Bug 765474 (GLUSTER-3742)

Summary: Mount option "ro" (read only) is not reported by 'mount' command
Product: [Community] GlusterFS Reporter: Louis Zuckerman <glusterbugs>
Component: fuseAssignee: Kaushal <kaushal>
Status: CLOSED CURRENTRELEASE QA Contact:
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Priority: medium    
Version: mainlineCC: csaba, gluster-bugs, vijay
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Hardware: x86_64   
OS: Linux   
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Description Louis Zuckerman 2011-10-19 22:55:02 UTC 
Mounting a glusterfs volume with option "ro" (read only) works correctly, but when mounts are printed using the 'mount' command the mount option "rw" (read/write) appears where "ro" should be.

To reproduce:

# mount -t glusterfs localhost:test /mnt/test -o ro

# touch /mnt/test/write
touch: cannot touch `/mnt/test/write': Read-only file system

# mount
...
localhost:test on /mnt/test type fuse.glusterfs (rw,allow_other,default_permissions,max_read=131072)

Even though the mount is clearly read-only, it is reported as being writable.

Thanks!
Comment 1 Csaba Henk 2011-11-03 21:00:37 UTC 
(In reply to comment #0)
> Mounting a glusterfs volume with option "ro" (read only) works correctly, but
> when mounts are printed using the 'mount' command the mount option "rw"
> (read/write) appears where "ro" should be.

While I agree that this is confusing, both the behavior and the mount output is correct. The "ro" or "rw" flags reported by mount(8) means a _kernel-level_ read-only / read-writable mode. Glusterfs' read-only mode is not implemented at the kernel level, but within the software.

What we could possibly do to fight the confusion:

- introduce a "-oread_only" mount option in mount.glusterfs mount helper which maps to glusterfs' "--read-only" option; keep existing "-oro" but make it deprecated (ie. give a deprecation warning and point to -oread_only if used). This way we can move away from abusing "-oro", which is indeed documented to refer to kernel-level read-onliness (cf. mount(8)).
- make it clear in documentation that we implement read-only mode in our scope
- add a  "gluster mount" command which is analogous to mount(8) but is restricted to glusterfs mounts and displays glusterfs specific informations -- like read-onliness

@kaushal: please comment which approach(es) you prefer (feel free to prefer something different than my above ideas).
Comment 2 Kaushal 2011-11-04 02:38:00 UTC 
Csaba,
Among the 3 approaches, I believe the gluster specific mount command would be the best. The other two, while easier to do, might lead to more confusion in users.

I also have a question. Would it cause any problems if kernel ro mode and gluster ro mode are in use? I've submitted a patch for review (review.gluster.com/655), that causes the kernel ro mode to be enabled when mounting gluster in read-only. This seems to solve the problem.
Comment 3 Csaba Henk 2011-11-09 16:25:56 UTC 
(In reply to comment #2)
Sure, this is the most straightforward approach, and then we can forget of the 3 approaches which I found out to wrap up the conceptual difference (so now, we rather just eliminate conceptual differences ;)).

Kernel-level ro as such is completely fine, what I had a problem with was the redundancy of the twofold ro.
Comment 4 Anand Avati 2011-11-23 00:46:14 UTC 
CHANGE: http://review.gluster.com/655 (Enables kernel read-only mode on mounting with '-oro' and disables the gluster) merged in master by Vijay Bellur (vijay)