From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xin Long Subject: Re: send/sendmsg ENOMEM errors WAS(Re: [PATCH net 6/6] sctp: not return ENOMEM err back in sctp_packet_transmit Date: Mon, 24 Oct 2016 14:30:07 +0800 Message-ID: References: <2fa21505-59c2-fb8b-6e89-11fccc953d25@mojatatu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: "netdev@vger.kernel.org" , Marcelo Ricardo Leitner , Vlad Yasevich , Daniel Borkmann , David Miller , "linux-sctp@vger.kernel.org" , Michael Tuexen , Eric Dumazet , Brenda Butler , gabor@mojatatu.com To: Jamal Hadi Salim Return-path: Received: from mail-qk0-f193.google.com ([209.85.220.193]:36217 "EHLO mail-qk0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754938AbcJXGaI (ORCPT ); Mon, 24 Oct 2016 02:30:08 -0400 In-Reply-To: <2fa21505-59c2-fb8b-6e89-11fccc953d25@mojatatu.com> Sender: netdev-owner@vger.kernel.org List-ID: [1] >> This patch doesn't ignore all the ENOMEN cases, only after msg is >> enqueued in out queue/send queue, in the lower layer, when alloc >> new skb and copy data from old skb, if it fails to alloc new skb, sctp >> will ignore this ENOMEM, as this msg will be taken care by retransmit >> mechanism, it's reasonable and also safe, user can't feel that. >> > > Yes, that part i got. > [2] >> But for the cases before enqueue, like in sctp_sendmsg, >> sctp_datamsg_from_user may return ENOMEM, this err will return >> back to user, and can't be ignored. >> > > The hard part is distinguishing between the above case and real > failure. > I am assuming in the case above user is _not_ required to send > again. But in the general case they are required to send again. > Correct? in case [1], user can't see the ENOMEM, ENOMEM is more like a internal err. in case [2], user will got the ENOMEM, they should resend this msg, It's the the general case mentioned-above > >> So I don't really think we should change something in manpage, what >> do you think ? maybe a little explanation there is also nice, :) > > > Yes, that would help. In particular it should be clear what user space > is expected to do. While this is about sctp - I am assuming equivalent > behavior for all callers of sendxxx() regardless of protocol. here sctp's behavior is actually same with tcp's, in tcp, tcp_transmit_skb also may fail to alloc skb, but it doesn't return any err to user, just like sctp_packet_transmit. That's why I don't think we should change something in manpage, as here sctp is consistent with tcp now. make sense ? From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xin Long Date: Mon, 24 Oct 2016 06:30:07 +0000 Subject: Re: send/sendmsg ENOMEM errors WAS(Re: [PATCH net 6/6] sctp: not return ENOMEM err back in sctp_pack Message-Id: List-Id: References: <2fa21505-59c2-fb8b-6e89-11fccc953d25@mojatatu.com> In-Reply-To: <2fa21505-59c2-fb8b-6e89-11fccc953d25@mojatatu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jamal Hadi Salim Cc: "netdev@vger.kernel.org" , Marcelo Ricardo Leitner , Vlad Yasevich , Daniel Borkmann , David Miller , "linux-sctp@vger.kernel.org" , Michael Tuexen , Eric Dumazet , Brenda Butler , gabor@mojatatu.com [1] >> This patch doesn't ignore all the ENOMEN cases, only after msg is >> enqueued in out queue/send queue, in the lower layer, when alloc >> new skb and copy data from old skb, if it fails to alloc new skb, sctp >> will ignore this ENOMEM, as this msg will be taken care by retransmit >> mechanism, it's reasonable and also safe, user can't feel that. >> > > Yes, that part i got. > [2] >> But for the cases before enqueue, like in sctp_sendmsg, >> sctp_datamsg_from_user may return ENOMEM, this err will return >> back to user, and can't be ignored. >> > > The hard part is distinguishing between the above case and real > failure. > I am assuming in the case above user is _not_ required to send > again. But in the general case they are required to send again. > Correct? in case [1], user can't see the ENOMEM, ENOMEM is more like a internal err. in case [2], user will got the ENOMEM, they should resend this msg, It's the the general case mentioned-above > >> So I don't really think we should change something in manpage, what >> do you think ? maybe a little explanation there is also nice, :) > > > Yes, that would help. In particular it should be clear what user space > is expected to do. While this is about sctp - I am assuming equivalent > behavior for all callers of sendxxx() regardless of protocol. here sctp's behavior is actually same with tcp's, in tcp, tcp_transmit_skb also may fail to alloc skb, but it doesn't return any err to user, just like sctp_packet_transmit. That's why I don't think we should change something in manpage, as here sctp is consistent with tcp now. make sense ?