fat (exportfs): rebuild directory-inode if fat_dget()

This patch enables rebuilding of directory inodes which are not present in
the cache.This is done by traversing the disk clusters to find the
directory entry of the parent directory and using its i_pos to build the
inode.

The traversal is done by fat_scan_logstart() which is similar to
fat_scan() but matches i_pos values instead of names.fat_scan_logstart()
needs an inode parameter to work, for which a dummy inode is created by
it's caller fat_rebuild_parent().  This dummy inode is destroyed after the
traversal completes.

All this is done  only if the nostale_ro nfs mount option is specified.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ravishankar N <ravi.n1@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.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, 23 insertions, 0 deletions

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 165012ef363a..7a6f02caf286 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -964,6 +964,29 @@ int fat_scan(struct inode *dir, const unsigned char *name,
 }
 EXPORT_SYMBOL_GPL(fat_scan);
 
+/*
+ * Scans a directory for a given logstart.
+ * Returns an error code or zero.
+ */
+int fat_scan_logstart(struct inode *dir, int i_logstart,
+		      struct fat_slot_info *sinfo)
+{
+	struct super_block *sb = dir->i_sb;
+
+	sinfo->slot_off = 0;
+	sinfo->bh = NULL;
+	while (fat_get_short_entry(dir, &sinfo->slot_off, &sinfo->bh,
+				   &sinfo->de) >= 0) {
+		if (fat_get_start(MSDOS_SB(sb), sinfo->de) == i_logstart) {
+			sinfo->slot_off -= sizeof(*sinfo->de);
+			sinfo->nr_slots = 1;
+			sinfo->i_pos = fat_make_i_pos(sb, sinfo->bh, sinfo->de);
+			return 0;
+		}
+	}
+	return -ENOENT;
+}
+
 static int __fat_remove_entries(struct inode *dir, loff_t pos, int nr_slots)
 {
 	struct super_block *sb = dir->i_sb;