[PULL,10/30] block: introduce BDRV_REQ_NO_WAIT flag

Commit Message

Max Reitz Dec. 18, 2020, 3:12 p.m. UTC

From: Vladimir Sementsov-Ogievskiy <[e-mail]>

Add flag to make serialising request no wait: if there are conflicting
requests, just return error immediately. It's will be used in upcoming
preallocate filter.

Signed-off-by: Vladimir Sementsov-Ogievskiy <[e-mail]>
Reviewed-by: Max Reitz <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Max Reitz <[e-mail]>
---
 include/block/block.h |  9 ++++++++-
 block/io.c            | 11 ++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

Patch

diff --git a/include/block/block.h b/include/block/block.h
index a3f3dcc88f..a193545b6a 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -77,8 +77,15 @@  typedef enum {
      * written to qiov parameter which may be NULL.
      */
     BDRV_REQ_PREFETCH  = 0x200,
+
+    /*
+     * If we need to wait for other requests, just fail immediately. Used
+     * only together with BDRV_REQ_SERIALISING.
+     */
+    BDRV_REQ_NO_WAIT = 0x400,
+
     /* Mask of valid flags */
-    BDRV_REQ_MASK               = 0x3ff,
+    BDRV_REQ_MASK               = 0x7ff,
 } BdrvRequestFlags;
 
 typedef struct BlockSizes {
diff --git a/block/io.c b/block/io.c
index fadfed3ab8..95b1c56c06 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1858,9 +1858,18 @@  bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, uint64_t bytes,
     assert(!(bs->open_flags & BDRV_O_INACTIVE));
     assert((bs->open_flags & BDRV_O_NO_IO) == 0);
     assert(!(flags & ~BDRV_REQ_MASK));
+    assert(!((flags & BDRV_REQ_NO_WAIT) && !(flags & BDRV_REQ_SERIALISING)));
 
     if (flags & BDRV_REQ_SERIALISING) {
-        bdrv_make_request_serialising(req, bdrv_get_cluster_size(bs));
+        QEMU_LOCK_GUARD(&bs->reqs_lock);
+
+        tracked_request_set_serialising(req, bdrv_get_cluster_size(bs));
+
+        if ((flags & BDRV_REQ_NO_WAIT) && bdrv_find_conflicting_request(req)) {
+            return -EBUSY;
+        }
+
+        bdrv_wait_serialising_requests_locked(req);
     } else {
         bdrv_wait_serialising_requests(req);
     }