Re: [PATCH 10/11] xfs: fix incorrect remote symlink block count

Ben Myers
2013-05-24T20:39:10Z

On Fri, May 24, 2013 at 03:36:33PM -0500, Ben Myers wrote:
> On Tue, May 21, 2013 at 06:02:09PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > When CRCs are enabled, the number of blocks needed to hold a remote
> > symlink on a 1k block size filesystem may be 2 instead of 1. The
> > transaction reservation for the allocated bloks was not taking this
> blocks
> > into account and only allocating one block. hence when trying to
> H
>
> fixed.
>
> > read or invalidate such symlinks, we are mapping a hole where there
> > should be a block and things go bad at that point.
> >
> > Fix the reservation to use the correct block count, clean up the
> > block count calculation similar to the remote attribute calculation,
> > and add a debug guard to detect when we don't write the entire
> > symlink to disk.
> >
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> > fs/xfs/xfs_symlink.c | 20 ++++++--------------
> > 1 file changed, 6 insertions(+), 14 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
> > index 5f234389..195a403 100644
> > --- a/fs/xfs/xfs_symlink.c
> > +++ b/fs/xfs/xfs_symlink.c
> > @@ -56,16 +56,9 @@ xfs_symlink_blocks(
> > struct xfs_mount *mp,
> > int pathlen)
> > {
> > - int fsblocks = 0;
> > - int len = pathlen;
> > + int buflen = XFS_SYMLINK_BUF_SPACE(mp, mp->m_sb.sb_blocksize);
> >
> > - do {
> > - fsblocks++;
> > - len -= XFS_SYMLINK_BUF_SPACE(mp, mp->m_sb.sb_blocksize);
> > - } while (len > 0);
> > -
> > - ASSERT(fsblocks <= XFS_SYMLINK_MAPS);
> > - return fsblocks;
> > + return (pathlen + buflen - 1) / buflen;
>
> Nice to get rid of that loop.
>
> > }
> >
> > static int
> > @@ -405,7 +398,7 @@ xfs_symlink(
> > if (pathlen <= XFS_LITINO(mp, dp->i_d.di_version))
> > fs_blocks = 0;
> > else
> > - fs_blocks = XFS_B_TO_FSB(mp, pathlen);
> > + fs_blocks = xfs_symlink_blocks(mp, pathlen);
> > resblks = XFS_SYMLINK_SPACE_RES(mp, link_name->len, fs_blocks);
> > error = xfs_trans_reserve(tp, resblks, XFS_SYMLINK_LOG_RES(mp), 0,
> > XFS_TRANS_PERM_LOG_RES, XFS_SYMLINK_LOG_COUNT);
> > @@ -512,7 +505,7 @@ xfs_symlink(
> > cur_chunk = target_path;
> > offset = 0;
> > for (n = 0; n < nmaps; n++) {
> > - char *buf;
> > + char *buf;
> >
> > d = XFS_FSB_TO_DADDR(mp, mval[n].br_startblock);
> > byte_cnt = XFS_FSB_TO_B(mp, mval[n].br_blockcount);
> > @@ -525,9 +518,7 @@ xfs_symlink(
> > bp->b_ops = &xfs_symlink_buf_ops;
> >
> > byte_cnt = XFS_SYMLINK_BUF_SPACE(mp, byte_cnt);
> > - if (pathlen < byte_cnt) {
> > - byte_cnt = pathlen;
> > - }
> > + byte_cnt = min(byte_cnt, pathlen);
>
> The min is necessary due since we can have up to three extents in here,
> according to the comment above the define for XFS_SYMLINK_MAPS. So byte_cnt
> can be less than pathlen.

D'oh. I wanted to point out that it looks like this issue with 'min' here
should be causing problems with symlinks on non-crc enabled filesystems.

-Ben