From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 59A74C3DA64 for ; Wed, 31 Jul 2024 15:34:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sZBLG-0001GR-0f; Wed, 31 Jul 2024 11:34:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZBLE-0001Fx-GK for qemu-devel@nongnu.org; Wed, 31 Jul 2024 11:34:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZBLC-00027J-V8 for qemu-devel@nongnu.org; Wed, 31 Jul 2024 11:34:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722440052; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xt1y7Ymbjhp98Ia+dUFO04kudEZcuVG8h77B37Uxuck=; b=Nx1Xb9nai6DFuaatY+w00aGWY8bRtuckxri+PudPUXdX49tmHu03adLfH4bvMQaRxwGMlJ YH16/B1de/Oa9W6GwfHo7f+gBcgil3Ec8ohmBCRcyQyA8J44eRPuUPCKqILLpSxeVm/pCX DWkwQ7D0p2sn0IRmbqWsrEcEEMfzHCk= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-307-PugLXuxaNGCJUqjN3ezfaA-1; Wed, 31 Jul 2024 11:34:11 -0400 X-MC-Unique: PugLXuxaNGCJUqjN3ezfaA-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0D6DF1955F43; Wed, 31 Jul 2024 15:34:10 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.33]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 21B89300022B; Wed, 31 Jul 2024 15:34:05 +0000 (UTC) Date: Wed, 31 Jul 2024 16:34:01 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Maydell Cc: Philipp Reisner , qemu-devel@nongnu.org, Fabiano Rosas , Peter Xu , Paolo Bonzini , David Hildenbrand Subject: Re: [PATCH] util: retry open() when it gets interrupted by a signal Message-ID: References: <20240731132524.308273-1-philipp.reisner@linbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.126, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Jul 31, 2024 at 04:24:45PM +0100, Peter Maydell wrote: > On Wed, 31 Jul 2024 at 16:21, Daniel P. Berrangé wrote: > > > > On Wed, Jul 31, 2024 at 03:32:52PM +0100, Peter Maydell wrote: > > > This is why we have the RETRY_ON_EINTR() macro, right? > > > > > > Currently we have some places that call qemu_open_old() inside > > > RETRY_ON_EINTR -- we should decide whether we want to > > > handle EINTR inside the qemu_open family of functions, > > > or make the caller deal with it, and put the macro uses > > > in the right place consistently. > > > > It is incredibly arbitrary where we use RETRY_ON_EINTR, which I think > > points towards it being a sub-optimal solution to the general problem. > > Agreed (and agreed that SA_RESTART is the usual approach to > avoid this mess). Partly I just vaguely recall discussions > about this back when we added/improved the RETRY_ON_EINTR > macro in the first place: maybe there's a reason we have it > still... > > > > I agree that it would be nicer if we could use SA_RESTART, > > > but presumably there's a reason why we don't. (At any > > > rate code that's shared with the user-mode emulation > > > has to be EINTR-resistant, because we can't force the > > > user-mode guest code to avoid registering signal handlers > > > that aren't SA_RESTART.) > > > > For user mode emulation isn't it valid to just propagage the > > EINTR back up to the application, since EINTR is a valid errno > > they have to be willing to handle unless the app has itself > > use SA_RESTART. > > Yes, that's what we must do for cases where we are doing some > syscall on behalf of the guest. But for cases where we're > doing a syscall because of something QEMU itself needs to do, > we may need to retry, because we might not be in a position > to be able to back out of what we're doing (or we might not > even be inside the "handle a guest syscall" codepath at all). Ah ok, so RETRY_ON_EINTR conceivably makes sense in the linux-user / bsd-user code in certain scenarios......but it seems almost every single use today is in system emulator code ! With 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 :|