linux-ext4 - Re: [PATCH] ext4: Always journal quota file modifications

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Message-ID: <20100603171058.GC13179@thunk.org>
Date:	Thu, 3 Jun 2010 13:10:58 -0400
From:	tytso@....edu
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Always journal quota file modifications

On Thu, Jun 03, 2010 at 04:19:48PM +0200, Jan Kara wrote:
> > All of these problems go away if the quota file isn't visible from
> > userspace, and it becomes a special file.  In the short term I think
> > we could make this change, but I think we would also have to (1) treat
> > the quota file as immutable while quotas are enabled (so it cannot be
> > opened for writing), (2) force an fsync of the quota file and a
> > journal commit before enabling quotas, and (3) force a journal commit
> > after disabling quotas.
>   Ted, that's what generic quota code actually does for you (unless
> DQUOT_QUOTA_SYS_FILE flag is specified but that's not the case of ext?)
> - see vfs_load_quota_inode. We do:
> sync_filesystem(sb);
> invalidate_bdev(sb->s_bdev);
> ..
> inode->i_flags |= S_NOQUOTA | S_NOATIME | S_IMMUTABLE;
> ..
>   So unless someone tries to screw us really hard, we should be fine.

That's good to hear.  I think though we also need to call
sync_filesystem(sb) in dquot_disable().  Currently it calls
sb->s_op->sync_fs(), which forces out the superblock, and
sync_blockdev() which forces out any dirty buffer heads, but it
doesn't actually force a journal commit so that any pending journaled
writes to the quota file are forced out.  We need to either explicitly
sync the quota files, or use sync_filesystem(sb) and sync everything.
The former might be more polite; in fact it might be sufficient in
vfs_load_quota_inode() as well?  Or am I missing something?

		       	  	       - Ted
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