[PATCH v3] xfs: ensure f_ffree returned by statfs() is non-negative

[Stuart Brodsky]

Because of delayed updates to sb_icount field in the super block, it
is possible to allocate over maxicount number of inodes.  This
causes the arithmetic to calculate a negative number of free inodes
in user commands like df or stat -f.

Since maxicount is a somewhat arbitrary number, a slight over
allocation is not critical but user commands should be displayed as
0 or greater and never go negative.  To do this the value in the
stats buffer f_ffree is capped to never go negative.

Signed-off-by: Stu Brodsky <sbrodsky at sgi.com>

--- a/fs/xfs/linux-2.6/xfs_super.c.orig 2010-07-20
06:06:19.269572013-0500
+++ b/fs/xfs/linux-2.6/xfs_super.c 2010-07-20 08:09:17.773570840 -0500
@@ -1226,6 +1226,7 @@
        struct xfs_inode        *ip = XFS_I(dentry->d_inode);
        __uint64_t              fakeinos, id;
        xfs_extlen_t            lsize;
+       __int64_t               ffree;
  
        statp->f_type = XFS_SB_MAGIC;
        statp->f_namelen = MAXNAMELEN - 1;
@@ -1249,7 +1250,9 @@
        statp->f_files = min_t(typeof(statp->f_files),
                                        statp->f_files,
                                        mp->m_maxicount);
-       statp->f_ffree = statp->f_files - (sbp->sb_icount -
sbp->sb_ifree);
+       ffree = statp->f_files - (sbp->sb_icount - sbp->sb_ifree);
+       statp->f_ffree = (__u64) (ffree < 0 ? 0 : ffree);
+
        spin_unlock(&mp->m_sb_lock);

        if ((ip->i_d.di_flags & XFS_DIFLAG_PROJINHERIT) ||
-- 
Stuart Brodsky
2750 Blue Water Road
Eagan, MN. 55121
651-683-7910
<sbrodsky at sgi.com>