Re: [PATCH v2] Only call stat() when adding a disk if we expect a device to exist.

["Roger Pau Monné" <roger.pau@citrix.com>]

On 23/04/13 11:59, David Scott wrote:
> We consider calling stat() a helpful error check in the following
> circumstances only:
>  1. the disk backend type must be PHYsical
>  2. the disk backend domain must be the same as the running libxl
>     code (ie LIBXL_TOOLSTACK_DOMID)
>  3. there must not be a hotplug script because this would imply that
>     the device won't be created until after the hotplug script has
>     run.
> 
> With this fix, it is possible to use qemu's built-in block drivers
> such as ceph/rbd, with a xl config disk spec like this:
> 
> disk=[ 'backendtype=qdisk,format=raw,vdev=hda,access=rw,target=rbd:rbd/ubuntu1204.img' ]
> 
> Signed-off-by: David Scott <dave.scott@eu.citrix.com>
> Acked-by: Ian Campbell <ian.campbell@citrix.com>

Acked-by: Roger Pau Monné <roger.pau@citrix.com>

> ---
>  tools/libxl/libxl_device.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
> index eeea9d9..eb60fd5 100644
> --- a/tools/libxl/libxl_device.c
> +++ b/tools/libxl/libxl_device.c
> @@ -236,7 +236,9 @@ int libxl__device_disk_set_backend(libxl__gc *gc, libxl_device_disk *disk) {
>              return ERROR_INVAL;
>          }
>          memset(&a.stab, 0, sizeof(a.stab));
> -    } else if (!disk->script) {
> +    } else if (disk->backend == LIBXL_DISK_BACKEND_PHY &&
> +               disk->backend_domid == LIBXL_TOOLSTACK_DOMID &&
> +               !disk->script) {
>          if (stat(disk->pdev_path, &a.stab)) {
>              LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "Disk vdev=%s "
>                               "failed to stat: %s",
>