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

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

[David Scott]

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)
 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@eu.citrix.com>
---
 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",
-- 
1.8.1.2

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

[Ian Campbell]

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@eu.citrix.com>

With the above changes:

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

> ---
>  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",

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

[David Scott]

On 23/04/13 10:44, Ian Campbell wrote:
> 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.

Ah, I grepped around for stuff like "DOMID_SELF" but missed that one :-)

I'll resend...

Cheers,
Dave