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

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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>
This commit is contained in:
Wido den Hollander 2016-01-28 11:20:23 +01:00 committed by John Ferlan
parent 0b15f92032
commit 84678267e4
1 changed files with 1 additions and 1 deletions
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2
src/storage/storage_backend_rbd.c
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@ -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'"),