[PATCH] BLOCK: Remove dependence on existence of blockdev_superblock [try #6]

Move blockdev_superblock extern declaration from fs/fs-writeback.c to a
headerfile and remove the dependence on it by wrapping it in a macro.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/fs-writeback.c

@@ -319,7 +319,7 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
 
 		if (!bdi_cap_writeback_dirty(bdi)) {
 			list_move(&inode->i_list, &sb->s_dirty);
-			if (sb == blockdev_superblock) {
+			if (sb_is_blkdev_sb(sb)) {
 				/*
 				 * Dirty memory-backed blockdev: the ramdisk
 				 * driver does this.  Skip just this inode
@@ -336,14 +336,14 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
 
 		if (wbc->nonblocking && bdi_write_congested(bdi)) {
 			wbc->encountered_congestion = 1;
-			if (sb != blockdev_superblock)
+			if (!sb_is_blkdev_sb(sb))
 				break;		/* Skip a congested fs */
 			list_move(&inode->i_list, &sb->s_dirty);
 			continue;		/* Skip a congested blockdev */
 		}
 
 		if (wbc->bdi && bdi != wbc->bdi) {
-			if (sb != blockdev_superblock)
+			if (!sb_is_blkdev_sb(sb))
 				break;		/* fs has the wrong queue */
 			list_move(&inode->i_list, &sb->s_dirty);
 			continue;		/* blockdev has wrong queue */

fs/internal.h

@@ -17,6 +17,8 @@
 extern struct super_block *blockdev_superblock;
 extern void __init bdev_cache_init(void);
 
+#define sb_is_blkdev_sb(sb) ((sb) == blockdev_superblock)
+
 /*
  * char_dev.c
  */