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Mon, 15 Nov 2021 11:12:08 -0500 X-MC-Unique: 6nmRlTH8ND2fYb4BM3nyXA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C4E4D10247A6; Mon, 15 Nov 2021 16:12:06 +0000 (UTC) Received: from redhat.com (unknown [10.33.37.1]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 47BD619D9F; Mon, 15 Nov 2021 16:11:18 +0000 (UTC) Date: Mon, 15 Nov 2021 16:11:15 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Hanna Reitz Subject: Re: [PATCH v4 00/25] block layer: split block APIs in global state and I/O Message-ID: References: <20211025101735.2060852-1-eesposit@redhat.com> <93821bd8-2ac0-a19e-7029-900e6a6d9be1@redhat.com> MIME-Version: 1.0 In-Reply-To: <93821bd8-2ac0-a19e-7029-900e6a6d9be1@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.7, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Emanuele Giuseppe Esposito , Kevin Wolf , Vladimir Sementsov-Ogievskiy , Eduardo Habkost , qemu-block@nongnu.org, Juan Quintela , qemu-devel@nongnu.org, Eric Blake , Richard Henderson , Markus Armbruster , "Dr. David Alan Gilbert" , Stefan Hajnoczi , Paolo Bonzini , Fam Zheng , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Nov 15, 2021 at 05:03:28PM +0100, Hanna Reitz wrote: > On 25.10.21 12:17, 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 "global state (GS) API", and > > distinguish them from the thread-safe "I/O API". > > > > The aim of this series is to split the relevant block headers in > > global state and I/O sub-headers. > > Despite leaving quite some comments, the series and the split seem > reasonable to me overall.  (This is a pretty big series, after all, so those > “some comments” stack up against a majority of changes that seem OK to me. > :)) > > One thing I noticed while reviewing is that it’s really hard to verify that > no I/O function calls a GS function.  What would be wonderful is some > function marker like coroutine_fn that marks GS functions (or I/O functions) > and that we could then verify the call paths.  But AFAIU we’ve always wanted > precisely that for coroutine_fn and still don’t have it, so this seems like > extremely wishful thinking... :( Even if we don't programmatically verify these rules, it would be a major step forward if we simply adopted a standard naming convention for the APIs that was essentally self-describing. eg block_io_XXX for all I/O stuff and block_state_XXXX for all global state ,and block_common if we have stuff applicable to both use cases. I wouldn't suggest doing it as part of this series, but I think it'd be worthwhile in general for the medium-long term, despite the code churn in updating all usage in the short term. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|