[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/isofs/inode.c

@@ -56,7 +56,7 @@ static void isofs_put_super(struct super_block *sb)
 }
 
 static void isofs_read_inode(struct inode *);
-static int isofs_statfs (struct super_block *, struct kstatfs *);
+static int isofs_statfs (struct dentry *, struct kstatfs *);
 
 static kmem_cache_t *isofs_inode_cachep;
 
@@ -901,8 +901,10 @@ out_freesbi:
 	return -EINVAL;
 }
 
-static int isofs_statfs (struct super_block *sb, struct kstatfs *buf)
+static int isofs_statfs (struct dentry *dentry, struct kstatfs *buf)
 {
+	struct super_block *sb = dentry->d_sb;
+
 	buf->f_type = ISOFS_SUPER_MAGIC;
 	buf->f_bsize = sb->s_blocksize;
 	buf->f_blocks = (ISOFS_SB(sb)->s_nzones