fat (exportfs): fix dentry reconnection

Maintain an index of directory inodes by starting cluster, so that
fat_get_parent() can return the proper cached inode rather than inventing
one that cannot be traced back to the filesystem root.

Add a new msdos/vfat binary mount option "nfs" so that FAT filesystems
that are _not_ exported via NFS are not saddled with maintenance of an
index they will never use.

Finally, simplify NFS file handle generation and lookups.  An
ext2-congruent implementation is adequate for FAT needs.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 9 deletions

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index d70d8f31f704..55e088cc0613 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -872,21 +872,23 @@ static int fat_get_short_entry(struct inode *dir, loff_t *pos,
 }
 
 /*
- * The ".." entry can not provide the "struct fat_slot_info" informations
- * for inode. So, this function provide the some informations only.
+ * The ".." entry can not provide the "struct fat_slot_info" information
+ * for inode, nor a usable i_pos. So, this function provides some information
+ * only.
+ *
+ * Since this function walks through the on-disk inodes within a directory,
+ * callers are responsible for taking any locks necessary to prevent the
+ * directory from changing.
  */
 int fat_get_dotdot_entry(struct inode *dir, struct buffer_head **bh,
-                         struct msdos_dir_entry **de, loff_t *i_pos)
+                         struct msdos_dir_entry **de)
 {
-        loff_t offset;
+        loff_t offset = 0;
 
-        offset = 0;
-        *bh = NULL;
+        *de = NULL;
         while (fat_get_short_entry(dir, &offset, bh, de) >= 0) {
-                if (!strncmp((*de)->name, MSDOS_DOTDOT, MSDOS_NAME)) {
-                        *i_pos = fat_make_i_pos(dir->i_sb, *bh, *de);
+                if (!strncmp((*de)->name, MSDOS_DOTDOT, MSDOS_NAME))
                         return 0;
-                }
         }
         return -ENOENT;
 }