[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/freevxfs/vxfs_super.c

@@ -40,6 +40,7 @@
 #include <linux/slab.h>
 #include <linux/stat.h>
 #include <linux/vfs.h>
+#include <linux/mount.h>
 
 #include "vxfs.h"
 #include "vxfs_extern.h"
@@ -55,7 +56,7 @@ MODULE_ALIAS("vxfs"); /* makes mount -t vxfs autoload the module */
 
 
 static void		vxfs_put_super(struct super_block *);
-static int		vxfs_statfs(struct super_block *, struct kstatfs *);
+static int		vxfs_statfs(struct dentry *, struct kstatfs *);
 static int		vxfs_remount(struct super_block *, int *, char *);
 
 static struct super_operations vxfs_super_ops = {
@@ -90,12 +91,12 @@ vxfs_put_super(struct super_block *sbp)
 
 /**
  * vxfs_statfs - get filesystem information
- * @sbp:	VFS superblock
+ * @dentry:	VFS dentry to locate superblock
  * @bufp:	output buffer
  *
  * Description:
  *   vxfs_statfs fills the statfs buffer @bufp with information
- *   about the filesystem described by @sbp.
+ *   about the filesystem described by @dentry.
  *
  * Returns:
  *   Zero.
@@ -107,12 +108,12 @@ vxfs_put_super(struct super_block *sbp)
  *   This is everything but complete...
  */
 static int
-vxfs_statfs(struct super_block *sbp, struct kstatfs *bufp)
+vxfs_statfs(struct dentry *dentry, struct kstatfs *bufp)
 {
-	struct vxfs_sb_info		*infp = VXFS_SBI(sbp);
+	struct vxfs_sb_info		*infp = VXFS_SBI(dentry->d_sb);
 
 	bufp->f_type = VXFS_SUPER_MAGIC;
-	bufp->f_bsize = sbp->s_blocksize;
+	bufp->f_bsize = dentry->d_sb->s_blocksize;
 	bufp->f_blocks = infp->vsi_raw->vs_dsize;
 	bufp->f_bfree = infp->vsi_raw->vs_free;
 	bufp->f_bavail = 0;