ext4: Return unwritten buffer head when trying to read from prealloc space.

ext4_ext_get_blocks() returns the number of blocks allocated with buffer
head unmapped for a read from prealloc space.  This is needed so that
delayed allocation doesn't do block reservation for prealloc space
since the blocks are already reserved on disk.  Mark the buffer head
unwritten.  Some code paths try to read the block if the buffer_head is
not new and no uptodate.  Marking the buffer head unwritten avoids this
reading.

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, 2 insertions, 0 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index f4ef0b745a53..7733e2943367 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2580,6 +2580,8 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
                                  */
                                 if (allocated > max_blocks)
                                         allocated = max_blocks;
+                                /* mark the buffer unwritten */
+                                __set_bit(BH_Unwritten, &bh_result->b_state);
                                 goto out2;
                         }