Re: [PATCH 3/3] xfs: rename buffer cache index variable b_bn

From: Dave Chinner <david@fromorbit.com>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 3/3] xfs: rename buffer cache index variable b_bn
Date: Wed, 18 Aug 2021 09:48:27 +1000	[thread overview]
Message-ID: <20210817234827.GK3657114@dread.disaster.area> (raw)
In-Reply-To: <20210811004632.GA3601443@magnolia>

On Tue, Aug 10, 2021 at 05:46:32PM -0700, Darrick J. Wong wrote:
> On Tue, Aug 10, 2021 at 03:28:51PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > TO stop external users from using b_bn as the disk address of the
> > buffer, rename it to b_index to indicate that it is the buffer cache
> > index, not the block number of the buffer. Code that needs the disk
> > address should use xfs_buf_daddr() to obtain it.
> > 
> > Do the rename and clean up any of the remaining b_bn cruft that is
> > left over and is now unused.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> >  fs/xfs/xfs_buf.c | 19 +++++++++++--------
> >  fs/xfs/xfs_buf.h | 18 +-----------------
> >  2 files changed, 12 insertions(+), 25 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > index c1bb6e41595b..6f6c6937baaa 100644
> > --- a/fs/xfs/xfs_buf.c
> > +++ b/fs/xfs/xfs_buf.c
> > @@ -251,7 +251,7 @@ _xfs_buf_alloc(
> >  		return error;
> >  	}
> >  
> > -	bp->b_bn = map[0].bm_bn;
> > +	bp->b_index = map[0].bm_bn;
> >  	bp->b_length = 0;
> >  	for (i = 0; i < nmaps; i++) {
> >  		bp->b_maps[i].bm_bn = map[i].bm_bn;
> > @@ -459,7 +459,7 @@ _xfs_buf_obj_cmp(
> >  	 */
> >  	BUILD_BUG_ON(offsetof(struct xfs_buf_map, bm_bn) != 0);
> >  
> > -	if (bp->b_bn != map->bm_bn)
> > +	if (bp->b_index != map->bm_bn)
> >  		return 1;
> >  
> >  	if (unlikely(bp->b_length != map->bm_len)) {
> > @@ -481,7 +481,7 @@ static const struct rhashtable_params xfs_buf_hash_params = {
> >  	.min_size		= 32,	/* empty AGs have minimal footprint */
> >  	.nelem_hint		= 16,
> >  	.key_len		= sizeof(xfs_daddr_t),
> > -	.key_offset		= offsetof(struct xfs_buf, b_bn),
> > +	.key_offset		= offsetof(struct xfs_buf, b_index),
> 
> I would've called this field b_rhash_key, since "index" is a kind of
> vague.

Ok.

> > @@ -875,7 +877,7 @@ xfs_buf_read_uncached(
> >  
> >  	/* set up the buffer for a read IO */
> >  	ASSERT(bp->b_map_count == 1);
> > -	bp->b_bn = XFS_BUF_DADDR_NULL;  /* always null for uncached buffers */
> > +	bp->b_index = XFS_BUF_DADDR_NULL;
> >  	bp->b_maps[0].bm_bn = daddr;
> >  	bp->b_flags |= XBF_READ;
> >  	bp->b_ops = ops;
> > @@ -1513,7 +1515,7 @@ _xfs_buf_ioapply(
> >  						   SHUTDOWN_CORRUPT_INCORE);
> >  				return;
> >  			}
> > -		} else if (bp->b_bn != XFS_BUF_DADDR_NULL) {
> > +		} else if (bp->b_index != XFS_BUF_DADDR_NULL) {
> >  			struct xfs_mount *mp = bp->b_mount;
> >  
> >  			/*
> > @@ -1523,7 +1525,8 @@ _xfs_buf_ioapply(
> >  			if (xfs_has_crc(mp)) {
> >  				xfs_warn(mp,
> >  					"%s: no buf ops on daddr 0x%llx len %d",
> > -					__func__, bp->b_bn, bp->b_length);
> > +					__func__, xfs_buf_daddr(bp),
> > +					bp->b_length);
> >  				xfs_hex_dump(bp->b_addr,
> >  						XFS_CORRUPTION_DUMP_LEN);
> >  				dump_stack();
> > @@ -1793,7 +1796,7 @@ xfs_buftarg_drain(
> >  				xfs_buf_alert_ratelimited(bp,
> >  					"XFS: Corruption Alert",
> >  "Corruption Alert: Buffer at daddr 0x%llx had permanent write failures!",
> > -					(long long)bp->b_bn);
> > +					(long long)xfs_buf_daddr(bp));
> 
> These belong in the previous patch, right?

Depends on your POV. This patch cleans up all the internal (mis)uses of
b_bn, while the previous patches addressed all the external uses.
The mods could be in either, I just chose to split internal/external
modification based on the file rather than on the specific (ab)use
being corrected....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com