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Re: [PATCH] xfs: Initialize all quota inodes to be NULLFSINO

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: Initialize all quota inodes to be NULLFSINO
From: Chandra Seetharaman <sekharan@xxxxxxxxxx>
Date: Wed, 17 Jul 2013 16:42:10 -0500
Cc: XFS mailing list <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130716002352.GA3920@dastard>
Organization: IBM
References: <1373593665.20769.10.camel@xxxxxxxxxxxxxxxxxx> <20130713021349.GH3438@dastard> <1373928885.20769.42.camel@xxxxxxxxxxxxxxxxxx> <20130716002352.GA3920@dastard>
Reply-to: sekharan@xxxxxxxxxx
On Tue, 2013-07-16 at 10:23 +1000, Dave Chinner wrote:
> On Mon, Jul 15, 2013 at 05:54:45PM -0500, Chandra Seetharaman wrote:
> > On Sat, 2013-07-13 at 12:13 +1000, Dave Chinner wrote:
> > > On Thu, Jul 11, 2013 at 08:47:45PM -0500, Chandra Seetharaman wrote:
> > > > 
> > > > mkfs doesn't initialize the quota inodes to NULLFSINO as it
> > > > does for the other internal inodes. This leads to check for two
> > > > values (0 and NULLFSINO) to make sure if a quota inode is
> > > > valid.
> > > > 
> > > > Solve that problem by initializing the values to NULLFSINO
> > > > if they are 0.
> > > > 
> > > > Note that these values are not written back to on-disk
> > > > superblock unless some quota is enabled on the filesystem.
> > > > 
> > > > Signed-off-by: Chandra Seetharaman <sekharan@xxxxxxxxxx>
> > > > ---
> > > >  fs/xfs/xfs_mount.c |   12 ++++++++++++
> > > >  1 files changed, 12 insertions(+), 0 deletions(-)
> > > > 
> > > > diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> > > > index 2b0ba35..8b95933 100644
> > > > --- a/fs/xfs/xfs_mount.c
> > > > +++ b/fs/xfs/xfs_mount.c
> > > > @@ -572,6 +572,18 @@ out_unwind:
> > > >  static void
> > > >  xfs_sb_quota_from_disk(struct xfs_sb *sbp)
> > > >  {
> > > > +       /*
> > > > +        * older mkfs doesn't initialize quota inodes to NULLFSINO,
> > > > +        * which leads to two values for a quota inode to be invalid:
> > > > +        * 0 and NULLFSINO. Fix it.
> > > > +        */
> > > > +       if (sbp->sb_uquotino == 0)
> > > > +               sbp->sb_uquotino = NULLFSINO;
> > > > +       if (sbp->sb_gquotino == 0)
> > > > +               sbp->sb_gquotino = NULLFSINO;
> > > > +       if (sbp->sb_pquotino == 0)
> > > > +               sbp->sb_pquotino = NULLFSINO;
> > > 
> > > There coment needs to point out that this is changing the in-memory
> > > superblock value right here, so we don't need to make changing
> > > sb_pquotino dependent on the superblock having support for this
> > > feature.
> > 
> > But, we are not just changing just for sb_pquotino, right ?
> 
> Sure, but those other two fields are always present in the
> superblock...
> 
> > Since we are changing all the fields independent of superblock
> > supporting sb_pquotino, I thought the comment should be generic.
> 
> So why is it safe to modify this when sb_pquotino isn't valid in the
> superblock (i.e. v4 superblock) and the only valid on-disk value for
> an unused section of the superblock is zero?
> 
> That's what the comment needs to explain.

How about this:

/*
 * older mkfs doesn't initialize quota inodes to NULLFSINO
 * This leads to in-core values having two different values
 * for a quota inode to be invalid: 0 and NULLFSINO.
 * Change it to a single value NULLFSINO.
 *
 * Note that this change affect only the in-core values. 
 * These values are not written back to disk unless any
 * quota information is written to the disk. Even in that
 * case, sb_pquotino field is not written to disk unless
 * the superblock supports pquotino.
 */

> Cheers,
> 
> Dave.


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