Re: [PATCH 28/37] xfs_db: avoid libxfs buffer lookup warnings

Dave Chinner
2013-11-06T02:20:23Z

Looks like I messed up the patch subject. It should be:

"xfs_db: use inode cluster buffers for inode IO"

On Wed, Nov 06, 2013 at 12:07:14PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> When we mount the filesystem inside xfs_db, libxfs is tasked with
> reading some information from disk, such as root inodes. Because
> libxfs does this inode reading, it uses inode cluster buffers to
> read the inodes. xfs_db, OTOH, just uses FSB sized buffers to read
> inodes, and hence xfs_db throws a warning when reading the root
> inode block like so:
>
> $ sudo xfs_db -c "sb 0" -c "p rootino" -c "inode 32" /dev/vda
> Version 5 superblock detected. xfsprogs has EXPERIMENTAL support enabled!
> Use of these features is at your own risk!
> rootino = 32
> 7f59f20e6740: Badness in key lookup (length)
> bp=(bno 0x20, len 8192 bytes) key=(bno 0x20, len 1024 bytes)
> $
>
> There is another way this can happen, and that is dumping raw data
> from disk using either the "fsb NNN" or "daddr MMM" commands to dump
> untyped information. This is always read in sector or filesystem
> block units, and so will cause similar badness warnings.
>
> To avoid this problem when reading inodes, teach xfs_db to read
> inode clusters rather individual filesystem blocks when asked to
> read an inode.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> db/inode.c | 33 +++++++++++++++++++++++++++++++--
> 1 file changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/db/inode.c b/db/inode.c
> index 4090855..24170ba 100644
> --- a/db/inode.c
> +++ b/db/inode.c
> @@ -623,6 +623,14 @@ inode_u_symlink_count(
> (int)be64_to_cpu(dip->di_size) : 0;
> }
>
> +/*
> + * We are now using libxfs for our IO backend, so we should always try to use
> + * inode cluster buffers rather than filesystem block sized buffers for reading
> + * inodes. This means that we always use the same buffers as libxfs operations
> + * does, and that avoids buffer cache issues caused by overlapping buffers. This
> + * can be seen clearly when trying to read the root inode. Much of this logic is
> + * similar to libxfs_imap().
> + */
> void
> set_cur_inode(
> xfs_ino_t ino)
> @@ -632,6 +640,9 @@ set_cur_inode(
> xfs_agnumber_t agno;
> xfs_dinode_t *dip;
> int offset;
> + int numblks = blkbb;
> + xfs_agblock_t cluster_agbno;
> +
>
> agno = XFS_INO_TO_AGNO(mp, ino);
> agino = XFS_INO_TO_AGINO(mp, ino);
> @@ -644,6 +655,24 @@ set_cur_inode(
> return;
> }
> cur_agno = agno;
> +
> + if (mp->m_inode_cluster_size > mp->m_sb.sb_blocksize &&
> + mp->m_inoalign_mask) {
> + xfs_agblock_t chunk_agbno;
> + xfs_agblock_t offset_agbno;
> + int blks_per_cluster;
> +
> + blks_per_cluster = mp->m_inode_cluster_size >>
> + mp->m_sb.sb_blocklog;
> + offset_agbno = agbno & mp->m_inoalign_mask;
> + chunk_agbno = agbno - offset_agbno;
> + cluster_agbno = chunk_agbno +
> + ((offset_agbno / blks_per_cluster) * blks_per_cluster);
> + offset += ((agbno - cluster_agbno) * mp->m_sb.sb_inopblock);
> + numblks = XFS_FSB_TO_BB(mp, blks_per_cluster);
> + } else
> + cluster_agbno = agbno;
> +
> /*
> * First set_cur to the block with the inode
> * then use off_cur to get the right part of the buffer.
> @@ -651,8 +680,8 @@ set_cur_inode(
> ASSERT(typtab[TYP_INODE].typnm == TYP_INODE);
>
> /* ingore ring update here, do it explicitly below */
> - set_cur(&typtab[TYP_INODE], XFS_AGB_TO_DADDR(mp, agno, agbno),
> - blkbb, DB_RING_IGN, NULL);
> + set_cur(&typtab[TYP_INODE], XFS_AGB_TO_DADDR(mp, agno, cluster_agbno),
> + numblks, DB_RING_IGN, NULL);
> off_cur(offset << mp->m_sb.sb_inodelog, mp->m_sb.sb_inodesize);
> dip = iocur_top->data;
> iocur_top->ino_crc_ok = libxfs_dinode_verify(mp, ino, dip);
> --
> 1.8.4.rc3
>
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--
Dave Chinner
david@fromorbit.com