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xfs: ensure f_ffree returned by statfs() is non-negative 

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.

[ Modified to use max_t as per Christoph's comment. ]

Signed-off-by: Stu Brodsky <sbrodsky@sgi.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
This commit is contained in:
Stuart Brodsky 2010-08-24 11:46:05 +10:00 committed by Dave Chinner
parent efceab1d56
commit 2fe33661fc
1 changed files with 6 additions and 1 deletions
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7
fs/xfs/linux-2.6/xfs_super.c
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@ -1226,6 +1226,7 @@ xfs_fs_statfs(
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 +1250,11 @@ xfs_fs_statfs(
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);
/* make sure statp->f_ffree does not underflow */
ffree = statp->f_files - (sbp->sb_icount - sbp->sb_ifree);
statp->f_ffree = max_t(__int64_t, ffree, 0);
spin_unlock(&mp->m_sb_lock);
if ((ip->i_d.di_flags & XFS_DIFLAG_PROJINHERIT) ||