From: Wido den Hollander <wido@widodh.nl>
Date: Thu, 28 Jan 2016 10:20:23 +0000 (+0100)
Subject: rbd: Open in Read-Only mode when refreshing a volume
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=84678267e4bf292123250b9fe363485db3848360;p=libvirt.git

rbd: Open in Read-Only mode when refreshing a volume

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@widodh.nl>
---

diff --git a/src/storage/storage_backend_rbd.c b/src/storage/storage_backend_rbd.c
index 6a6f82160e..80a1d339fa 100644
--- a/src/storage/storage_backend_rbd.c
+++ b/src/storage/storage_backend_rbd.c
@@ -284,7 +284,7 @@ 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'"),