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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-04-23 at 10:36 +0100, 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 (assumed to be 0)

AKA LIBXL_TOOLSTACK_DOMID. That line could also do with wrapping but I
can do that as I commit if you like.

>  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, 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@xxxxxxxxxxxxx>

With the above changes:

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

> ---
>  tools/libxl/libxl_device.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
> index eeea9d9..ec0fec2 100644
> --- a/tools/libxl/libxl_device.c
> +++ b/tools/libxl/libxl_device.c
> @@ -236,7 +236,7 @@ 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 == 0 && !disk->script) {
>          if (stat(disk->pdev_path, &a.stab)) {
>              LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "Disk vdev=%s "
>                               "failed to stat: %s",



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