block: eliminate BDRV_REQ_NO_SERIALISING

It is unused since commit 00e30f0 ("block/backup: use backup-top instead
of write notifiers", 2019-10-01), drop it to simplify the code.

While at it, drop redundant assertions on flags.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1578495356-46219-2-git-send-email-pbonzini@redhat.com
Message-Id: <1578495356-46219-2-git-send-email-pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/io.c

@@ -1445,8 +1445,7 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
      * potential fallback support, if we ever implement any read flags
      * to pass through to drivers.  For now, there aren't any
      * passthrough flags.  */
-    assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ |
-                       BDRV_REQ_PREFETCH)));
+    assert(!(flags & ~(BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH)));
 
     /* Handle Copy on Read and associated serialisation */
     if (flags & BDRV_REQ_COPY_ON_READ) {
@@ -1458,12 +1457,7 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
         bdrv_mark_request_serialising(req, bdrv_get_cluster_size(bs));
     }
 
-    /* BDRV_REQ_SERIALISING is only for write operation */
-    assert(!(flags & BDRV_REQ_SERIALISING));
-
-    if (!(flags & BDRV_REQ_NO_SERIALISING)) {
-        bdrv_wait_serialising_requests(req);
-    }
+    bdrv_wait_serialising_requests(req);
 
     if (flags & BDRV_REQ_COPY_ON_READ) {
         int64_t pnum;
@@ -1711,7 +1705,7 @@ int coroutine_fn bdrv_co_preadv_part(BdrvChild *child,
     bdrv_inc_in_flight(bs);
 
     /* Don't do copy-on-read if we read data before write operation */
-    if (atomic_read(&bs->copy_on_read) && !(flags & BDRV_REQ_NO_SERIALISING)) {
+    if (atomic_read(&bs->copy_on_read)) {
         flags |= BDRV_REQ_COPY_ON_READ;
     }
 
@@ -1852,8 +1846,6 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, uint64_t bytes,
         return -EPERM;
     }
 
-    /* BDRV_REQ_NO_SERIALISING is only for read operation */
-    assert(!(flags & BDRV_REQ_NO_SERIALISING));
     assert(!(bs->open_flags & BDRV_O_INACTIVE));
     assert((bs->open_flags & BDRV_O_NO_IO) == 0);
     assert(!(flags & ~BDRV_REQ_MASK));
@@ -3222,9 +3214,7 @@ static int coroutine_fn bdrv_co_copy_range_internal(
 
         /* BDRV_REQ_SERIALISING is only for write operation */
         assert(!(read_flags & BDRV_REQ_SERIALISING));
-        if (!(read_flags & BDRV_REQ_NO_SERIALISING)) {
-            bdrv_wait_serialising_requests(&req);
-        }
+        bdrv_wait_serialising_requests(&req);
 
         ret = src->bs->drv->bdrv_co_copy_range_from(src->bs,
                                                     src, src_offset,

include/block/block.h

@@ -51,18 +51,6 @@ typedef enum {
      */
     BDRV_REQ_MAY_UNMAP          = 0x4,
 
-    /*
-     * The BDRV_REQ_NO_SERIALISING flag is only valid for reads and means that
-     * we don't want wait_serialising_requests() during the read operation.
-     *
-     * This flag is used for backup copy-on-write operations, when we need to
-     * read old data before write (write notifier triggered). It is okay since
-     * we already waited for other serializing requests in the initiating write
-     * (see bdrv_aligned_pwritev), and it is necessary if the initiating write
-     * is already serializing (without the flag, the read would deadlock
-     * waiting for the serialising write to complete).
-     */
-    BDRV_REQ_NO_SERIALISING     = 0x8,
     BDRV_REQ_FUA                = 0x10,
     BDRV_REQ_WRITE_COMPRESSED   = 0x20,