[PATCH for-5.1 1/2] block: Require aligned image size to avoid assertion failure

[Kevin Wolf <kwolf@redhat.com>]

Unaligned requests will automatically be aligned to bl.request_alignment
and we don't want to extend requests to access space beyond the end of
the image, so it's required that the image size is aligned.

With write requests, this could cause assertion failures like this if
RESIZE permissions weren't requested:

qemu-img: block/io.c:1910: bdrv_co_write_req_prepare: Assertion `end_sector <= bs->total_sectors || child->perm & BLK_PERM_RESIZE' failed.

This was e.g. triggered by qemu-img converting to a target image with 4k
request alignment when the image was only aligned to 512 bytes, but not
to 4k.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/block.c b/block.c
index cc377d7ef3..c635777911 100644
--- a/block.c
+++ b/block.c
@@ -1489,6 +1489,16 @@ static int bdrv_open_driver(BlockDriverState *bs, BlockDriver *drv,
         return -EINVAL;
     }
 
+    /*
+     * Unaligned requests will automatically be aligned to bl.request_alignment
+     * and we don't want to extend requests to access space beyond the end of
+     * the image, so it's required that the image size is aligned.
+     */
+    if ((bs->total_sectors * BDRV_SECTOR_SIZE) % bs->bl.request_alignment) {
+        error_setg(errp, "Image size is not a multiple of request alignment");
+        return -EINVAL;
+    }
+
     assert(bdrv_opt_mem_align(bs) != 0);
     assert(bdrv_min_mem_align(bs) != 0);
     assert(is_power_of_2(bs->bl.request_alignment));
-- 
2.25.4