From: Stefan Hajnoczi <stefanha@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Emanuele Giuseppe Esposito" <eesposit@redhat.com>,
"Kevin Wolf" <kwolf@redhat.com>,
"Vladimir Sementsov-Ogievskiy" <vsementsov@virtuozzo.com>,
"Daniel P. Berrangé" <berrange@redhat.com>,
"Eduardo Habkost" <ehabkost@redhat.com>,
qemu-block@nongnu.org, "Juan Quintela" <quintela@redhat.com>,
"John Snow" <jsnow@redhat.com>,
"Richard Henderson" <richard.henderson@linaro.org>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
qemu-devel@nongnu.org, "Hanna Reitz" <hreitz@redhat.com>,
"Fam Zheng" <fam@euphon.net>, "Eric Blake" <eblake@redhat.com>
Subject: Re: [RFC PATCH 0/4] block layer: split block APIs in graph and I/O
Date: Wed, 15 Sep 2021 15:43:35 +0100 [thread overview]
Message-ID: <YUIGlyfL+SleHCAc@stefanha-x1.localdomain> (raw)
In-Reply-To: <916c8456-9433-42a0-df2d-3e62ced283fd@redhat.com>
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On Wed, Sep 15, 2021 at 02:11:41PM +0200, Paolo Bonzini wrote:
> On 13/09/21 15:10, Stefan Hajnoczi wrote:
> > On Wed, Sep 08, 2021 at 09:10:17AM -0400, Emanuele Giuseppe Esposito wrote:
> > > Currently, block layer APIs like block-backend.h contain a mix of
> > > functions that are either running in the main loop and under the
> > > BQL, or are thread-safe functions and run in iothreads performing I/O.
> > > The functions running under BQL also take care of modifying the
> > > block graph, by using drain and/or aio_context_acquire/release.
> > > This makes it very confusing to understand where each function
> > > runs, and what assumptions it provided with regards to thread
> > > safety.
> > >
> > > We call the functions running under BQL "graph API", and
> > > distinguish them from the thread-safe "I/O API".
> >
> > Maybe "BQL" is clearer than "graph" because not all functions classified
> > as "graph" need to traverse/modify the graph.
>
> Bikeshedding, I like it! :)
>
> ... on the other hand, qemu-storage-daemon does not have a BQL (see patch
> 1); "graph API" functions run from the main (monitor) thread.
>
> The characteristic of the "graph API" is that they affect global state, so
> another possibility could be "global state API". But is there any global
> state apart from the BlockDriverState graph and the associated
> BlockBackends?
I would be happy with that name too.
Stefan
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next prev parent reply other threads:[~2021-09-15 14:44 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-08 13:10 [RFC PATCH 0/4] block layer: split block APIs in graph and I/O Emanuele Giuseppe Esposito
2021-09-08 13:10 ` [RFC PATCH 1/4] main-loop.h: introduce qemu_in_main_thread() Emanuele Giuseppe Esposito
2021-09-13 13:15 ` Stefan Hajnoczi
2021-09-08 13:10 ` [RFC PATCH 2/4] migration: block-dirty-bitmap: add missing qemu_mutex_lock_iothread Emanuele Giuseppe Esposito
2021-09-13 13:19 ` Stefan Hajnoczi
2021-09-08 13:10 ` [RFC PATCH 3/4] include/sysemu/block-backend: split header into I/O and graph API Emanuele Giuseppe Esposito
2021-09-13 13:27 ` Stefan Hajnoczi
2021-09-15 12:14 ` Paolo Bonzini
2021-09-15 14:38 ` Stefan Hajnoczi
2021-09-13 13:41 ` Stefan Hajnoczi
2021-09-08 13:10 ` [RFC PATCH 4/4] block/block-backend.c: assertions for block-backend Emanuele Giuseppe Esposito
2021-09-13 13:38 ` Stefan Hajnoczi
2021-09-13 13:10 ` [RFC PATCH 0/4] block layer: split block APIs in graph and I/O Stefan Hajnoczi
2021-09-15 12:11 ` Paolo Bonzini
2021-09-15 14:43 ` Stefan Hajnoczi [this message]
2021-09-16 14:03 ` Emanuele Giuseppe Esposito
2021-09-16 19:49 ` Paolo Bonzini
2021-09-13 13:39 ` Stefan Hajnoczi
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