Re: [PATCH v2 1/3] block/commit: implement final flush

[Kevin Wolf <kwolf@redhat.com>]

Am 19.07.2024 um 12:35 hat Vladimir Sementsov-Ogievskiy geschrieben:
> On 18.07.24 22:22, Kevin Wolf wrote:
> > Am 26.06.2024 um 16:50 hat Vladimir Sementsov-Ogievskiy geschrieben:
> > > Actually block job is not completed without the final flush. It's
> > > rather unexpected to have broken target when job was successfully
> > > completed long ago and now we fail to flush or process just
> > > crashed/killed.
> > > 
> > > Mirror job already has mirror_flush() for this. So, it's OK.
> > > 
> > > Do this for commit job too.
> > > 
> > > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> > > ---
> > >   block/commit.c | 41 +++++++++++++++++++++++++++--------------
> > >   1 file changed, 27 insertions(+), 14 deletions(-)
> > > 
> > > diff --git a/block/commit.c b/block/commit.c
> > > index 7c3fdcb0ca..81971692a2 100644
> > > --- a/block/commit.c
> > > +++ b/block/commit.c
> > > @@ -134,6 +134,7 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
> > >       int64_t n = 0; /* bytes */
> > >       QEMU_AUTO_VFREE void *buf = NULL;
> > >       int64_t len, base_len;
> > > +    bool need_final_flush = true;
> > >       len = blk_co_getlength(s->top);
> > >       if (len < 0) {
> > > @@ -155,8 +156,8 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
> > >       buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
> > > -    for (offset = 0; offset < len; offset += n) {
> > > -        bool copy;
> > > +    for (offset = 0; offset < len || need_final_flush; offset += n) {
> > 
> > In general, the control flow would be nicer to read if the final flush
> > weren't integrated into the loop, but just added after it.
> > 
> > But I assume this is pretty much required for pausing the job during
> > error handling in the final flush if you don't want to duplicate a lot
> > of the logic into a second loop?
> 
> Right, that's the reason.

This would probably be the right solution if it affected only commit.
But I've thought a bit more about this and given that the same thing
happens in all of the block jobs, I'm really wondering if introducing a
block job helper function wouldn't be better, so that each block job
could just add something like this after its main loop:

    do {
        ret = blk_co_flush();
    } while (block_job_handle_error(job, ret));

And the helper would call block_job_error_action(), stop the job if
necessary, check if it's cancelled, include a pause point etc.

Kevin