[PATCH] super1: make write_bitmap1 compatible with previous mdadm versions

* [PATCH] super1: make write_bitmap1 compatible with previous mdadm versions
@ 2016-10-12  6:24 Guoqing Jiang
  2016-10-19 15:21 ` Jes Sorensen
  0 siblings, 1 reply; 2+ messages in thread
From: Guoqing Jiang @ 2016-10-12  6:24 UTC (permalink / raw)
  To: Jes.Sorensen; +Cc: linux-raid, Guoqing Jiang, Neil Brown

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 <anthony@derobert.net>
Fixes: 95a05b37e8eb ("Create n bitmaps for clustered mode")
Cc: Neil Brown <neilb@suse.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
---
 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


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