From 6db7fd1ca980f8dd2fd082f13613166e170afd05 Mon Sep 17 00:00:00 2001 From: Vladimir Sementsov-Ogievskiy Date: Thu, 7 Apr 2022 16:27:25 +0300 Subject: [PATCH] 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 Reviewed-by: Hanna Reitz [vsementsov: use bdrv_inc_in_flight()/bdrv_dec_in_flight() instead of direct manipulation on bs->in_flight] Signed-off-by: Vladimir Sementsov-Ogievskiy --- block/copy-before-write.c | 22 +++++++++++++++++++++- qapi/block-core.json | 8 +++++++- 2 files changed, 28 insertions(+), 2 deletions(-) diff --git a/block/copy-before-write.c b/block/copy-before-write.c index fc13c7cd44..c24b8dd117 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 @@ -83,6 +84,13 @@ static coroutine_fn int cbw_co_preadv( 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 @@ 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, 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 @@ static BlockdevOptions *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); @@ -423,6 +441,8 @@ 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 | diff --git a/qapi/block-core.json b/qapi/block-core.json index 3e8456a94a..2173e7734a 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -4227,12 +4227,18 @@ # @on-cbw-error: Behavior on failure of copy-before-write operation. # Default is @break-guest-write. (Since 7.1) # +# @cbw-timeout: Zero means no limit. Non-zero sets the timeout in seconds +# for copy-before-write operation. When a timeout occurs, +# the respective copy-before-write operation will fail, and +# the @on-cbw-error parameter will decide how this failure +# is handled. Default 0. (Since 7.1) +# # Since: 6.2 ## { 'struct': 'BlockdevOptionsCbw', 'base': 'BlockdevOptionsGenericFormat', 'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap', - '*on-cbw-error': 'OnCbwError' } } + '*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32' } } ## # @BlockdevOptions: -- 2.11.4.GIT