block: add bdrv_graph_wrlock_drained() convenience wrapper

Many write-locked sections are also drained sections. A new
bdrv_graph_wrunlock_drained() wrapper around bdrv_graph_wrunlock() is
introduced, which will begin a drained section first. A global
variable is used so bdrv_graph_wrunlock() knows if it also needs
to end such a drained section. Both the aio_poll call in
bdrv_graph_wrlock() and the aio_bh_poll() in bdrv_graph_wrunlock()
can re-enter a write-locked section. While for the latter, ending the
drain could be moved to before the call, the former requires that the
variable is a counter and not just a boolean.

Since the wrapper calls bdrv_drain_all_begin(), which must be called
with the graph unlocked, mark the wrapper as GRAPH_UNLOCKED too.

The switch to the new helpers was generated with the following
commands and then manually checked:
find . -name '*.c' -exec sed -i -z 's/bdrv_drain_all_begin();\n\s*bdrv_graph_wrlock();/bdrv_graph_wrlock_drained();/g' {} ';'
find . -name '*.c' -exec sed -i -z 's/bdrv_graph_wrunlock();\n\s*bdrv_drain_all_end();/bdrv_graph_wrunlock();/g' {} ';'

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20250530151125.955508-25-f.ebner@proxmox.com>
[kwolf: Removed redundant GRAPH_UNLOCKED]
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 15 deletions

diff --git a/tests/unit/test-bdrv-graph-mod.c b/tests/unit/test-bdrv-graph-mod.c
index 7b03ebe4b0..b077f0e3e3 100644
--- a/tests/unit/test-bdrv-graph-mod.c
+++ b/tests/unit/test-bdrv-graph-mod.c
@@ -137,12 +137,10 @@ static void test_update_perm_tree(void)
 
     blk_insert_bs(root, bs, &error_abort);
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     bdrv_attach_child(filter, bs, "child", &child_of_bds,
                       BDRV_CHILD_DATA, &error_abort);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     ret = bdrv_append(filter, bs, NULL);
     g_assert_cmpint(ret, <, 0);
@@ -206,13 +204,11 @@ static void test_should_update_child(void)
 
     bdrv_set_backing_hd(target, bs, &error_abort);
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     g_assert(target->backing->bs == bs);
     bdrv_attach_child(filter, target, "target", &child_of_bds,
                       BDRV_CHILD_DATA, &error_abort);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
     bdrv_append(filter, bs, &error_abort);
 
     bdrv_graph_rdlock_main_loop();
@@ -248,8 +244,7 @@ static void test_parallel_exclusive_write(void)
     bdrv_ref(base);
     bdrv_ref(fl1);
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     bdrv_attach_child(top, fl1, "backing", &child_of_bds,
                       BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
                       &error_abort);
@@ -262,7 +257,6 @@ static void test_parallel_exclusive_write(void)
 
     bdrv_replace_node(fl1, fl2, &error_abort);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     bdrv_drained_end(fl2);
     bdrv_drained_end(fl1);
@@ -369,8 +363,7 @@ static void test_parallel_perm_update(void)
      */
     bdrv_ref(base);
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     bdrv_attach_child(top, ws, "file", &child_of_bds, BDRV_CHILD_DATA,
                       &error_abort);
     c_fl1 = bdrv_attach_child(ws, fl1, "first", &child_of_bds,
@@ -384,7 +377,6 @@ static void test_parallel_perm_update(void)
                       BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
                       &error_abort);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     /* Select fl1 as first child to be active */
     s->selected = c_fl1;
@@ -438,13 +430,11 @@ static void test_append_greedy_filter(void)
     BlockDriverState *base = no_perm_node("base");
     BlockDriverState *fl = exclusive_writer_node("fl1");
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     bdrv_attach_child(top, base, "backing", &child_of_bds,
                       BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
                       &error_abort);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     bdrv_append(fl, base, &error_abort);
     bdrv_unref(fl);