[3.16.y-ckt stable] Patch "ext4: fix accidental flag aliasing in ext4_map_blocks flags" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ext4: fix accidental flag aliasing in ext4_map_blocks flags

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 8d41197b4c9a26cba20b2346ec5e1875fe85e4c9 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso at mit.edu>
Date: Mon, 1 Sep 2014 14:33:09 -0400
Subject: ext4: fix accidental flag aliasing in ext4_map_blocks flags

commit bd30d702fc320085f178d22866b32fdc4736c991 upstream.

Commit b8a8684502a0f introduced an accidental flag aliasing between
EXT4_EX_NOCACHE and EXT4_GET_BLOCKS_CONVERT_UNWRITTEN.

Fortunately, this didn't introduce any untorward side effects --- we
got lucky.  Nevertheless, fix this and leave a warning to hopefully
avoid this from happening in the future.

Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/ext4/ext4.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 20889da7f8a0..e00dc9772402 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -569,6 +569,7 @@ enum {
 #define EXT4_GET_BLOCKS_NO_PUT_HOLE		0x0200
 	/* Convert written extents to unwritten */
 #define EXT4_GET_BLOCKS_CONVERT_UNWRITTEN	0x0400
+/* DO NOT ASSIGN ADDITIONAL FLAG VALUES WITHOUT ADJUSTING THE FLAGS BELOW */

 /*
  * The bit position of these flags must not overlap with any of the
@@ -579,8 +580,8 @@ enum {
  * caching the extents when reading from the extent tree while a
  * truncate or punch hole operation is in progress.
  */
-#define EXT4_EX_NOCACHE				0x0400
-#define EXT4_EX_FORCE_CACHE			0x0800
+#define EXT4_EX_NOCACHE				0x0800
+#define EXT4_EX_FORCE_CACHE			0x1000

 /*
  * Flags used by ext4_free_blocks