Linux Virtualization - Jun 2010 - [PATCH 0/2] v2: Add 'serial' attribute to virtio-blk devices

Using Rusty's suggestion I've respun the patch removing the special copy
function.  I've tested this patch in a guest kernel with and without qemu
supplying serial numbers for the block devices and it's working as expected.
When qemu supplies serial numbers, the correct value is supplied to
/sys/block/vdX/serial and can be used by udev for generating disk/by-id paths
(without separate utility).  When running without serial number support the path
still exists in sysfs but produces no output.

Signed-off-by: Ryan Harper <ryanh at us.ibm.com>

Create a new attribute for virtio-blk devices that will fetch the serial number
of the block device.  This attribute can be used by udev to create disk/by-id
symlinks for devices that don't have a UUID (filesystem) associated with
them.

ATA_IDENTIFY strings are special in that they can be up to 20 chars long
and aren't required to be nul-terminated.  The buffer is also zero-padded
meaning that if the serial is 19 chars or less that we get a nul-terminated
string.  When copying this value into a string buffer, we must be careful to
copy up to the nul (if it present) and only 20 if it is longer and not to
attempt to nul terminate; this isn't needed.

Changes since v1:
- Added BUILD_BUG_ON() for PAGE_SIZE check
- Removed min() since BUILD_BUG_ON() handles the check
- Replaced serial_sysfs() by copying id directly to buffer

Signed-off-by: Ryan Harper <ryanh at us.ibm.com>
Signed-off-by: john cooper <john.cooper at redhat.com>
---
 drivers/block/virtio_blk.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 258bc2a..34411ff 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -281,6 +281,27 @@ static int index_to_minor(int index)
 	return index << PART_BITS;
 }
 
+static ssize_t virtblk_serial_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	int err;
+
+	/* sysfs gives us a PAGE_SIZE buffer */
+	BUILD_BUG_ON(PAGE_SIZE < VIRTIO_BLK_ID_BYTES);
+
+	buf[VIRTIO_BLK_ID_BYTES] = '\0';
+	err = virtblk_get_id(disk, buf);
+	if (!err)
+		return strlen(buf);
+
+	if (err == -EIO) /* Unsupported? Make it empty. */
+		return 0;
+
+	return err;
+}
+DEVICE_ATTR(serial, S_IRUGO, virtblk_serial_show, NULL);
+
 static int __devinit virtblk_probe(struct virtio_device *vdev)
 {
 	struct virtio_blk *vblk;
@@ -445,8 +466,15 @@ static int __devinit virtblk_probe(struct virtio_device
*vdev)
 
 
 	add_disk(vblk->disk);
+	err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial);
+	if (err)
+		goto out_del_disk;
+
 	return 0;
 
+out_del_disk:
+	del_gendisk(vblk->disk);
+	blk_cleanup_queue(vblk->disk->queue);
 out_put_disk:
 	put_disk(vblk->disk);
 out_mempool:
-- 
1.6.3.3

With the availablility of a sysfs device attribute for examining disk serial
numbers the ioctl is no longer needed.  The user-space changes for this
aren't
upstream yet so we don't have any users to worry about.

Signed-off-by: Ryan Harper <ryanh at us.ibm.com>
---
 drivers/block/virtio_blk.c |   10 ----------
 1 files changed, 0 insertions(+), 10 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 34411ff..04458cd 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -225,16 +225,6 @@ static int virtblk_ioctl(struct block_device *bdev, fmode_t
mode,
 	struct gendisk *disk = bdev->bd_disk;
 	struct virtio_blk *vblk = disk->private_data;
 
-	if (cmd == 0x56424944) { /* 'VBID' */
-		void __user *usr_data = (void __user *)data;
-		char id_str[VIRTIO_BLK_ID_BYTES];
-		int err;
-
-		err = virtblk_get_id(disk, id_str);
-		if (!err && copy_to_user(usr_data, id_str, VIRTIO_BLK_ID_BYTES))
-			err = -EFAULT;
-		return err;
-	}
 	/*
 	 * Only allow the generic SCSI ioctls if the host can support it.
 	 */
-- 
1.6.3.3

On Thu, 24 Jun 2010 12:49:56 pm Ryan Harper wrote:
> Using Rusty's suggestion I've respun the patch removing the special
copy
> function.  I've tested this patch in a guest kernel with and without
qemu
> supplying serial numbers for the block devices and it's working as
expected.
> When qemu supplies serial numbers, the correct value is supplied to
> /sys/block/vdX/serial and can be used by udev for generating disk/by-id
paths
> (without separate utility).  When running without serial number support the
path
> still exists in sysfs but produces no output.
> 
> Signed-off-by: Ryan Harper <ryanh at us.ibm.com>
Great, both applied.

BTW, a mail without a patch doesn't need a sign off, does it?

Thanks,
Ruty.