[PATCH] VFS: Permit filesystem to perform statfs with a known root dentry

Give the statfs superblock operation a dentry pointer rather than a superblock
pointer.

This complements the get_sb() patch.  That reduced the significance of
sb->s_root, allowing NFS to place a fake root there.  However, NFS does
require a dentry to use as a target for the statfs operation.  This permits
the root in the vfsmount to be used instead.

linux/mount.h has been added where necessary to make allyesconfig build
successfully.

Interest has also been expressed for use with the FUSE and XFS filesystems.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Nathan Scott <nathans@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/jfs/super.c

@@ -139,9 +139,9 @@ static void jfs_destroy_inode(struct inode *inode)
 	kmem_cache_free(jfs_inode_cachep, ji);
 }
 
-static int jfs_statfs(struct super_block *sb, struct kstatfs *buf)
+static int jfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
-	struct jfs_sb_info *sbi = JFS_SBI(sb);
+	struct jfs_sb_info *sbi = JFS_SBI(dentry->d_sb);
 	s64 maxinodes;
 	struct inomap *imap = JFS_IP(sbi->ipimap)->i_imap;