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

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 10/11] xfs: fix incorrect remote symlink block count
From: Ben Myers <bpm@xxxxxxx>
Date: Fri, 24 May 2013 15:36:33 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1369123330-9579-11-git-send-email-david@xxxxxxxxxxxxx>
References: <1369123330-9579-1-git-send-email-david@xxxxxxxxxxxxx> <1369123330-9579-11-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Tue, May 21, 2013 at 06:02:09PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> ---
>  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.

Looks good.

Reviewed-by: Ben Myers <bpm@xxxxxxx>

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