For older mdadm version, v1.x metadata has different bitmap_offset,
we can't ensure all the bitmaps are on a 4K boundary since writing
4K for bitmap could corrupt the superblock, and Anthony reported
the bug about it at below link.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=837964
So let's check about the alignment for bitmap_offset before set
the boundary to 4096 unconditionally. Thanks for Neil's detailed
explanation.
Reported-by: Anthony DeRobertis <redacted>
Fixes: 95a05b37e8eb ("Create n bitmaps for clustered mode")
Cc: Neil Brown <redacted>
Signed-off-by: Guoqing Jiang <redacted>
---
super1.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/super1.c b/super1.c
index 9f62d23..4fef378 100644
--- a/super1.c
+++ b/super1.c
@@ -2433,7 +2433,15 @@ static int write_bitmap1(struct supertype *st, int fd, enum bitmap_update update
memset(buf, 0xff, 4096);
memcpy(buf, (char *)bms, sizeof(bitmap_super_t));
- towrite = calc_bitmap_size(bms, 4096);
+ /*
+ * use 4096 boundary if bitmap_offset is aligned
+ * with 8 sectors, then it should compatible with
+ * older mdadm.
+ */
+ if (__le32_to_cpu(sb->bitmap_offset) & 7)
+ towrite = calc_bitmap_size(bms, 512);
+ else
+ towrite = calc_bitmap_size(bms, 4096);
while (towrite > 0) {
n = towrite;
if (n > 4096)--
2.6.6