[PATCH 02/12] virtio-blk: do not merge writes across a zone boundary

[Niklas Cassel <cassel@kernel.org>]

From: Sam Li <faithilikerun@gmail.com>

virtio_blk_submit_multireq() fuses adjacent in-zone requests into a
single request. On a zoned backend, a merged zone append request
that straddles a zone boundary is rejected by the device because
each write must stay within a single zone.

Add a bail condition to the merge coalescer: if combining the
candidate request into the current batch would cross a zone
boundary, flush the current batch and start a new one.

Signed-off-by: Sam Li <faithilikerun@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 block/block-backend.c             | 11 +++++++++++
 hw/block/virtio-blk.c             | 22 +++++++++++++++++++++-
 include/system/block-backend-io.h |  1 +
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index 37ba7e9fc4..049e70ddcb 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -2326,6 +2326,17 @@ uint32_t blk_get_request_alignment(BlockBackend *blk)
     return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE;
 }
 
+/*
+ * Returns the zone size in bytes for a zoned backend, or 0 if @blk does
+ * not present zoned geometry.
+ */
+uint64_t blk_get_zone_size(BlockBackend *blk)
+{
+    BlockDriverState *bs = blk_bs(blk);
+    IO_CODE();
+    return bs ? bs->bl.zone_size : 0;
+}
+
 /* Returns the optimal write zeroes alignment, in bytes; guaranteed nonzero */
 uint32_t blk_get_pwrite_zeroes_alignment(BlockBackend *blk)
 {
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 6b92066aff..f74cc3dbd0 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -294,6 +294,9 @@ static void virtio_blk_submit_multireq(VirtIOBlock *s, MultiReqBuffer *mrb)
     int i = 0, start = 0, num_reqs = 0, niov = 0, nb_sectors = 0;
     uint32_t max_transfer;
     int64_t sector_num = 0;
+    uint64_t zone_size = blk_get_zone_size(s->blk);
+    bool zone_cross;
+    int64_t zone_sector, end_sector;
 
     if (mrb->num_reqs == 1) {
         submit_requests(s, mrb, 0, 1, -1);
@@ -309,17 +312,34 @@ static void virtio_blk_submit_multireq(VirtIOBlock *s, MultiReqBuffer *mrb)
     for (i = 0; i < mrb->num_reqs; i++) {
         VirtIOBlockReq *req = mrb->reqs[i];
         if (num_reqs > 0) {
+            zone_cross = false;
+
+            /*
+             * On zoned backends, a single backend write/read must not span
+             * a zone boundary. Bail out of merging if combining req into
+             * the current batch would straddle a zone.
+             */
+            if (zone_size > 0) {
+                zone_sector = zone_size / BDRV_SECTOR_SIZE;
+                end_sector = req->sector_num
+                                + req->qiov.size / BDRV_SECTOR_SIZE - 1;
+                zone_cross = (sector_num / zone_sector) !=
+                             (end_sector / zone_sector);
+            }
+
             /*
              * NOTE: We cannot merge the requests in below situations:
              * 1. requests are not sequential
              * 2. merge would exceed maximum number of IOVs
              * 3. merge would exceed maximum transfer length of backend device
+             * 4. merge would cross a zone boundary on a zoned backend
              */
             if (sector_num + nb_sectors != req->sector_num ||
                 niov > blk_get_max_iov(s->blk) - req->qiov.niov ||
                 req->qiov.size > max_transfer ||
                 nb_sectors > (max_transfer -
-                              req->qiov.size) / BDRV_SECTOR_SIZE) {
+                              req->qiov.size) / BDRV_SECTOR_SIZE ||
+                zone_cross) {
                 submit_requests(s, mrb, start, num_reqs, niov);
                 num_reqs = 0;
             }
diff --git a/include/system/block-backend-io.h b/include/system/block-backend-io.h
index fd84723d9d..78d410b8df 100644
--- a/include/system/block-backend-io.h
+++ b/include/system/block-backend-io.h
@@ -121,6 +121,7 @@ uint32_t blk_get_request_alignment(BlockBackend *blk);
 uint32_t blk_get_pwrite_zeroes_alignment(BlockBackend *blk);
 uint32_t blk_get_max_transfer(BlockBackend *blk);
 uint64_t blk_get_max_hw_transfer(BlockBackend *blk);
+uint64_t blk_get_zone_size(BlockBackend *blk);
 
 int coroutine_fn blk_co_copy_range(BlockBackend *blk_in, int64_t off_in,
                                    BlockBackend *blk_out, int64_t off_out,
-- 
2.55.0