[PATCH V4] xfs: be honest about used inodes in statfs

[Eric Sandeen]

Because we have lazy counters, it's possible that we over-allocate
inodes past the maxicount (imaxpct) limit.  

A previous commit,

 2fe3366 xfs: ensure f_ffree returned by statfs() is non-negative

stopped statfs from underflowing f_ffree in this case, but that
only happened when we mis-reported f_files, capped at maxicount.

Change statfs to report the actual number of inodes allocated,
even if it is greater than maxicount.  It's reality.
Deal with it.  

Also rework code & rename vars for clarity after input from
dchinner & bfoster.

Signed-off-by: Eric Sandeen <sandeen at redhat.com>
---

V2: code cleanup thanks to Brian
V3: more cleanup thanks to Dave
V4: Oh for crying out loud... (add maxicount test in else)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index f317488..02537f4 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1081,9 +1081,8 @@ xfs_fs_statfs(
 	struct xfs_mount	*mp = XFS_M(dentry->d_sb);
 	xfs_sb_t		*sbp = &mp->m_sb;
 	struct xfs_inode	*ip = XFS_I(dentry->d_inode);
-	__uint64_t		fakeinos, id;
+	__uint64_t		potential, id;
 	xfs_extlen_t		lsize;
-	__int64_t		ffree;
 
 	statp->f_type = XFS_SB_MAGIC;
 	statp->f_namelen = MAXNAMELEN - 1;
@@ -1100,17 +1099,17 @@ xfs_fs_statfs(
 	statp->f_blocks = sbp->sb_dblocks - lsize;
 	statp->f_bfree = statp->f_bavail =
 				sbp->sb_fdblocks - XFS_ALLOC_SET_ASIDE(mp);
-	fakeinos = statp->f_bfree << sbp->sb_inopblog;
-	statp->f_files =
-	    MIN(sbp->sb_icount + fakeinos, (__uint64_t)XFS_MAXINUMBER);
-	if (mp->m_maxicount)
-		statp->f_files = min_t(typeof(statp->f_files),
-					statp->f_files,
-					mp->m_maxicount);
-
-	/* 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);
+
+	/* Potential new inodes in free blocks, limited by maxicount */
+	potential = statp->f_bfree << sbp->sb_inopblog;
+	if (mp->m_maxicount > sbp->sb_icount)
+		potential = min(mp->m_maxicount - sbp->sb_icount, potential);
+	else if (mp->m_maxicount)
+		potential = 0;
+
+	/* Total possible files is current inodes + potential new inodes */
+	statp->f_files = min_t(u64, sbp->sb_icount + potential, XFS_MAXINUMBER);
+	statp->f_ffree = statp->f_files - (sbp->sb_icount - sbp->sb_ifree);
 
 	spin_unlock(&mp->m_sb_lock);