Support Ceph mount using DNS name

[KarlJorgensen]

Case in point: For Ceph file systems, the mount command can look like this:

mount -t ceph -o mds_namespace=ns1,name=ovirt,secret=xxx monitors.storage.example.com:/ /mnt

but the resulting entry in /proc/mounts will NOT look identical, as ceph will resolve DNS names into their IP addresses:

192.168.1.5,192.168.1.6,192.168.1.7:/ /mnt ceph rw,seclabel,relatime,name=ovirt,secret=<hidden>,acl,mds_namespace=ovirt 0 0

(in this example monitors.storage.example.com was a DNS entry
resolving to 3 IP addresses).

Lesson learned: We cannot rely on mount options being carried
unmolested into /proc/mounts...

Bug-Url: https://bugzilla.redhat.com/1995610

[nirs]

There are 2 issues with this change:

1. It affects all kinds of mounts to solve a ceph specific issue. We need a fix that does not change the system behavior with other mounts.
2. Even for ceph mount, this is incorrect. With this change if you have 2 ceph mounts, one mounted and one not, mounting the second mount will fail since we will consider it as mounted, comparing only the remote file part "/", which is same in both mounts.

I think that what we learn from this is not that we cannot expect to find the mount options in /proc/mounts, but that we cannot work with ceph mounts since they behave in a non-standard way.

We need a way to detect if a mount is mounted. The current code accept a "server:path" format and mount it at /rhev/data-center/mnt/srever:path. Since mounts can become stale, and can be unmounted, we must make sure that /rhev/data-center/mnt/srever:path is mounted, and that the remove server and path match.

In summary, a fix must not change anything for other storage, and provide a good way to match the mount with the server:path. A possible solution can be resolving the DNS name before the mount so the local mount path will match /proc/mounts. Or maybe a change in ceph to disable resolving before the mount.

This change also break the tests:
https://github.com/oVirt/vdsm/actions/runs/2192442081