[Qemu-devel] [PATCH v4 09/10] block/blklogwrites: Use block limits from the backend block configuration

[Ari Sundholm <ari@tuxera.com>]

This is to ensure that writes are aligned properly for logging writes
to the virtual block device. This is important because the
dm-log-writes log format has a granularity of one sector for both the
offset and the size of each write. By using the logical sector size
for alignment, the log records the writes more faithfully for those
devices that have a non-512 logical sector size.

Note that even with this patch, blklogwrites still uses
BDRV_SECTOR_SIZE for logging. This will change in a subsequent patch
which will introduce support for non-512 sector sizes.

Signed-off-by: Ari Sundholm <ari@tuxera.com>
---
 block/blklogwrites.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/block/blklogwrites.c b/block/blklogwrites.c
index 1b969b0..216367f 100644
--- a/block/blklogwrites.c
+++ b/block/blklogwrites.c
@@ -173,6 +173,25 @@ static void blk_log_writes_refresh_limits(BlockDriverState *bs, Error **errp)
     }
 }
 
+static void blk_log_writes_apply_blkconf(BlockDriverState *bs, BlockConf *conf)
+{
+    assert(bs && conf && conf->blk);
+
+    bs->bl.request_alignment = conf->logical_block_size;
+    if (conf->discard_granularity != (uint32_t)-1) {
+        bs->bl.pdiscard_alignment = conf->discard_granularity;
+    }
+
+    if (bs->bl.pdiscard_alignment &&
+            bs->bl.pdiscard_alignment < bs->bl.request_alignment) {
+        bs->bl.pdiscard_alignment = bs->bl.request_alignment;
+    }
+    if (bs->bl.pwrite_zeroes_alignment &&
+            bs->bl.pwrite_zeroes_alignment < bs->bl.request_alignment) {
+        bs->bl.pwrite_zeroes_alignment = bs->bl.request_alignment;
+    }
+}
+
 static int coroutine_fn
 blk_log_writes_co_preadv(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
                          QEMUIOVector *qiov, int flags)
@@ -370,6 +389,7 @@ static BlockDriver bdrv_blk_log_writes = {
     .bdrv_refresh_filename  = blk_log_writes_refresh_filename,
     .bdrv_child_perm        = blk_log_writes_child_perm,
     .bdrv_refresh_limits    = blk_log_writes_refresh_limits,
+    .bdrv_apply_blkconf     = blk_log_writes_apply_blkconf,
 
     .bdrv_co_preadv         = blk_log_writes_co_preadv,
     .bdrv_co_pwritev        = blk_log_writes_co_pwritev,
-- 
2.7.4