[libvirt] [PATCH] rbd: Open in Read-Only mode when refreshing a volume

[Wido den Hollander]

By opening a RBD volume in Read-Only we do not register a
watcher on the header object inside the Ceph cluster.

Refreshing a volume only calls rbd_stat() which is a operation
which does not write to a RBD image.

This allows us to use a cephx user which has no write
permissions if we would want to use the libvirt storage pool
for informational purposes only.

It also saves us a write into the Ceph cluster which should
speed up refreshing a RBD pool.

rbd_open_read_only() is available in all librbd versions which
also support rbd_open().

Signed-off-by: Wido den Hollander <wido at widodh.nl>
---
 src/storage/storage_backend_rbd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/storage/storage_backend_rbd.c b/src/storage/storage_backend_rbd.c
index 8c7a80d..3ab7912 100644
--- a/src/storage/storage_backend_rbd.c
+++ b/src/storage/storage_backend_rbd.c
@@ -283,7 +283,7 @@ static int volStorageBackendRBDRefreshVolInfo(virStorageVolDefPtr vol,
     int r = 0;
     rbd_image_t image = NULL;
 
-    r = rbd_open(ptr->ioctx, vol->name, &image, NULL);
+    r = rbd_open_read_only(ptr->ioctx, vol->name, &image, NULL);
     if (r < 0) {
         ret = -r;
         virReportSystemError(-r, _("failed to open the RBD image '%s'"),
-- 
1.9.1