From: "Pavel Dovgalyuk" <dovgaluk@ispras.ru>
To: "'Kevin Wolf'" <kwolf@redhat.com>
Cc: peter.maydell@linaro.org, pavel.dovgaluk@ispras.ru,
quintela@redhat.com, ciro.santilli@gmail.com,
jasowang@redhat.com, crosthwaite.peter@gmail.com,
qemu-devel@nongnu.org, armbru@redhat.com, alex.bennee@linaro.org,
maria.klimushenkova@ispras.ru, mst@redhat.com, kraxel@redhat.com,
boost.lists@gmail.com, thomas.dullien@googlemail.com,
pbonzini@redhat.com, mreitz@redhat.com,
artem.k.pisarenko@gmail.com, dgilbert@redhat.com,
rth@twiddle.net
Subject: Re: [Qemu-devel] [for-4.2 PATCH 3/6] replay: update docs for record/replay with block devices
Date: Thu, 19 Sep 2019 15:10:43 +0300 [thread overview]
Message-ID: <001a01d56ee3$4354a530$c9fdef90$@ru> (raw)
In-Reply-To: <20190919112702.GC10163@localhost.localdomain>
> From: Kevin Wolf [mailto:kwolf@redhat.com]
> Am 19.09.2019 um 11:05 hat Pavel Dovgalyuk geschrieben:
> > > From: Kevin Wolf [mailto:kwolf@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;
> + }
I guess this is opposite direction - bs->drv is bdrv_file.
And we should check its parent.
> +
> bdrv_ref(bs);
> blk->root = bdrv_root_attach_child(bs, "root", &child_root, blk->ctx,
> blk->perm, blk->shared_perm, blk, errp);
Pavel Dovgalyuk
next prev parent reply other threads:[~2019-09-19 12:12 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-17 11:57 [Qemu-devel] [for-4.2 PATCH 0/6] Block-related record/replay fixes Pavel Dovgalyuk
2019-09-17 11:57 ` [Qemu-devel] [for-4.2 PATCH 1/6] block: implement bdrv_snapshot_goto for blkreplay Pavel Dovgalyuk
2019-09-17 11:57 ` [Qemu-devel] [for-4.2 PATCH 2/6] replay: disable default snapshot for record/replay Pavel Dovgalyuk
2019-09-17 11:58 ` [Qemu-devel] [for-4.2 PATCH 3/6] replay: update docs for record/replay with block devices Pavel Dovgalyuk
2019-09-18 9:18 ` Kevin Wolf
2019-09-18 9:22 ` Pavel Dovgalyuk
2019-09-18 9:33 ` Kevin Wolf
2019-09-18 9:37 ` Pavel Dovgalyuk
2019-09-18 9:44 ` Kevin Wolf
2019-09-18 9:52 ` Pavel Dovgalyuk
2019-09-19 8:53 ` Kevin Wolf
2019-09-19 9:05 ` Pavel Dovgalyuk
2019-09-19 11:27 ` Kevin Wolf
2019-09-19 12:10 ` Pavel Dovgalyuk [this message]
2019-09-19 13:00 ` Kevin Wolf
2019-09-20 7:25 ` Pavel Dovgalyuk
2019-09-20 10:01 ` Kevin Wolf
2019-09-23 6:15 ` Pavel Dovgalyuk
2019-09-25 9:02 ` Pavel Dovgalyuk
2019-10-01 8:22 ` Pavel Dovgalyuk
2019-10-10 15:28 ` Kevin Wolf
2019-10-11 6:10 ` Pavel Dovgalyuk
2019-10-11 9:12 ` Kevin Wolf
2019-10-18 12:06 ` Pavel Dovgalyuk
2019-10-18 14:16 ` Kevin Wolf
2019-09-17 11:58 ` [Qemu-devel] [for-4.2 PATCH 4/6] replay: don't drain/flush bdrv queue while RR is working Pavel Dovgalyuk
2019-09-17 11:58 ` [Qemu-devel] [for-4.2 PATCH 5/6] replay: finish record/replay before closing the disks Pavel Dovgalyuk
2019-09-17 11:58 ` [Qemu-devel] [for-4.2 PATCH 6/6] replay: add BH oneshot event for block layer Pavel Dovgalyuk
2019-09-17 18:09 ` [Qemu-devel] [for-4.2 PATCH 0/6] Block-related record/replay fixes no-reply
2019-09-17 18:10 ` no-reply
2019-09-17 19:01 ` Alex Bennée
2019-09-18 8:26 ` Pavel Dovgalyuk
2019-09-18 10:42 ` Alex Bennée
2019-09-18 11:32 ` Pavel Dovgalyuk
2019-10-11 9:17 ` Kevin Wolf
-- strict thread matches above, loose matches on Subject: below --
2019-07-29 6:29 [Qemu-devel] " Pavel Dovgalyuk
2019-07-29 6:29 ` [Qemu-devel] [for-4.2 PATCH 3/6] replay: update docs for record/replay with block devices Pavel Dovgalyuk
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='001a01d56ee3$4354a530$c9fdef90$@ru' \
--to=dovgaluk@ispras.ru \
--cc=alex.bennee@linaro.org \
--cc=armbru@redhat.com \
--cc=artem.k.pisarenko@gmail.com \
--cc=boost.lists@gmail.com \
--cc=ciro.santilli@gmail.com \
--cc=crosthwaite.peter@gmail.com \
--cc=dgilbert@redhat.com \
--cc=jasowang@redhat.com \
--cc=kraxel@redhat.com \
--cc=kwolf@redhat.com \
--cc=maria.klimushenkova@ispras.ru \
--cc=mreitz@redhat.com \
--cc=mst@redhat.com \
--cc=pavel.dovgaluk@ispras.ru \
--cc=pbonzini@redhat.com \
--cc=peter.maydell@linaro.org \
--cc=qemu-devel@nongnu.org \
--cc=quintela@redhat.com \
--cc=rth@twiddle.net \
--cc=thomas.dullien@googlemail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).