Commits 04ed95f4 and 1a62d0ac updated the block layer to auto-fragment
any I/O to fit within device boundaries. Additionally, when using a
minimum alignment of 4k, we want to ensure the block layer does proper
read-modify-write rather than requesting I/O on a slice of a sector.
Let's enforce that the contract is obeyed when using blkdebug.  For
now, blkdebug only allows alignment overrides, and just inherits other
limits from whatever device it is wrapping, but a future patch will
further enhance things.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

---
v10: no change
v5-v9: no change
v4: no change
v3: rebase to byte-based interfaces
v2: new patch
---
 block/blkdebug.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/block/blkdebug.c b/block/blkdebug.c
index c795ae9..14d3fc5 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -431,6 +431,13 @@ blkdebug_co_preadv(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
     BDRVBlkdebugState *s = bs->opaque;
     BlkdebugRule *rule = NULL;

+    /* Sanity check block layer guarantees */
+    assert(QEMU_IS_ALIGNED(offset, bs->bl.request_alignment));
+    assert(QEMU_IS_ALIGNED(bytes, bs->bl.request_alignment));
+    if (bs->bl.max_transfer) {
+        assert(bytes <= bs->bl.max_transfer);
+    }
+
     QSIMPLEQ_FOREACH(rule, &s->active_rules, active_next) {
         uint64_t inject_offset = rule->options.inject.offset;

@@ -455,6 +462,13 @@ blkdebug_co_pwritev(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
     BDRVBlkdebugState *s = bs->opaque;
     BlkdebugRule *rule = NULL;

+    /* Sanity check block layer guarantees */
+    assert(QEMU_IS_ALIGNED(offset, bs->bl.request_alignment));
+    assert(QEMU_IS_ALIGNED(bytes, bs->bl.request_alignment));
+    if (bs->bl.max_transfer) {
+        assert(bytes <= bs->bl.max_transfer);
+    }
+
     QSIMPLEQ_FOREACH(rule, &s->active_rules, active_next) {
         uint64_t inject_offset = rule->options.inject.offset;

-- 
2.9.3