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[Qemu-devel] [PATCH 1/2] Add 'serial' attribute to virtio-blk devices

From: Ryan Harper
Subject: [Qemu-devel] [PATCH 1/2] Add 'serial' attribute to virtio-blk devices
Date: Fri, 18 Jun 2010 13:38:02 -0500

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

Signed-off-by: Ryan Harper <address@hidden>
Signed-off-by: john cooper <address@hidden>
 drivers/block/virtio_blk.c |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 258bc2a..f1ef26f 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -281,6 +281,31 @@ static int index_to_minor(int index)
        return index << PART_BITS;
+/* Copy serial number from *s to *d.  Copy operation terminates on either
+ * encountering a nul in *s or after n bytes have been copied, whichever
+ * occurs first.  *d is not forcibly nul terminated.  Return # of bytes copied.
+ */
+static inline int serial_sysfs(char *d, char *s, int n)
+       char *di = d;
+       while (*s && n--)
+               *d++ = *s++;
+       return d - di;
+static ssize_t virtblk_serial_show(struct device *dev,
+                               struct device_attribute *attr, char *buf)
+       struct gendisk *disk = dev_to_disk(dev);
+       char id_str[VIRTIO_BLK_ID_BYTES];
+       if (IS_ERR(virtblk_get_id(disk, id_str)))
+               return 0;
+       return serial_sysfs(buf, id_str, min(VIRTIO_BLK_ID_BYTES, PAGE_SIZE));
+DEVICE_ATTR(serial, S_IRUGO, virtblk_serial_show, NULL);
 static int __devinit virtblk_probe(struct virtio_device *vdev)
        struct virtio_blk *vblk;
@@ -445,8 +470,15 @@ static int __devinit virtblk_probe(struct virtio_device 
+       err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial);
+       if (err)
+               goto out_del_disk;
        return 0;
+       del_gendisk(vblk->disk);
+       blk_cleanup_queue(vblk->disk->queue);

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