[Xen-devel] [PATCH v7] libxl: allow 'phy' backend to use empty files

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

This was introduced by 97ee1f (~5 years ago), but was probably never
surfaced because most people used regular files as CDROM images, so the PHY
backend was actually never selected. A year ago this was changed, and now
regular RAW files are also handled by the PHY backend, which has made this
bug suface.

Fix it by allowing empty disks to use the PHY backend, skipping the stat
tests.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Reported-by: Alex Braunegg <alex.braunegg@xxxxxxxxx>
---
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Alex Braunegg <alex.braunegg@xxxxxxxxx>
---
Changes since v6:
 - Turn the assert into a check at libxl__device_disk_set_backend.

Changes since v4:
 - Split form the rest of the series.
 - Fix disk_try_backend.
---
 tools/libxl/libxl_device.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index 8bb5e93..e0a81e3 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -196,6 +196,12 @@ static int disk_try_backend(disk_try_backend_args *a,
             goto bad_format;
         }
 
+        if (a->disk->format == LIBXL_DISK_FORMAT_EMPTY) {
+            LOG(DEBUG, "Disk vdev=%s is empty, skipping physical device check",
+                a->disk->vdev);
+            return backend;
+        }
+
         if (a->disk->backend_domid != LIBXL_TOOLSTACK_DOMID) {
             LOG(DEBUG, "Disk vdev=%s, is using a storage driver domain, "
                        "skipping physical device check", a->disk->vdev);
@@ -273,6 +279,12 @@ int libxl__device_disk_set_backend(libxl__gc *gc, 
libxl_device_disk *disk) {
             LOG(ERROR, "Disk vdev=%s is empty but not cdrom", disk->vdev);
             return ERROR_INVAL;
         }
+        if (disk->pdev_path != NULL && strcmp(disk->pdev_path, "")) {
+            LOG(ERROR,
+                "Disk vdev=%s is empty but an image has been provided: %s",
+                disk->vdev, disk->pdev_path);
+            return ERROR_INVAL;
+        }
         memset(&a.stab, 0, sizeof(a.stab));
     } else if ((disk->backend == LIBXL_DISK_BACKEND_UNKNOWN ||
                 disk->backend == LIBXL_DISK_BACKEND_PHY) &&
-- 
2.5.4 (Apple Git-61)


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