Am 19.09.2019 um 11:05 hat Pavel Dovgalyuk geschrieben: > > From: Kevin Wolf [mailto:kw...@redhat.com] > > > > > > > > However, global -snapshot is just a convenient shortcut for specifying > > > > snapshot=on for all -drive arguments. So if -snapshot is incompatible > > > > with replay, shouldn't manually marking all drives as snapshot=on be > > > > incompatible as well? > > > > > > > > Maybe you're really interested in some specific drive not having > > > > snapshot=on? But then it might be better to check that specific drive > > > > instad of forbidding just the shortcut for setting it. > > > > > > -snapshot adds the flag for top-level drive, making driver operations > > > dependent on temporary file structure. > > > > > > Moving this overlay beneath blkreplay driver makes drive operations > > > deterministic for the top-level device. > > > > So the real requirement is that blkreplay is the top-level node of any > > guest device, right? And only because of this, you can't use -snapshot > > (or snapshot=on on the blkreplay driver). > > > > If we instead check e.g. in blk_insert_bs() or blk_attach_dev() that in > > record/replay mode, the root node of the BlockBackend is blkreplay, > > wouldn't we catch many more incorrect setups? > > That sounds interesting. > Will it help to check that every backend is connected to blkreplay?
Yes, it would return an error when you try to attach a non-blkreplay node to a BlockBackend (and every guest device uses a BlockBackend). Note that this restriction would currently make block jobs unavailable on non-blkreplay nodes as they also use BlockBackends internally (though this is going to change in the long run). I believe this restriction is harmless and the typical replay use case doesn't involve any block jobs, but if you do think it's a problem, blk_attach_dev() would be the place that affects only devices. > How then this check has to be done? Only compile-tested, but maybe something like below? Kevin diff --git a/include/block/block_int.h b/include/block/block_int.h index 0422acdf1c..9fa72bea51 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -955,6 +955,7 @@ static inline BlockDriverState *backing_bs(BlockDriverState *bs) extern BlockDriver bdrv_file; extern BlockDriver bdrv_raw; extern BlockDriver bdrv_qcow2; +extern BlockDriver bdrv_blkreplay; int coroutine_fn bdrv_co_preadv(BdrvChild *child, int64_t offset, unsigned int bytes, QEMUIOVector *qiov, diff --git a/block/blkreplay.c b/block/blkreplay.c index 2b7931b940..16a4f1df6a 100644 --- a/block/blkreplay.c +++ b/block/blkreplay.c @@ -126,7 +126,7 @@ static int coroutine_fn blkreplay_co_flush(BlockDriverState *bs) return ret; } -static BlockDriver bdrv_blkreplay = { +BlockDriver bdrv_blkreplay = { .format_name = "blkreplay", .instance_size = 0, diff --git a/block/block-backend.c b/block/block-backend.c index 1c605d5444..c57d3d9fdf 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -17,6 +17,7 @@ #include "block/throttle-groups.h" #include "hw/qdev-core.h" #include "sysemu/blockdev.h" +#include "sysemu/replay.h" #include "sysemu/runstate.h" #include "qapi/error.h" #include "qapi/qapi-events-block.h" @@ -808,6 +809,12 @@ void blk_remove_bs(BlockBackend *blk) int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs, Error **errp) { ThrottleGroupMember *tgm = &blk->public.throttle_group_member; + + if (replay_mode != REPLAY_MODE_NONE && bs->drv != &bdrv_blkreplay) { + error_setg(errp, "Root node must be blkreplay"); + return -ENOTSUP; + } + bdrv_ref(bs); blk->root = bdrv_root_attach_child(bs, "root", &child_root, blk->ctx, blk->perm, blk->shared_perm, blk, errp);