[PATCH] reiserfs: fix is_reusable bitmap check to not traverse the bitmap info array

There is a check in is_reusable to determine if a particular block is a bitmap
block.  It verifies this by going through the array of bitmap block buffer
heads and comparing the block number to each one.

Bitmap blocks are at defined locations on the disk in both old and current
formats.  Simply checking against the known good values is enough.

This is a trivial optimization for a non-production codepath, but this is the
first in a series of patches that will ultimately remove the buffer heads from
that array.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Cc: <reiserfs-dev@namesys.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/reiserfs/bitmap.c

@@ -50,16 +50,15 @@ static inline void get_bit_address(struct super_block *s,
 {
 	/* It is in the bitmap block number equal to the block
 	 * number divided by the number of bits in a block. */
-	*bmap_nr = block / (s->s_blocksize << 3);
+	*bmap_nr = block >> (s->s_blocksize_bits + 3);
 	/* Within that bitmap block it is located at bit offset *offset. */
 	*offset = block & ((s->s_blocksize << 3) - 1);
-	return;
 }
 
 #ifdef CONFIG_REISERFS_CHECK
 int is_reusable(struct super_block *s, b_blocknr_t block, int bit_value)
 {
-	int i, j;
+	int bmap, offset;
 
 	if (block == 0 || block >= SB_BLOCK_COUNT(s)) {
 		reiserfs_warning(s,
@@ -68,34 +67,45 @@ int is_reusable(struct super_block *s, b_blocknr_t block, int bit_value)
 		return 0;
 	}
 
-	/* it can't be one of the bitmap blocks */
-	for (i = 0; i < SB_BMAP_NR(s); i++)
-		if (block == SB_AP_BITMAP(s)[i].bh->b_blocknr) {
+	get_bit_address(s, block, &bmap, &offset);
+
+	/* Old format filesystem? Unlikely, but the bitmaps are all up front so
+	 * we need to account for it. */
+	if (unlikely(test_bit(REISERFS_OLD_FORMAT,
+			      &(REISERFS_SB(s)->s_properties)))) {
+		b_blocknr_t bmap1 = REISERFS_SB(s)->s_sbh->b_blocknr + 1;
+		if (block >= bmap1 && block <= bmap1 + SB_BMAP_NR(s)) {
+			reiserfs_warning(s, "vs: 4019: is_reusable: "
+					 "bitmap block %lu(%u) can't be freed or reused",
+					 block, SB_BMAP_NR(s));
+			return 0;
+		}
+	} else {
+		if (offset == 0) {
 			reiserfs_warning(s, "vs: 4020: is_reusable: "
 					 "bitmap block %lu(%u) can't be freed or reused",
 					 block, SB_BMAP_NR(s));
 			return 0;
 		}
+	}
 
-	get_bit_address(s, block, &i, &j);
-
-	if (i >= SB_BMAP_NR(s)) {
+	if (bmap >= SB_BMAP_NR(s)) {
 		reiserfs_warning(s,
 				 "vs-4030: is_reusable: there is no so many bitmap blocks: "
-				 "block=%lu, bitmap_nr=%d", block, i);
+				 "block=%lu, bitmap_nr=%d", block, bmap);
 		return 0;
 	}
 
 	if ((bit_value == 0 &&
-	     reiserfs_test_le_bit(j, SB_AP_BITMAP(s)[i].bh->b_data)) ||
+	     reiserfs_test_le_bit(offset, SB_AP_BITMAP(s)[bmap].bh->b_data)) ||
 	    (bit_value == 1 &&
-	     reiserfs_test_le_bit(j, SB_AP_BITMAP(s)[i].bh->b_data) == 0)) {
+	     reiserfs_test_le_bit(offset, SB_AP_BITMAP(s)[bmap].bh->b_data) == 0)) {
 		reiserfs_warning(s,
 				 "vs-4040: is_reusable: corresponding bit of block %lu does not "
-				 "match required value (i==%d, j==%d) test_bit==%d",
-				 block, i, j, reiserfs_test_le_bit(j,
+				 "match required value (bmap==%d, offset==%d) test_bit==%d",
+				 block, bmap, offset, reiserfs_test_le_bit(offset,
 								   SB_AP_BITMAP
-								   (s)[i].bh->
+								   (s)[bmap].bh->
 								   b_data));
 
 		return 0;

fs/reiserfs/super.c

@@ -1818,6 +1818,8 @@ static int reiserfs_fill_super(struct super_block *s, void *data, int silent)
 	if (is_reiserfs_3_5(rs)
 	    || (is_reiserfs_jr(rs) && SB_VERSION(s) == REISERFS_VERSION_1))
 		set_bit(REISERFS_3_5, &(sbi->s_properties));
+	else if (old_format)
+		set_bit(REISERFS_OLD_FORMAT, &(sbi->s_properties));
 	else
 		set_bit(REISERFS_3_6, &(sbi->s_properties));
 

include/linux/reiserfs_fs_sb.h

@@ -414,6 +414,7 @@ struct reiserfs_sb_info {
 /* Definitions of reiserfs on-disk properties: */
 #define REISERFS_3_5 0
 #define REISERFS_3_6 1
+#define REISERFS_OLD_FORMAT 2
 
 enum reiserfs_mount_options {
 /* Mount options */