block/copy-before-write: implement cbw-timeout option
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.
Note the tricky point of realization: we keep additional point in
bs->in_flight during block_copy operation even if it's timed-out.
Background "cancelled" block_copy operations will finish at some point
and will want to access state. We should care to not free the state in
.bdrv_close() earlier.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
[vsementsov: use bdrv_inc_in_flight()/bdrv_dec_in_flight() instead of
direct manipulation on bs->in_flight]
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index fc13c7c..c24b8dd 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -42,6 +42,7 @@
BlockCopyState *bcs;
BdrvChild *target;
OnCbwError on_cbw_error;
+ uint32_t cbw_timeout_ns;
/*
* @lock: protects access to @access_bitmap, @done_bitmap and
@@ -83,6 +84,13 @@
return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
}
+static void block_copy_cb(void *opaque)
+{
+ BlockDriverState *bs = opaque;
+
+ bdrv_dec_in_flight(bs);
+}
+
/*
* Do copy-before-write operation.
*
@@ -111,7 +119,16 @@
off = QEMU_ALIGN_DOWN(offset, cluster_size);
end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
- ret = block_copy(s->bcs, off, end - off, true, 0, NULL, NULL);
+ /*
+ * Increase in_flight, so that in case of timed-out block-copy, the
+ * remaining background block_copy() request (which can't be immediately
+ * cancelled by timeout) is presented in bs->in_flight. This way we are
+ * sure that on bs close() we'll previously wait for all timed-out but yet
+ * running block_copy calls.
+ */
+ bdrv_inc_in_flight(bs);
+ ret = block_copy(s->bcs, off, end - off, true, s->cbw_timeout_ns,
+ block_copy_cb, bs);
if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) {
return ret;
}
@@ -377,6 +394,7 @@
*/
qdict_extract_subqdict(options, NULL, "bitmap");
qdict_del(options, "on-cbw-error");
+ qdict_del(options, "cbw-timeout");
out:
visit_free(v);
@@ -423,6 +441,8 @@
}
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 |
