Re: [PATCH 12/13] xfs: create a new buf_ops pointer to verify structure metadata

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 12/13] xfs: create a new buf_ops pointer to verify structure metadata
Date: Tue, 19 Dec 2017 10:15:29 -0800	[thread overview]
Message-ID: <20171219181529.GB11969@magnolia> (raw)
In-Reply-To: <20171219062205.GV4094@dastard>

On Tue, Dec 19, 2017 at 05:22:05PM +1100, Dave Chinner wrote:
> On Wed, Dec 13, 2017 at 03:59:25PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Expose all metadata structure buffer verifier functions via buf_ops.
> > These will be used by the online scrub mechanism to look for problems
> > with buffers that are already sitting around in memory.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> ....
> > @@ -2468,7 +2478,7 @@ xfs_agf_read_verify(
> >  	.verify_write = xfs_attr3_leaf_write_verify,
> > +	.verify_struct = xfs_attr3_leaf_verify,
> >  };
> >  
> >  int
> > diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
> > index d4d2902..1be995b 100644
> > --- a/fs/xfs/libxfs/xfs_attr_remote.c
> > +++ b/fs/xfs/libxfs/xfs_attr_remote.c
> > @@ -204,10 +204,42 @@ xfs_attr3_rmt_write_verify(
> >  	ASSERT(len == 0);
> >  }
> >  
> > +static xfs_failaddr_t
> > +xfs_attr3_rmt_verify_struct(
> > +	struct xfs_buf	*bp)
> > +{
> > +	struct xfs_mount *mp = bp->b_target->bt_mount;
> > +	char		*ptr;
> > +	void		*failed_at;
> > +	int		len;
> > +	xfs_daddr_t	bno;
> > +	int		blksize = mp->m_attr_geo->blksize;
> > +
> > +	/* no verification of non-crc buffers */
> > +	if (!xfs_sb_version_hascrc(&mp->m_sb))
> > +		return NULL;
> > +
> > +	ptr = bp->b_addr;
> > +	bno = bp->b_bn;
> > +	len = BBTOB(bp->b_length);
> > +	ASSERT(len >= blksize);
> > +
> > +	while (len > 0) {
> > +		if ((failed_at = xfs_attr3_rmt_verify(mp, ptr, blksize, bno)))
> > +			return failed_at;
> > +		len -= blksize;
> > +		ptr += blksize;
> > +		bno += BTOBB(blksize);
> > +	}
> > +
> > +	return NULL;
> > +}
> 
> I'd much prefer to see this combined with
> xfs_attr3_rmt_read_verify() rather than having another copy of this
> iteration code. They really only vary by whether the CRC is checked
> in the loop....
> 
> ....
> 
> > +static xfs_failaddr_t
> > +xfs_dquot_buf_verify_struct(
> > +	struct xfs_buf	*bp)
> > +{
> > +	struct xfs_mount	*mp = bp->b_target->bt_mount;
> > +
> > +	if (!xfs_dquot_buf_verify(mp, bp, 0))
> > +		return __this_address;
> > +	return NULL;
> > +}
> 
> I can't remember what happened exactly with dquot buffers earlire in
> the patchset, but why isn't it returning a failaddr like all the
> other structure verifiers?

The dquot verifiers are sufficiently different from everything else
(verbose error reporting, some ability to zap garbage data) that I was
going to send that as a separate cleanup series.

I /think/ the solution is to disentangle xfs_dqcheck into a separate
check routine that returns xfs_failaddr_t like everything else (at a
cost of the removal of all the xfs_alert calls) so that the error
reports become "xfs: quota buffer XXX error at xfs_dqcheck+0x74" like
everything else.  The caller becomes directly responsible for printing a
warning message (instead of XFS_QMOPT_DOWARN).

Then, the quota repair piece becomes a separate function which the
XFS_QMOPT_DQREPAIR callers can call directly.

Sound good?

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> --
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