From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1T0QkA-0002Pv-G5 for mharc-qemu-trivial@gnu.org; Sun, 12 Aug 2012 01:29:42 -0400 Received: from eggs.gnu.org ([208.118.235.92]:53884) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T0Qk7-0002HD-K8 for qemu-trivial@nongnu.org; Sun, 12 Aug 2012 01:29:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1T0Qk6-0000vq-Ol for qemu-trivial@nongnu.org; Sun, 12 Aug 2012 01:29:39 -0400 Received: from isrv.corpit.ru ([86.62.121.231]:60508) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T0Qk2-0000vC-6G; Sun, 12 Aug 2012 01:29:34 -0400 Received: from [192.168.88.2] (mjt.vpn.tls.msk.ru [192.168.177.99]) by isrv.corpit.ru (Postfix) with ESMTP id ACF6BA0AB1; Sun, 12 Aug 2012 09:29:21 +0400 (MSK) Message-ID: <50273F30.5080905@msgid.tls.msk.ru> Date: Sun, 12 Aug 2012 09:29:20 +0400 From: Michael Tokarev Organization: Telecom Service, JSC User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:10.0.5) Gecko/20120624 Icedove/10.0.5 MIME-Version: 1.0 To: Peter Maydell References: <1344720275-26744-1-git-send-email-peter.maydell@linaro.org> In-Reply-To: <1344720275-26744-1-git-send-email-peter.maydell@linaro.org> X-Enigmail-Version: 1.4.1 OpenPGP: id=804465C5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 86.62.121.231 Cc: qemu-trivial@nongnu.org, qemu-devel@nongnu.org, patches@linaro.org Subject: Re: [Qemu-trivial] [PATCH] iov_send_recv(): Handle zero bytes case even if OS does not X-BeenThere: qemu-trivial@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 12 Aug 2012 05:29:40 -0000 On 12.08.2012 01:24, Peter Maydell wrote: > POSIX allows sendmsg() and recvmsg() to fail EMSGSIZE if passed a zero > msg.msg_iovlen (in particular the MacOS X implementation will do this). > Handle the case where iov_send_recv() is passed a zero byte count > explicitly, to avoid accidentally depending on the OS to treat zero > msg_iovlen as a no-op. > Signed-off-by: Peter Maydell > --- > This is what was causing 'make check' to fail on MacOS X. > The other option was to declare that a zero bytecount was illegal, I guess. I don't think sending/receiving zero bytes is a good idea in the first place. Which test were failed on MacOS? Was it failing at test-iov "random I/O"? I thought I ensured that the test does not call any i/o function with zero "count" argument. Might be I was wrong, and in that case THAT place should be fixed instead. Can you provide a bit more details please? The whole thing is actually interesting: this is indeed a system- dependent corner case which should be handled in the code to make the routine consistent. But how to fix this is an open question I think. Your approach seems to be best, but we as well may print a warning there... Thank you! /mjt > iov.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/iov.c b/iov.c > index b333061..60705c7 100644 > --- a/iov.c > +++ b/iov.c > @@ -146,6 +146,13 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, > { > ssize_t ret; > unsigned si, ei; /* start and end indexes */ > + if (bytes == 0) { > + /* Catch the do-nothing case early, as otherwise we will pass an > + * empty iovec to sendmsg/recvmsg(), and not all implementations > + * accept this. > + */ > + return 0; > + } > > /* Find the start position, skipping `offset' bytes: > * first, skip all full-sized vector elements, */ From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:53873) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T0Qk4-0002Gl-JC for qemu-devel@nongnu.org; Sun, 12 Aug 2012 01:29:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1T0Qk2-0000vZ-Dl for qemu-devel@nongnu.org; Sun, 12 Aug 2012 01:29:36 -0400 Message-ID: <50273F30.5080905@msgid.tls.msk.ru> Date: Sun, 12 Aug 2012 09:29:20 +0400 From: Michael Tokarev MIME-Version: 1.0 References: <1344720275-26744-1-git-send-email-peter.maydell@linaro.org> In-Reply-To: <1344720275-26744-1-git-send-email-peter.maydell@linaro.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] iov_send_recv(): Handle zero bytes case even if OS does not List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: qemu-trivial@nongnu.org, qemu-devel@nongnu.org, patches@linaro.org On 12.08.2012 01:24, Peter Maydell wrote: > POSIX allows sendmsg() and recvmsg() to fail EMSGSIZE if passed a zero > msg.msg_iovlen (in particular the MacOS X implementation will do this). > Handle the case where iov_send_recv() is passed a zero byte count > explicitly, to avoid accidentally depending on the OS to treat zero > msg_iovlen as a no-op. > Signed-off-by: Peter Maydell > --- > This is what was causing 'make check' to fail on MacOS X. > The other option was to declare that a zero bytecount was illegal, I guess. I don't think sending/receiving zero bytes is a good idea in the first place. Which test were failed on MacOS? Was it failing at test-iov "random I/O"? I thought I ensured that the test does not call any i/o function with zero "count" argument. Might be I was wrong, and in that case THAT place should be fixed instead. Can you provide a bit more details please? The whole thing is actually interesting: this is indeed a system- dependent corner case which should be handled in the code to make the routine consistent. But how to fix this is an open question I think. Your approach seems to be best, but we as well may print a warning there... Thank you! /mjt > iov.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/iov.c b/iov.c > index b333061..60705c7 100644 > --- a/iov.c > +++ b/iov.c > @@ -146,6 +146,13 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, > { > ssize_t ret; > unsigned si, ei; /* start and end indexes */ > + if (bytes == 0) { > + /* Catch the do-nothing case early, as otherwise we will pass an > + * empty iovec to sendmsg/recvmsg(), and not all implementations > + * accept this. > + */ > + return 0; > + } > > /* Find the start position, skipping `offset' bytes: > * first, skip all full-sized vector elements, */