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 4C2B6E732C0 for ; Thu, 28 Sep 2023 11:11:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qlouW-0003uC-4A; Thu, 28 Sep 2023 07:10:24 -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 1qlouU-0003tw-TA for qemu-devel@nongnu.org; Thu, 28 Sep 2023 07:10:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qlouM-0002j9-7n for qemu-devel@nongnu.org; Thu, 28 Sep 2023 07:10:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695899412; 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=duG3wt3YWGdN1zdnu/+NhHtAW+gOF9wsOXJe8yyRtgk=; b=IlTJbGXwwVL64J39aTEbBxtuOmrbey3bJeiQeo3SisXnLaDXP4d+aQ6X+j8l4tNDVLSqT7 raO6RcGfa5/h4NYmr3AeM/0x/04wY41Jb7FwbxXOScy7ayc+NsSB7iGFXh6ysulonThmw5 6N0yZvq5dP/KptGL13ZQIwWK0kGxbKM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-74-DHv68AEbOg6_OaaEeVXmTg-1; Thu, 28 Sep 2023 07:10:08 -0400 X-MC-Unique: DHv68AEbOg6_OaaEeVXmTg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 627DC85A5BF; Thu, 28 Sep 2023 11:10:08 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.58]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 61A9640C2064; Thu, 28 Sep 2023 11:10:07 +0000 (UTC) Date: Thu, 28 Sep 2023 12:10:04 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Cc: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , qemu-devel@nongnu.org, Paolo Bonzini , Marc Hartmayer Subject: Re: [PATCH] chardev/char-pty: Avoid losing bytes when the other side just (re-)connected Message-ID: References: <20230816210743.1319018-1-thuth@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230816210743.1319018-1-thuth@redhat.com> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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, Aug 16, 2023 at 11:07:43PM +0200, Thomas Huth wrote: > When starting a guest via libvirt with "virsh start --console ...", > the first second of the console output is missing. This is especially > annoying on s390x that only has a text console by default and no graphical > output - if the bios fails to boot here, the information about what went > wrong is completely lost. > > One part of the problem (there is also some things to be done on the > libvirt side) is that QEMU only checks with a 1 second timer whether > the other side of the pty is already connected, so the first second of > the console output is always lost. > > This likely used to work better in the past, since the code once checked > for a re-connection during write, but this has been removed in commit > f8278c7d74 ("char-pty: remove the check for connection on write") to avoid > some locking. > > To ease the situation here at least a little bit, let's check with g_poll() > whether we could send out the data anyway, even if the connection has not > been marked as "connected" yet. The file descriptor is marked as non-blocking > anyway since commit fac6688a18 ("Do not hang on full PTY"), so this should > not cause any trouble if the other side is not ready for receiving yet. > > With this patch applied, I can now successfully see the bios output of > a s390x guest when running it with "virsh start --console" (with a patched > version of virsh that fixes the remaining issues there, too). > > Reported-by: Marc Hartmayer > Signed-off-by: Thomas Huth > --- > chardev/char-pty.c | 22 +++++++++++++++++++--- > 1 file changed, 19 insertions(+), 3 deletions(-) Reviewed-by: Daniel P. Berrangé 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 :|