[Ocfs2-tools-devel] [PATCH 1/3] O2image: A potential bug in o2image.

[Tristan Ye]

Currently, we're using a scaling-down strategy to alloc memory chunk
for o2image's bitmap blocks, the unerdyling alloc function which we
were using(ocfs2_malloc_blocks) treat channel_io_blksz as basic unit.
which may be smaller than our OCFS2_IMAGE_BITMAP_BLOCKSIZE(512 vs 4096).

As a result, the problem is we're probably going to miss some blocks to allocate
if the actual allocsize is not a multiple of OCFS2_IMAGE_BITMAP_BLOCKSIZE.

Say we have 4096 * 17(bitmap blocks) to allocate, and failed at the first attemp,
while did succeed after trying 'allocsize >>1', actually '2048 * 17' only fills up
8 image bitmap blocks, therefore, we get 16 image bitmap blocks allocated eventually.
Now one block was missed.

I guess it's very likely to hit if the number of bitmap blocks is odd, am I understanding
incorrectly?

Signed-off-by: Tristan Ye <tristan.ye at oracle.com>
---
 libocfs2/image.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/libocfs2/image.c b/libocfs2/image.c
index 0a1eeb8..49693f2 100644
--- a/libocfs2/image.c
+++ b/libocfs2/image.c
@@ -122,6 +122,10 @@ errcode_t ocfs2_image_alloc_bitmap(ocfs2_filesys *ofs)
 			if (allocsize == OCFS2_IMAGE_BITMAP_BLOCKSIZE)
 				goto out;
 			allocsize >>= 1;
+			if (allocsize % OCFS2_IMAGE_BITMAP_BLOCKSIZE) {
+				allocsize /= OCFS2_IMAGE_BITMAP_BLOCKSIZE;
+				allocsize *= OCFS2_IMAGE_BITMAP_BLOCKSIZE;
+			}
 			continue;
 		}
 
@@ -138,6 +142,8 @@ errcode_t ocfs2_image_alloc_bitmap(ocfs2_filesys *ofs)
 			indx++;
 		}
 		leftsize -= allocsize;
+		if (leftsize <= allocsize);
+			allocsize = leftsize;
 	}
 out:
 	/* If allocation failed free and return error */
-- 
1.5.5