[PATCH 3/4] block/copy-before-write: implement cbw-timeout option

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

In some scenarios, when copy-before-write operations lasts too long
time, it's better to cancel it.

Most useful would be to use the new option together with
on-cbw-error=break-snapshot: this way if cbw operation takes too long
time we'll just cancel backup process but do not disturb the guest too
much.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 qapi/block-core.json      | 5 ++++-
 block/copy-before-write.c | 6 +++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index e5206272aa..78c77049c3 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -4204,12 +4204,15 @@
 # @on-cbw-error: Behavior on failure of copy-before-write operation.
 #                Default is @break-guest-write. (Since 7.0)
 #
+# @cbw-timeout: Zero means no limit. Non-zero sets the timeout in seconds
+#               for copy-before-write operation. Default 0. (Since 7.0)
+#
 # Since: 6.2
 ##
 { 'struct': 'BlockdevOptionsCbw',
   'base': 'BlockdevOptionsGenericFormat',
   'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap',
-            '*on-cbw-error': 'OnCbwError' } }
+            '*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32' } }
 
 ##
 # @BlockdevOptions:
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index e89cc9799c..50681cc711 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -42,6 +42,7 @@ typedef struct BDRVCopyBeforeWriteState {
     BlockCopyState *bcs;
     BdrvChild *target;
     OnCbwError on_cbw_error;
+    uint32_t cbw_timeout_ns;
 
     /*
      * @lock: protects access to @access_bitmap, @done_bitmap and
@@ -107,7 +108,7 @@ static coroutine_fn int cbw_do_copy_before_write(BlockDriverState *bs,
     off = QEMU_ALIGN_DOWN(offset, cluster_size);
     end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
 
-    ret = block_copy(s->bcs, off, end - off, true);
+    ret = block_copy(s->bcs, off, end - off, true, s->cbw_timeout_ns);
     if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) {
         return ret;
     }
@@ -405,6 +406,7 @@ static BlockdevOptionsCbw *cbw_parse_options(QDict *options, Error **errp)
      */
     qdict_extract_subqdict(options, NULL, "bitmap");
     qdict_del(options, "on-cbw-error");
+    qdict_del(options, "cbw-timeout");
 
 out:
     visit_free(v);
@@ -448,6 +450,8 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
     }
     s->on_cbw_error = opts->has_on_cbw_error ? opts->on_cbw_error :
             ON_CBW_ERROR_BREAK_GUEST_WRITE;
+    s->cbw_timeout_ns = opts->has_cbw_timeout ?
+        opts->cbw_timeout * NANOSECONDS_PER_SECOND : 0;
 
     bs->total_sectors = bs->file->bs->total_sectors;
     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
-- 
2.31.1