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

[Blue Swirl]

On Fri, Jun 18, 2010 at 6:38 PM, Ryan Harper <address@hidden> wrote:
> 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;

I'd change this to:
static inline ssize_t serial_sysfs(char *d, const char *s, ssize_t n)
{
       const 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 
> *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
>
>
>