[PATCH 3/4] UAPI: Fix endianness conditionals in linux/raid/md_p.h

[David Howells]

In the UAPI header files, __BIG_ENDIAN and __LITTLE_ENDIAN must be compared
against __BYTE_ORDER in preprocessor conditionals where these are exposed to
userspace (that is they're not inside __KERNEL__ conditionals).

However, in the main kernel the norm is to check for "defined(__XXX_ENDIAN)"
rather than comparing against __BYTE_ORDER and this has incorrectly leaked
into the userspace headers.

The definition of struct mdp_superblock_s in linux/raid/md_p.h is wrong in this
way.  Note that userspace will likely interpret the ordering of the fields
incorrectly as the big-endian variant on a little-endian machines - depending
on header inclusion order.

[!!!] NOTE [!!!]  This patch may adversely change the userspace API.  It might
be better to fix the ordering of events_hi, events_lo, cp_events_hi and
cp_events_lo in struct mdp_superblock_s / typedef mdp_super_t.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Neil Brown <neilb@xxxxxxx>
cc: linux-raid@xxxxxxxxxxxxxxx
---

 include/uapi/linux/raid/md_p.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/raid/md_p.h b/include/uapi/linux/raid/md_p.h
index ee75353..fe1a540 100644
--- a/include/uapi/linux/raid/md_p.h
+++ b/include/uapi/linux/raid/md_p.h
@@ -145,16 +145,18 @@ typedef struct mdp_superblock_s {
 	__u32 failed_disks;	/*  4 Number of failed disks		      */
 	__u32 spare_disks;	/*  5 Number of spare disks		      */
 	__u32 sb_csum;		/*  6 checksum of the whole superblock        */
-#ifdef __BIG_ENDIAN
+#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
 	__u32 events_hi;	/*  7 high-order of superblock update count   */
 	__u32 events_lo;	/*  8 low-order of superblock update count    */
 	__u32 cp_events_hi;	/*  9 high-order of checkpoint update count   */
 	__u32 cp_events_lo;	/* 10 low-order of checkpoint update count    */
-#else
+#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
 	__u32 events_lo;	/*  7 low-order of superblock update count    */
 	__u32 events_hi;	/*  8 high-order of superblock update count   */
 	__u32 cp_events_lo;	/*  9 low-order of checkpoint update count    */
 	__u32 cp_events_hi;	/* 10 high-order of checkpoint update count   */
+#else
+#error unspecified endianness
 #endif
 	__u32 recovery_cp;	/* 11 recovery checkpoint sector count	      */
 	/* There are only valid for minor_version > 90 */

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