support for blktap3 in libxl

This patch series implements support for blktap3 in libxl.

Supporting blktap3 requires rather few changes:
1. We introduce a new disk back-end type (TAP3) and a new device kind (VBD3) to
   allow blktap3 to co-exist with blktap3. blktap2 remains the default back-end
   for tap devices. Switching in the future to blktap3 as the default handler
   of tap devices should be trivial.
2. libxl doesn''t spawn the tapdisk process any more, as is the case for
   blktap2, since the tapback daemon is responsible for that. Thus, libxl only
   needs to write to XenStore the file/partition/whatever backing the virtual
   disk so that the tapback daemon can pass it to tapdisk.
3. Booting with pygrub from VHD files is trivially done by attaching blkfront
   to dom0.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>

---
Changed since v1:
  * Check whether tapback''s control socket exists instead of checking
whether
    a process named "tapback" exists.
  * Don''t duplicate code for writing the type:/path/to/file to
XenStore.

Changed since v2:
  * Support for booting from RAW and VHD images using pygrub.

We use new identifiers so that blktap2 and blktap3 can co-exist.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>

diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -58,6 +58,7 @@ libxl_disk_backend = Enumeration("disk_b
     (1, "PHY"),
     (2, "TAP"),
     (3, "QDISK"),
+    (4, "TAP3"),
     ])
 
 libxl_nic_type = Enumeration("nic_type", [
diff --git a/tools/libxl/libxl_types_internal.idl
b/tools/libxl/libxl_types_internal.idl
--- a/tools/libxl/libxl_types_internal.idl
+++ b/tools/libxl/libxl_types_internal.idl
@@ -20,6 +20,7 @@ libxl__device_kind = Enumeration("device
     (6, "VKBD"),
     (7, "CONSOLE"),
     (8, "VTPM"),
+    (9, "VBD3"),
     ])
 
 libxl__console_backend = Enumeration("console_backend", [
diff --git a/tools/libxl/libxlu_disk_l.c b/tools/libxl/libxlu_disk_l.c
--- a/tools/libxl/libxlu_disk_l.c
+++ b/tools/libxl/libxlu_disk_l.c
@@ -859,6 +859,7 @@ static void setformat(DiskParseContext *
 static void setbackendtype(DiskParseContext *dpc, const char *str) {
     if (     !strcmp(str,"phy"))   DSET(dpc,backend,BACKEND,str,PHY);
     else if (!strcmp(str,"tap"))   DSET(dpc,backend,BACKEND,str,TAP);
+    else if (!strcmp(str,"tap3"))  
DSET(dpc,backend,BACKEND,str,TAP3);
     else if (!strcmp(str,"qdisk"))
DSET(dpc,backend,BACKEND,str,QDISK);
     else xlu__disk_err(dpc,str,"unknown value for backendtype");
 }
diff --git a/tools/libxl/libxlu_disk_l.l b/tools/libxl/libxlu_disk_l.l
--- a/tools/libxl/libxlu_disk_l.l
+++ b/tools/libxl/libxlu_disk_l.l
@@ -109,6 +109,7 @@ static void setformat(DiskParseContext *
 static void setbackendtype(DiskParseContext *dpc, const char *str) {
     if (     !strcmp(str,"phy"))   DSET(dpc,backend,BACKEND,str,PHY);
     else if (!strcmp(str,"tap"))   DSET(dpc,backend,BACKEND,str,TAP);
+    else if (!strcmp(str,"tap3"))  
DSET(dpc,backend,BACKEND,str,TAP3);
     else if (!strcmp(str,"qdisk"))
DSET(dpc,backend,BACKEND,str,QDISK);
     else xlu__disk_err(dpc,str,"unknown value for backendtype");
 }

This patch implements function libxl__blktap3_enabled, the equivalent of the
existing libxl__blktap_enabled for blktap2. The checks performed are rather
simple and should be extended.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
---
Changed since v1:
  * Check whether tapback''s control socket exists instead of checking
whether
    the process exists.
  * Include the blktap3 header when compiling as this is where the path of
    tapback''s control socket is defined.

diff --git a/tools/libxl/Makefile b/tools/libxl/Makefile
--- a/tools/libxl/Makefile
+++ b/tools/libxl/Makefile
@@ -37,8 +37,11 @@ LIBXLU_LIBS  LIBXL_OBJS-y = osdeps.o libxl_paths.o
libxl_bootloader.o flexarray.o
 ifeq ($(LIBXL_BLKTAP),y)
 LIBXL_OBJS-y += libxl_blktap2.o
+LIBXL_OBJS-y += libxl_blktap3.o
+CFLAGS += -I$(XEN_ROOT)/tools/blktap3/include
 else
 LIBXL_OBJS-y += libxl_noblktap2.o
+LIBXL_OBJS-y += libxl_noblktap3.o
 endif
 LIBXL_OBJS-$(CONFIG_X86) += libxl_cpuid.o libxl_x86.o
 LIBXL_OBJS-$(CONFIG_IA64) += libxl_nocpuid.o libxl_noarch.o
diff --git a/tools/libxl/libxl_blktap3.c b/tools/libxl/libxl_blktap3.c
new file mode 100644
--- /dev/null
+++ b/tools/libxl/libxl_blktap3.c
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2012      Citrix Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ */
+
+#include "libxl_osdeps.h" /* must come before any other headers */
+#include "libxl_internal.h"
+#include <unistd.h>
+#include "blktap3.h"
+
+/*
+ * Simple sanity checks. Most of these checks are not race-free (e.g. checking
+ * wether the tapdisk binary exists), but at least we get some protection
+ * against spectacularly silly mistakes.
+ *
+ * We don''t check whether the tapdisk binary exists as this is done by
the
+ * tapback daemon.
+ */
+int libxl__blktap3_enabled(libxl__gc *gc)
+{
+    libxl_ctx *ctx = libxl__gc_owner(gc);
+    int err;
+
+    /*
+     * Check whether the tapback daemon is running.
+     */
+    err = access(TAPBACK_CTL_SOCK_PATH, F_OK);
+    if (err) {
+        if (errno != ENOENT)
+            LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
+                "failed to check whether the tapback daemon is
running\n");
+        return 0;
+    }
+
+    /*
+     * TODO Check for evtchn, gntdev. How do we do that!?
+     */
+
+    return 1;
+}
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1343,6 +1343,14 @@ struct libxl__cpuid_policy {
 };
 
 /*
+ * blktap3 support
+ */
+/* libxl__blktap_enabled:
+ *    return true if blktap3 support is available.
+ */
+_hidden int libxl__blktap3_enabled(libxl__gc *gc);
+
+/*
  * blktap2 support
  */
 
diff --git a/tools/libxl/libxl_noblktap3.c b/tools/libxl/libxl_noblktap3.c
new file mode 100644
--- /dev/null
+++ b/tools/libxl/libxl_noblktap3.c
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2012      Citrix Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ */
+
+#include "libxl_osdeps.h" /* must come before any other headers */
+#include "libxl_internal.h"
+
+int libxl__blktap3_enabled(libxl__gc *gc)
+{
+    return 0;
+}

Handling of blktap3 devices is similar to blktap2, except that libxl
doesn''t
spawn the tapdisk and doesn''t create the physical device in dom0.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>

---
Changed since v1:
  * Don''t duplicate code for writing the type:/path/to/file to
XenStore.
Changed since v2:
  * Fixed a warning in libxl when destroying a blktap3-based domain.
  * Removed TODO comment regarding scripts.

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -1159,6 +1159,8 @@ static void disk_eject_xswatch_callback(
         disk->backend = LIBXL_DISK_BACKEND_TAP;
     } else if (!strcmp(backend_type, "qdisk")) {
         disk->backend = LIBXL_DISK_BACKEND_QDISK;
+    } else if (!strcmp(backend_type, "tap3")) {
+        disk->backend = LIBXL_DISK_BACKEND_TAP3;
     } else {
         disk->backend = LIBXL_DISK_BACKEND_UNKNOWN;
     }
@@ -2013,6 +2015,9 @@ int libxl__device_from_disk(libxl__gc *g
         case LIBXL_DISK_BACKEND_QDISK:
             device->backend_kind = LIBXL__DEVICE_KIND_QDISK;
             break;
+        case LIBXL_DISK_BACKEND_TAP3:
+            device->backend_kind = LIBXL__DEVICE_KIND_VBD3;
+            break;
         default:
             LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "unrecognized disk backend
type: %d\n",
                        disk->backend);
@@ -2138,11 +2143,15 @@ static void device_disk_add(libxl__egc *
 
                 /* now create a phy device to export the device to the guest */
                 goto do_backend_phy;
+            case LIBXL_DISK_BACKEND_TAP3:
             case LIBXL_DISK_BACKEND_QDISK:
                 flexarray_append(back, "params");
                 flexarray_append(back, libxl__sprintf(gc, "%s:%s",
                              
libxl__device_disk_string_of_format(disk->format), disk->pdev_path));
-                assert(device->backend_kind == LIBXL__DEVICE_KIND_QDISK);
+                assert(
+                        (disk->backend == LIBXL_DISK_BACKEND_QDISK
+                         && device->backend_kind ==
LIBXL__DEVICE_KIND_QDISK)
+                        || (disk->backend == LIBXL_DISK_BACKEND_TAP3));
                 break;
             default:
                 LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "unrecognized disk
backend type: %d\n", disk->backend);
diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -218,6 +218,22 @@ static int disk_try_backend(disk_try_bac
         }
         return backend;
 
+    case LIBXL_DISK_BACKEND_TAP3:
+        if (a->disk->script) goto bad_script;
+
+        if (!libxl__blktap3_enabled(a->gc)) {
+            LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "Disk vdev=%s, backend
tap"
+                       " unsuitable because blktap3 not available",
+                       a->disk->vdev);
+            return 0;
+        }
+        /* TODO other formats supported by blktap3? */
+        if (!(a->disk->format == LIBXL_DISK_FORMAT_RAW ||
+              a->disk->format == LIBXL_DISK_FORMAT_VHD)) {
+            goto bad_format;
+        }
+        return backend;
+
     case LIBXL_DISK_BACKEND_QDISK:
         if (a->disk->script) goto bad_script;
         return backend;
@@ -289,6 +305,7 @@ int libxl__device_disk_set_backend(libxl
         ok             disk_try_backend(&a, LIBXL_DISK_BACKEND_PHY) ?:
             disk_try_backend(&a, LIBXL_DISK_BACKEND_TAP) ?:
+            disk_try_backend(&a, LIBXL_DISK_BACKEND_TAP3) ?:
             disk_try_backend(&a, LIBXL_DISK_BACKEND_QDISK);
         if (ok)
             LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "Disk vdev=%s, using backend
%s",
@@ -321,6 +338,7 @@ char *libxl__device_disk_string_of_backe
     switch (backend) {
         case LIBXL_DISK_BACKEND_QDISK: return "qdisk";
         case LIBXL_DISK_BACKEND_TAP: return "phy";
+        case LIBXL_DISK_BACKEND_TAP3: return "phy";
         case LIBXL_DISK_BACKEND_PHY: return "phy";
         default: return NULL;
     }
@@ -790,7 +808,8 @@ void libxl__initiate_device_remove(libxl
             goto out;
         }
         return;
-    }
+    } else if (aodev->dev->backend_kind == LIBXL__DEVICE_KIND_VBD3)
+        goto out;
 
     for (;;) {
         rc = libxl__xs_transaction_start(gc, &t);

This patch allows guests to boot from RAW and VHD images using pygrub.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>

diff --git a/tools/blktap3/drivers/tapdisk-control.c
b/tools/blktap3/drivers/tapdisk-control.c
--- a/tools/blktap3/drivers/tapdisk-control.c
+++ b/tools/blktap3/drivers/tapdisk-control.c
@@ -910,7 +910,7 @@ tapdisk_control_xenblkif_connect(
     assert(request);
     assert(response);
 
-    len = strnlen(request->u.string.text, TAPDISK_MESSAGE_STRING_LENGTH);
+    len = strnlen(request->u.blkif.params, TAPDISK_MESSAGE_STRING_LENGTH);
     /* TODO boilerplate */
     if (len < 1) {
         err = -EINVAL;
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2636,6 +2636,7 @@ void libxl__device_disk_local_initiate_a
             }
             break;
         case LIBXL_DISK_BACKEND_QDISK:
+        case LIBXL_DISK_BACKEND_TAP3:
             if (disk->format != LIBXL_DISK_FORMAT_RAW) {
                 libxl__prepare_ao_device(ao, &dls->aodev);
                 dls->aodev.callback = local_device_attach_cb;
@@ -2728,6 +2729,7 @@ void libxl__device_disk_local_initiate_d
 
     switch (disk->backend) {
         case LIBXL_DISK_BACKEND_QDISK:
+        case LIBXL_DISK_BACKEND_TAP3:
             if (disk->vdev != NULL) {
                 GCNEW(device);
                 rc = libxl__device_from_disk(gc, LIBXL_TOOLSTACK_DOMID,
diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -753,8 +753,8 @@ void libxl__wait_device_connection(libxl
          */
         device_hotplug(egc, aodev);
         return;
-    }
-
+    } else if (aodev->dev->backend_kind == LIBXL__DEVICE_KIND_VBD3)
+        goto out;
     rc = libxl__ev_devstate_wait(gc, &aodev->backend_ds,
                                  device_backend_callback,
                                  state_path, XenbusStateInitWait,