Mounting a Glusterfs volume with read only option in /etc/fstab fails

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 5, 6
  • Red Hat Storage Server 2.0
  • GlusterFS native client

Issue

  • It is not possible to mount a Red Hat Storage volume read-only through the GlusterFS native client. The configuration in /etc/fstab includes ro in the mount options:
$ grep glusterfs /etc/fstab
rh-storage:/test        /shared/test            glusterfs ro,_netdev  0 0
  • Mounting fails with an error like this:
$ mount /shared/test
Mount failed. Please check the log file for more details.

Resolution

  • Red Hat Storage 2.0 native clients on Red Hat Enterprise Linux 6

  • Red Hat Storage 2.0 native clients on Red Hat Enterprise Linux 5

    • Update the client to Red Hat Storage 2.1 enhancement and bug fix update #1 (RHBA-2013:1769-1) or newer.

Root Cause

  • The GlusterFS native client does not support mounting volumes read-only anymore. This is not intentional and a regression compared to the Red Hat Software Storage Appliance 3.2 (RHSSA-3.2), the previous release of a Red Hat product containing GlusterFS.

  • A patch was posted for review. With this patch the GlusterFS native client (which uses FUSE) regains support for read-only mounting of Red Hat Storage volumes. An additional patch has been proposed to fix the issue in RHEL-5 as well.

Diagnostic Steps

  • Reproducing the issue on RHEL-5:
[root@vm-61 ~]# mount -t glusterfs -o ro storage-1:/test-vol /mnt
[root@vm-61 ~]# grep test-vol /proc/mounts
glusterfs#storage-1:/test-vol /mnt fuse rw,user_id=0,group_id=0,default_permissions,allow_other,max_read=131072 0 0
[root@vm-61 ~]# mount | grep test-vol
glusterfs#storage-1:/test-vol on /mnt type fuse (ro,default_permissions,allow_other,max_read=131072)
[root@vm-61 ~]# ps ax | grep glusterfs
 2427 ?        Ssl    0:00 /usr/sbin/glusterfs --read-only --volfile-id=/test-vol --volfile-server=storage-1 /mnt
[root@vm-61 ~]# touch /mnt/hello
[root@vm-61 ~]# rm -f /mnt/hello
  • Note that /proc/mounts shows "rw" as option, not "ro".
$ strace -f -e mount /usr/sbin/glusterfs --log-level=TRACE --read-only --volfile-id=/test-vol --volfile-server=storage-1 /mnt
1983  mount("storage-1:/test-vol", "/mnt", "fuse.glusterfs", MS_RDONLY, "default_permissions,allow_other,") = -1 ENODEV (No such device)
1983  mount("glusterfs#storage-1:/test-vol", "/mnt", "fuse", 0, "default_permissions,allow_other,") = 0

  • The first mount() fails, and the second with a little different format works. But, the second does not pass the MS_RDONLY flag.

  • The matching code is in contrib/fuse-lib/mount.c:

536         ret = mount (source, mountpoint, fstype, mountflags,
537                      mnt_param_mnt);
538         if (ret == -1 && errno == ENODEV) {
539                 /* fs subtype support was added by 79c0b2df aka
540                    v2.6.21-3159-g79c0b2d. Probably we have an
541                    older kernel ... */
542                 fstype = "fuse";
543                 ret = asprintf (&source, "glusterfs#%s", fsname);
...
549                 ret = mount (source, mountpoint, fstype, 0,
550                              mnt_param_mnt);
551         }
  • Note the mount() syscall on line 549, the mountflags are not passed like it is done on line 536.

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