Do not update the fsinfo block on each update of any fat block, this

is excessive. Postpone the flush of the fsinfo to VFS_SYNC(),
remembering the need for update with the flag MSDOSFS_FSIMOD, stored
in pm_flags.

FAT32 specification describes both FSI_Free_Count and FSI_Nxt_Free as
the advisory hints, not requiring them to be correct.

Based on the patch from bde, modified by me.

Reviewed by: bde
MFC after:   2 weeks

3 files changed, 45 insertions, 30 deletions

diff --git a/sys/fs/msdosfs/msdosfs_fat.c b/sys/fs/msdosfs/msdosfs_fat.c
index 3994042..c660601 100644
--- a/sys/fs/msdosfs/msdosfs_fat.c
+++ b/sys/fs/msdosfs/msdosfs_fat.c
@@ -328,29 +328,6 @@ updatefats(pmp, bp, fatbn)
 	printf("updatefats(pmp %p, bp %p, fatbn %lu)\n", pmp, bp, fatbn);
 #endif
 
-	/*
-	 * If we have an FSInfo block, update it.
-	 */
-	if (pmp->pm_fsinfo) {
-		if (bread(pmp->pm_devvp, pmp->pm_fsinfo, pmp->pm_BytesPerSec,
-		    NOCRED, &bpn) != 0) {
-			/*
-			 * Ignore the error, but turn off FSInfo update for the future.
-			 */
-			pmp->pm_fsinfo = 0;
-			brelse(bpn);
-		} else {
-			struct fsinfo *fp = (struct fsinfo *)bpn->b_data;
-
-			putulong(fp->fsinfree, pmp->pm_freeclustercount);
-			putulong(fp->fsinxtfree, pmp->pm_nxtfree);
-			if (pmp->pm_flags & MSDOSFSMNT_WAITONFAT)
-				bwrite(bpn);
-			else
-				bdwrite(bpn);
-		}
-	}
-
 	if (pmp->pm_flags & MSDOSFS_FATMIRROR) {
 		/*
 		 * Now copy the block(s) of the modified fat to the other copies of
@@ -393,9 +370,6 @@ updatefats(pmp, bp, fatbn)
 		bwrite(bp);
 	else
 		bdwrite(bp);
-	/*
-	 * Maybe update fsinfo sector here?
-	 */
 }
 
 /*
@@ -431,6 +405,7 @@ usemap_alloc(pmp, cn)
 	pmp->pm_inusemap[cn / N_INUSEBITS] |= 1 << (cn % N_INUSEBITS);
 	KASSERT(pmp->pm_freeclustercount > 0, ("usemap_alloc: too little"));
 	pmp->pm_freeclustercount--;
+	pmp->pm_flags |= MSDOSFS_FSIMOD;
 }
 
 static __inline void
@@ -441,6 +416,7 @@ usemap_free(pmp, cn)
 
 	MSDOSFS_ASSERT_MP_LOCKED(pmp);
 	pmp->pm_freeclustercount++;
+	pmp->pm_flags |= MSDOSFS_FSIMOD;
 	KASSERT((pmp->pm_inusemap[cn / N_INUSEBITS] & (1 << (cn % N_INUSEBITS)))
 	    != 0, ("Freeing unused sector %ld %ld %x", cn, cn % N_INUSEBITS,
 		(unsigned)pmp->pm_inusemap[cn / N_INUSEBITS]));
@@ -742,7 +718,10 @@ chainalloc(pmp, start, count, fillwith, retcluster, got)
 
 	for (cl = start, n = count; n-- > 0;)
 		usemap_alloc(pmp, cl++);
-
+	pmp->pm_nxtfree = start + count;
+	if (pmp->pm_nxtfree > pmp->pm_maxcluster)
+		pmp->pm_nxtfree = CLUST_FIRST;
+	pmp->pm_flags |= MSDOSFS_FSIMOD;
 	error = fatchain(pmp, start, count, fillwith);
 	if (error != 0)
 		return (error);
@@ -754,9 +733,6 @@ chainalloc(pmp, start, count, fillwith, retcluster, got)
 		*retcluster = start;
 	if (got)
 		*got = count;
-	pmp->pm_nxtfree = start + count;
-	if (pmp->pm_nxtfree > pmp->pm_maxcluster)
-		pmp->pm_nxtfree = CLUST_FIRST;
 	return (0);
 }
 
diff --git a/sys/fs/msdosfs/msdosfs_vfsops.c b/sys/fs/msdosfs/msdosfs_vfsops.c
index a209970..213dd00 100644
--- a/sys/fs/msdosfs/msdosfs_vfsops.c
+++ b/sys/fs/msdosfs/msdosfs_vfsops.c
@@ -896,6 +896,40 @@ msdosfs_statfs(struct mount *mp, struct statfs *sbp)
 	return (0);
 }
 
+/*
+ * If we have an FSInfo block, update it.
+ */
+static int
+msdosfs_fsiflush(struct msdosfsmount *pmp, int waitfor)
+{
+	struct fsinfo *fp;
+	struct buf *bp;
+	int error;
+
+	MSDOSFS_LOCK_MP(pmp);
+	if (pmp->pm_fsinfo == 0 || (pmp->pm_flags & MSDOSFS_FSIMOD) == 0) {
+		error = 0;
+		goto unlock;
+	}
+	error = bread(pmp->pm_devvp, pmp->pm_fsinfo, pmp->pm_BytesPerSec,
+	    NOCRED, &bp);
+	if (error != 0) {
+		brelse(bp);
+		goto unlock;
+	}
+	fp = (struct fsinfo *)bp->b_data;
+	putulong(fp->fsinfree, pmp->pm_freeclustercount);
+	putulong(fp->fsinxtfree, pmp->pm_nxtfree);
+	pmp->pm_flags &= ~MSDOSFS_FSIMOD;
+	if (waitfor == MNT_WAIT)
+		error = bwrite(bp);
+	else
+		bawrite(bp);
+unlock:
+	MSDOSFS_UNLOCK_MP(pmp);
+	return (error);
+}
+
 static int
 msdosfs_sync(struct mount *mp, int waitfor)
 {
@@ -958,6 +992,10 @@ loop:
 			allerror = error;
 		VOP_UNLOCK(pmp->pm_devvp, 0);
 	}
+
+	error = msdosfs_fsiflush(pmp, waitfor);
+	if (error != 0)
+		allerror = error;
 	return (allerror);
 }
 
diff --git a/sys/fs/msdosfs/msdosfsmount.h b/sys/fs/msdosfs/msdosfsmount.h
index 673095e..10ed95b 100644
--- a/sys/fs/msdosfs/msdosfsmount.h
+++ b/sys/fs/msdosfs/msdosfsmount.h
@@ -262,6 +262,7 @@ struct msdosfs_args {
 #define	MSDOSFSMNT_WAITONFAT	0x40000000	/* mounted synchronous	*/
 #define	MSDOSFS_FATMIRROR	0x20000000	/* FAT is mirrored */
 #define	MSDOSFS_LARGEFS		0x10000000	/* perform fileno mapping */
+#define	MSDOSFS_FSIMOD		0x01000000
 
 #define MSDOSFS_ARGSMAGIC	0xe4eff300