block/mirror: determine copy_to_target only once

In preparation to allow changing the copy_mode via QMP. When running
in an iothread, it could be that copy_mode is changed from the main
thread in between reading copy_mode in bdrv_mirror_top_pwritev() and
reading copy_mode in bdrv_mirror_top_do_write(), so they might end up
disagreeing about whether copy_to_target is true or false. Avoid that
scenario by determining copy_to_target only once and passing it to
bdrv_mirror_top_do_write() as an argument.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20231031135431.393137-5-f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 18 insertions, 23 deletions

diff --git a/block/mirror.c b/block/mirror.c
index 914d723..31da152 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1463,21 +1463,21 @@ bdrv_mirror_top_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
     return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
 }
 
+static bool should_copy_to_target(MirrorBDSOpaque *s)
+{
+    return s->job && s->job->ret >= 0 &&
+        !job_is_cancelled(&s->job->common.job) &&
+        s->job->copy_mode == MIRROR_COPY_MODE_WRITE_BLOCKING;
+}
+
 static int coroutine_fn GRAPH_RDLOCK
 bdrv_mirror_top_do_write(BlockDriverState *bs, MirrorMethod method,
-                         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov,
-                         int flags)
+                         bool copy_to_target, uint64_t offset, uint64_t bytes,
+                         QEMUIOVector *qiov, int flags)
 {
     MirrorOp *op = NULL;
     MirrorBDSOpaque *s = bs->opaque;
     int ret = 0;
-    bool copy_to_target = false;
-
-    if (s->job) {
-        copy_to_target = s->job->ret >= 0 &&
-                         !job_is_cancelled(&s->job->common.job) &&
-                         s->job->copy_mode == MIRROR_COPY_MODE_WRITE_BLOCKING;
-    }
 
     if (copy_to_target) {
         op = active_write_prepare(s->job, offset, bytes);
@@ -1524,17 +1524,10 @@ static int coroutine_fn GRAPH_RDLOCK
 bdrv_mirror_top_pwritev(BlockDriverState *bs, int64_t offset, int64_t bytes,
                         QEMUIOVector *qiov, BdrvRequestFlags flags)
 {
-    MirrorBDSOpaque *s = bs->opaque;
     QEMUIOVector bounce_qiov;
     void *bounce_buf;
     int ret = 0;
-    bool copy_to_target = false;
-
-    if (s->job) {
-        copy_to_target = s->job->ret >= 0 &&
-                         !job_is_cancelled(&s->job->common.job) &&
-                         s->job->copy_mode == MIRROR_COPY_MODE_WRITE_BLOCKING;
-    }
+    bool copy_to_target = should_copy_to_target(bs->opaque);
 
     if (copy_to_target) {
         /* The guest might concurrently modify the data to write; but
@@ -1551,8 +1544,8 @@ bdrv_mirror_top_pwritev(BlockDriverState *bs, int64_t offset, int64_t bytes,
         flags &= ~BDRV_REQ_REGISTERED_BUF;
     }
 
-    ret = bdrv_mirror_top_do_write(bs, MIRROR_METHOD_COPY, offset, bytes, qiov,
-                                   flags);
+    ret = bdrv_mirror_top_do_write(bs, MIRROR_METHOD_COPY, copy_to_target,
+                                   offset, bytes, qiov, flags);
 
     if (copy_to_target) {
         qemu_iovec_destroy(&bounce_qiov);
@@ -1575,15 +1568,17 @@ static int coroutine_fn GRAPH_RDLOCK
 bdrv_mirror_top_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
                               int64_t bytes, BdrvRequestFlags flags)
 {
-    return bdrv_mirror_top_do_write(bs, MIRROR_METHOD_ZERO, offset, bytes, NULL,
-                                    flags);
+    bool copy_to_target = should_copy_to_target(bs->opaque);
+    return bdrv_mirror_top_do_write(bs, MIRROR_METHOD_ZERO, copy_to_target,
+                                    offset, bytes, NULL, flags);
 }
 
 static int coroutine_fn GRAPH_RDLOCK
 bdrv_mirror_top_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
 {
-    return bdrv_mirror_top_do_write(bs, MIRROR_METHOD_DISCARD, offset, bytes,
-                                    NULL, 0);
+    bool copy_to_target = should_copy_to_target(bs->opaque);
+    return bdrv_mirror_top_do_write(bs, MIRROR_METHOD_DISCARD, copy_to_target,
+                                    offset, bytes, NULL, 0);
 }
 
 static void bdrv_mirror_top_refresh_filename(BlockDriverState *bs)