ext4: Use a fake block number for delayed new buffer_head

Use a very large unsigned number (~0xffff) as as the fake block number
for the delayed new buffer. The VFS should never try to write out this
number, but if it does, this will make it obvious.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d4b634ae06bd..0ac31a06422b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2297,6 +2297,10 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                                   struct buffer_head *bh_result, int create)
 {
         int ret = 0;
+        sector_t invalid_block = ~((sector_t) 0xffff);
+
+        if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
+                invalid_block = ~0;
 
         BUG_ON(create == 0);
         BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
@@ -2318,7 +2322,7 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                         /* not enough space to reserve */
                         return ret;
 
-                map_bh(bh_result, inode->i_sb, 0);
+                map_bh(bh_result, inode->i_sb, invalid_block);
                 set_buffer_new(bh_result);
                 set_buffer_delay(bh_result);
         } else if (ret > 0) {