[PATCH 3/3] bcachefs: use swab40 for bch_backpointer.bucket_offset bitfield

[Brian Foster <bfoster@redhat.com>]

The bucket_offset field of bch_backpointer is a 40-bit bitfield, but the
bch2_backpointer_swab() helper uses swab32. This leads to inconsistency
when an on-disk fs is accessed from an opposite endian machine.

As it turns out, we already have an internal swab40() helper that is
used from the bch_alloc_v4 swab callback. Lift it into the backpointers
header file and use it consistently in both places.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/bcachefs/alloc_background.c | 9 ---------
 fs/bcachefs/backpointers.c     | 2 +-
 fs/bcachefs/backpointers.h     | 9 +++++++++
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/bcachefs/alloc_background.c b/fs/bcachefs/alloc_background.c
index ad256a88cb5c..1fec0e67891f 100644
--- a/fs/bcachefs/alloc_background.c
+++ b/fs/bcachefs/alloc_background.c
@@ -297,15 +297,6 @@ int bch2_alloc_v4_invalid(struct bch_fs *c, struct bkey_s_c k,
 	return ret;
 }
 
-static inline u64 swab40(u64 x)
-{
-	return (((x & 0x00000000ffULL) << 32)|
-		((x & 0x000000ff00ULL) << 16)|
-		((x & 0x0000ff0000ULL) >>  0)|
-		((x & 0x00ff000000ULL) >> 16)|
-		((x & 0xff00000000ULL) >> 32));
-}
-
 void bch2_alloc_v4_swab(struct bkey_s k)
 {
 	struct bch_alloc_v4 *a = bkey_s_to_alloc_v4(k).v;
diff --git a/fs/bcachefs/backpointers.c b/fs/bcachefs/backpointers.c
index 3b79bde1ce2f..5ed96dddae08 100644
--- a/fs/bcachefs/backpointers.c
+++ b/fs/bcachefs/backpointers.c
@@ -77,7 +77,7 @@ void bch2_backpointer_swab(struct bkey_s k)
 {
 	struct bkey_s_backpointer bp = bkey_s_to_backpointer(k);
 
-	bp.v->bucket_offset	= swab32(bp.v->bucket_offset);
+	bp.v->bucket_offset	= swab40(bp.v->bucket_offset);
 	bp.v->bucket_len	= swab32(bp.v->bucket_len);
 	bch2_bpos_swab(&bp.v->pos);
 }
diff --git a/fs/bcachefs/backpointers.h b/fs/bcachefs/backpointers.h
index 4ab9f3562912..ab866feeaf66 100644
--- a/fs/bcachefs/backpointers.h
+++ b/fs/bcachefs/backpointers.h
@@ -7,6 +7,15 @@
 #include "buckets.h"
 #include "super.h"
 
+static inline u64 swab40(u64 x)
+{
+	return (((x & 0x00000000ffULL) << 32)|
+		((x & 0x000000ff00ULL) << 16)|
+		((x & 0x0000ff0000ULL) >>  0)|
+		((x & 0x00ff000000ULL) >> 16)|
+		((x & 0xff00000000ULL) >> 32));
+}
+
 int bch2_backpointer_invalid(struct bch_fs *, struct bkey_s_c k,
 			     enum bkey_invalid_flags, struct printbuf *);
 void bch2_backpointer_to_text(struct printbuf *, const struct bch_backpointer *);
-- 
2.41.0