From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1cakFP-00030t-Tv for mharc-qemu-trivial@gnu.org; Mon, 06 Feb 2017 09:26:27 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43767) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cakFN-0002ym-LK for qemu-trivial@nongnu.org; Mon, 06 Feb 2017 09:26:26 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cakFM-0005lj-R5 for qemu-trivial@nongnu.org; Mon, 06 Feb 2017 09:26:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40142) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cakF6-0005iQ-1O; Mon, 06 Feb 2017 09:26:08 -0500 Received: from smtp.corp.redhat.com (int-mx16.intmail.prod.int.phx2.redhat.com [10.5.11.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 33A433B714; Mon, 6 Feb 2017 14:26:08 +0000 (UTC) Received: from nilsson.home.kraxel.org (ovpn-116-97.ams2.redhat.com [10.36.116.97]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1E5B174A13; Mon, 6 Feb 2017 14:26:06 +0000 (UTC) Received: by nilsson.home.kraxel.org (Postfix, from userid 500) id 0E28D8088D; Mon, 6 Feb 2017 15:26:04 +0100 (CET) Message-ID: <1486391163.32329.24.camel@redhat.com> From: Gerd Hoffmann To: Michael Tokarev Cc: qemu-devel@nongnu.org, qemu-trivial@nongnu.org, "Daniel P. Berrange" , qemu-stable@nongnu.org Date: Mon, 06 Feb 2017 15:26:03 +0100 In-Reply-To: <1486115549-9398-1-git-send-email-mjt@msgid.tls.msk.ru> References: <1486115549-9398-1-git-send-email-mjt@msgid.tls.msk.ru> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 X-Scanned-By: MIMEDefang 2.74 on 10.5.11.28 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Mon, 06 Feb 2017 14:26:08 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-trivial] [PATCH v2] vnc: do not disconnect on EAGAIN X-BeenThere: qemu-trivial@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 06 Feb 2017 14:26:26 -0000 On Fr, 2017-02-03 at 12:52 +0300, Michael Tokarev wrote: > When qemu vnc server is trying to send large update to clients, > there might be a situation when system responds with something > like EAGAIN, indicating that there's no system memory to send > that much data (depending on the network speed, client and server > and what is happening). In this case, something like this happens > on qemu side (from strace): >=20 > sendmsg(16, {msg_name(0)=3DNULL, > msg_iov(1)=3D[{"\244\"..., 729186}], > msg_controllen=3D0, msg_flags=3D0}, 0) =3D 103950 > sendmsg(16, {msg_name(0)=3DNULL, > msg_iov(1)=3D[{"lz\346"..., 1559618}], > msg_controllen=3D0, msg_flags=3D0}, 0) =3D -1 EAGAIN > sendmsg(-1, {msg_name(0)=3DNULL, > msg_iov(1)=3D[{"lz\346"..., 1559618}], > msg_controllen=3D0, msg_flags=3D0}, 0) =3D -1 EBADF >=20 > qemu closes the socket before the retry, and obviously it gets EBADF > when trying to send to -1. >=20 > This is because there WAS a special handling for EAGAIN, but now it doesn= 't > work anymore, after commit 04d2529da27db512dcbd5e99d0e26d333f16efcc, beca= use > now in all error-like cases we initiate vnc disconnect. >=20 > This change were introduced in qemu 2.6, and caused numerous grief for ma= ny > people, resulting in their vnc clients reporting sporadic random disconne= cts > from vnc server. >=20 > Fix that by doing the disconnect only when necessary, i.e. omitting this > very case of EAGAIN. >=20 > Hopefully the existing condition (comparing with QIO_CHANNEL_ERR_BLOCK) > is sufficient, as the original code (before the above commit) were > checking for other errno values too. >=20 > Apparently there's another (semi?)bug exist somewhere here, since the > code tries to write to fd# -1, it probably should check if the connection > is open before. But this isn't important. >=20 > Signed-off-by: Michael Tokarev > Fixes: 04d2529da27db512dcbd5e99d0e26d333f16efcc > Cc: Daniel P. Berrange > Cc: Gerd Hoffmann > Cc: qemu-stable@nongnu.org Added to ui patch queue. thanks, Gerd