Should journaled quota be default for ext4?
Ted's email about quotacheck made me think:
Is there a reason that journaled quota is not default for ext4? (or ext3 for that matter, but we're not messing with that now)
IOW - if we do mount -o quota, is there any reason that we should also need more options to journal that quota? When would we not want journaled quota?
(Forgive me if it's a dumb question, I'm not as well versed in extN quota as I probably should be).
-Eric
Quoted 11 lines · Eric Sandeen
Ted's email about quotacheck made me think:
Is there a reason that journaled quota is not default for ext4? (or ext3 for that matter, but we're not messing with that now)
IOW - if we do mount -o quota, is there any reason that we should also need more options to journal that quota? When would we not want journaled quota?
(Forgive me if it's a dumb question, I'm not as well versed in extN quota as I probably should be).
Part of the problem is that these mount options matter to various init scripts (and possibly to quotatools?). So for example, the usrquota and grpquota mount options are complete no-ops as far as the kernel code is concerned. But they are there so they show up in /proc/mounts, just in case /etc/mtab is a symlink to /proc/mounts (as it is in some setups), because userspace scripts/tools care about knowing whether the user wanted user or group quotas. (And I think the reason for that is because if someone only wants user or group quotas, it's cheaper/faster if we only do the form of quota that is required by the sysadmin....)
Worse yet, not all the distributions are standardized using the same init scripts.
I *think* ditching non-journal quota does simplify things immensely, but we will need to collect init scripts (and possibly private patches to quotatools) across multiple distributions in order to be sure.
(I was looking at this, as well as the documentation out there on the net about how to use quotas, and it's a bit of a mess. :-/ )
- Ted
Quoted 10 lines · Eric Sandeen
Quoted 9 lines
Ted's email about quotacheck made me think:
Is there a reason that journaled quota is not default for ext4? (or ext3 for that matter, but we're not messing with that now)
IOW - if we do mount -o quota, is there any reason that we should also need more options to journal that quota? When would we not want journaled quota?
Quoted 5 lines
Quoted 2 lines
(Forgive me if it's a dumb question, I'm not as well versed in extN quota as I probably should be).
Part of the problem is that these mount options matter to various init scripts (and possibly to quotatools?). So for example, the usrquota
Yes, quota-tools currently use these options as well to detect whether they
should run the command on the filesystem or not. The problem is that at least "quotaon -a" needs to know on which filesystem it should run and currently it uses quota mount options to decide. I can change quota tools to just look for quota files but that's not guaranteed to succeed because for unjournaled quotas, quota files could be anywhere - even on a different filesystem - and I really know admins who use such setup. And for journaled quotas, file name of the quota file is the one given in the {usr,grp}jquota mount option so without it it's impossible to locate the quota file as well.
So I think the easiest way out of this is really to make quota files hidden
as we discussed in another thread. Then kernel always knows whether the filesystem accounts quotas or not and quota tools can ask it with GETFMT quotactl.
Honza
Signature · 2 lines
Jan Kara <[email protected]> SuSE CR Labs
Quoted 7 lines · Jan Kara
Yes, quota-tools currently use these options as well to detect whether they
should run the command on the filesystem or not. The problem is that at least "quotaon -a" needs to know on which filesystem it should run and currently it uses quota mount options to decide. I can change quota tools to just look for quota files but that's not guaranteed to succeed because for unjournaled quotas, quota files could be anywhere - even on a different filesystem - and I really know admins who use such setup.
Hmm.... so is this something we need to continue to support? If we phase out support for anything other than hidden journal files, that implies that these sysadmins would eventually need to ove, right?
Quoted 3 lines
And for journaled quotas, file name
of the quota file is the one given in the {usr,grp}jquota mount option so without it it's impossible to locate the quota file as well.
... and sometimes names other than aquota.user and aquota.group are used? I was thinking about having e2fsck look for those file names, maybe check the format, and then offer to auto-convert them to the new format with hidden quota files. I suppose I could have e2fsck try to look for that information in /etc/fstab, but that adds a different layer of complexity (namely, we need to be confident we can match up a particular device with an /etc/fstab entry, which usually but doesn't always work).
Quoted 4 lines
So I think the easiest way out of this is really to make quota
files hidden as we discussed in another thread. Then kernel always knows whether the filesystem accounts quotas or not and quota tools can ask it with GETFMT quotactl.
I agreee, long term that will be the right answer.
I just realized that since ext4 does support a nojournal mode, we will also need to support a no-journal mode with the hidden quota file, but that's not a big deal if e2fsck handles checking the file system consistency as well as rebuilding the quota in-use information for the hidden quota file.
- Ted
Quoted 9 lines · Jan Kara
Quoted 7 lines
Yes, quota-tools currently use these options as well to detect whether they
should run the command on the filesystem or not. The problem is that at least "quotaon -a" needs to know on which filesystem it should run and currently it uses quota mount options to decide. I can change quota tools to just look for quota files but that's not guaranteed to succeed because for unjournaled quotas, quota files could be anywhere - even on a different filesystem - and I really know admins who use such setup.
Quoted 3 lines
Hmm.... so is this something we need to continue to support? If we phase out support for anything other than hidden journal files, that implies that these sysadmins would eventually need to ove, right?
Yes, they will be forced to move. Honestly, I never heard a good technical
reason for this so hopefully it won't be a big pain for them. But sure we have to provide a long enough period where we only warn about deprecation so that we can get some decent feedback.
Quoted 6 lines
Quoted 3 lines
And for journaled quotas, file name
of the quota file is the one given in the {usr,grp}jquota mount option so without it it's impossible to locate the quota file as well.... and sometimes names other than aquota.user and aquota.group are used?
Sadly yes, although I expect this to be rather rare.
Quoted 6 lines
I was thinking about having e2fsck look for those file names, maybe check the format, and then offer to auto-convert them to the new format with hidden quota files. I suppose I could have e2fsck try to look for that information in
/etc/fstab, but that adds a different layer of complexity (namely, we need to be confident we can match up a particular device with an/etc/fstabentry, which usually but doesn't always work).
Alternatively, you could have an option where admin could provide filenames
of quota files for conversion if e2fsck cannot find them on its own. It wouldn't be automated but it would still provide a reasonable transition path.
Honza
Signature · 2 lines
Jan Kara <[email protected]> SuSE CR Labs