From f1bb39a8a5b6d486faa1a51a7f28c577155642c9 Mon Sep 17 00:00:00 2001 From: Vladimir Sementsov-Ogievskiy Date: Thu, 7 Apr 2022 16:27:21 +0300 Subject: block/copy-before-write: add on-cbw-error open parameter Currently, behavior on copy-before-write operation failure is simple: report error to the guest. Let's implement alternative behavior: break the whole copy-before-write process (and corresponding backup job or NBD client) but keep guest working. It's needed if we consider guest stability as more important. The realisation is simple: on copy-before-write failure we set s->snapshot_ret and continue guest operations. s->snapshot_ret being set will lead to all further snapshot API requests. Note that all in-flight snapshot-API requests may still success: we do wait for them on BREAK_SNAPSHOT-failure path in cbw_do_copy_before_write(). Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Signed-off-by: Vladimir Sementsov-Ogievskiy --- block/copy-before-write.c | 32 ++++++++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-) (limited to 'block') diff --git a/block/copy-before-write.c b/block/copy-before-write.c index e29c46c..c8a11a0 100644 --- a/block/copy-before-write.c +++ b/block/copy-before-write.c @@ -41,6 +41,7 @@ typedef struct BDRVCopyBeforeWriteState { BlockCopyState *bcs; BdrvChild *target; + OnCbwError on_cbw_error; /* * @lock: protects access to @access_bitmap, @done_bitmap and @@ -65,6 +66,14 @@ typedef struct BDRVCopyBeforeWriteState { * node. These areas must not be rewritten by guest. */ BlockReqList frozen_read_reqs; + + /* + * @snapshot_error is normally zero. But on first copy-before-write failure + * when @on_cbw_error == ON_CBW_ERROR_BREAK_SNAPSHOT, @snapshot_error takes + * value of this error (<0). After that all in-flight and further + * snapshot-API requests will fail with that error. + */ + int snapshot_error; } BDRVCopyBeforeWriteState; static coroutine_fn int cbw_co_preadv( @@ -95,16 +104,27 @@ static coroutine_fn int cbw_do_copy_before_write(BlockDriverState *bs, return 0; } + if (s->snapshot_error) { + return 0; + } + off = QEMU_ALIGN_DOWN(offset, cluster_size); end = QEMU_ALIGN_UP(offset + bytes, cluster_size); ret = block_copy(s->bcs, off, end - off, true); - if (ret < 0) { + if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) { return ret; } WITH_QEMU_LOCK_GUARD(&s->lock) { - bdrv_set_dirty_bitmap(s->done_bitmap, off, end - off); + if (ret < 0) { + assert(s->on_cbw_error == ON_CBW_ERROR_BREAK_SNAPSHOT); + if (!s->snapshot_error) { + s->snapshot_error = ret; + } + } else { + bdrv_set_dirty_bitmap(s->done_bitmap, off, end - off); + } reqlist_wait_all(&s->frozen_read_reqs, off, end - off, &s->lock); } @@ -176,6 +196,11 @@ static BlockReq *cbw_snapshot_read_lock(BlockDriverState *bs, QEMU_LOCK_GUARD(&s->lock); + if (s->snapshot_error) { + g_free(req); + return NULL; + } + if (bdrv_dirty_bitmap_next_zero(s->access_bitmap, offset, bytes) != -1) { g_free(req); return NULL; @@ -351,6 +376,7 @@ static BlockdevOptions *cbw_parse_options(QDict *options, Error **errp) * object for original options. */ qdict_extract_subqdict(options, NULL, "bitmap"); + qdict_del(options, "on-cbw-error"); out: visit_free(v); @@ -395,6 +421,8 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags, return -EINVAL; } } + s->on_cbw_error = opts->has_on_cbw_error ? opts->on_cbw_error : + ON_CBW_ERROR_BREAK_GUEST_WRITE; bs->total_sectors = bs->file->bs->total_sectors; bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED | -- cgit v1.1