Re: [RFC PATCH] test-bdrv-drain: keep graph manipulations out of coroutines

[Kevin Wolf <kwolf@redhat.com>]

Am 02.12.2022 um 18:22 hat Paolo Bonzini geschrieben:
> On 12/2/22 14:42, Emanuele Giuseppe Esposito wrote:
> > 
> > 
> > Am 02/12/2022 um 14:27 schrieb Paolo Bonzini:
> > > Changes to the BlockDriverState graph will have to take the
> > > corresponding lock for writing, and therefore cannot be done
> > > inside a coroutine.  Move them outside the test body.
> > > 
> > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > > ---
> > >   tests/unit/test-bdrv-drain.c | 63 ++++++++++++++++++++++++++----------
> > >   1 file changed, 46 insertions(+), 17 deletions(-)
> > > 
> > > diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
> > > index 6ae44116fe79..d85083dd4f9e 100644
> > > --- a/tests/unit/test-bdrv-drain.c
> > > +++ b/tests/unit/test-bdrv-drain.c
> > > @@ -199,25 +199,40 @@ static void do_drain_end_unlocked(enum drain_type drain_type, BlockDriverState *
> > >       }
> > >   }
> > > +static BlockBackend *blk;
> > > +static BlockDriverState *bs, *backing;
> > > +
> > > +static void test_drv_cb_init(void)
> > > +{
> > > +    blk = blk_new(qemu_get_aio_context(), BLK_PERM_ALL, BLK_PERM_ALL);
> > > +    bs = bdrv_new_open_driver(&bdrv_test, "test-node", BDRV_O_RDWR,
> > > +                              &error_abort);
> > > +    blk_insert_bs(blk, bs, &error_abort);
> > > +
> > > +    backing = bdrv_new_open_driver(&bdrv_test, "backing", 0, &error_abort);
> > > +    bdrv_set_backing_hd(bs, backing, &error_abort);
> > > +}
> > > +
> > > +static void test_drv_cb_fini(void)
> > 
> > fini stands for "finito"? :)
> 
> No, for finish :)
> http://ftp.math.utah.edu/u/ma/hohn/linux/misc/elf/node3.html
> 
> > Anyways, an alternative solution for this is also here (probably coming
> > from you too):
> > https://lists.nongnu.org/archive/html/qemu-devel/2022-03/msg03517.html
> 
> Much better.  At least patches 7-8 from that series have to be salvaged,
> possibly 10 as well.

I wonder if we need a more general solution for this because this test
is not the only place that calls this kind of functions in a coroutine.
The one I'm aware of in particular is all the .bdrv_co_create
implementations, but I'm almost sure there are more.

Can we use a yield_to_drain()-like mechanism for these functions? Maybe
even something like the opposite of co_wrapper, a no_co_wrapper that
generates a foo_co() variant that drops out of coroutine context before
calling foo()?

Kevin