netdev - Re: send/sendmsg ENOMEM errors WAS(Re: [PATCH net 6/6] sctp: not return ENOMEM err back in sctp_packet

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Date:   Tue, 25 Oct 2016 17:05:41 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Vlad Yasevich <vyasevic@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        Michael Tuexen <Michael.Tuexen@...chi.franken.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Brenda Butler <bjb@...atatu.com>, gabor@...atatu.com
Subject: Re: send/sendmsg ENOMEM errors WAS(Re: [PATCH net 6/6] sctp: not
 return ENOMEM err back in sctp_packet_transmit

>> in case [1], user can't see the ENOMEM, ENOMEM is more like
>> a internal err.
>>
>
> Still not clear. Are you saying, say an old kernel like 3.11 would
> not return the user ENOMEN for the use case[1] you fixed? I am not
> talking post your fix.
Sorry for confusing you.

3.11 would return the user ENOMEN for the use case[1].
but this behavior is incorrect, it's not consistent with tcp.

>
>> in case [2], user will got the ENOMEM, they should resend this msg,
>> It's the the general case mentioned-above
>>
>
> I am trying to see if we can avoid backporting this fix to 3.11.
> In [1], is ENOMEM propagated to user space (dont talk about your
> fix, I mean pre-your-fix).
yes, in [1], pre-my-fix, ENOMEM is propagated to user space.

>
>
>> 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 ?
>
>
> No ;-> The manpage is bad. Go look at it. In the case of ENOBUFS or
> EMSGSIZE it is clear what needs to be done.
> If the answer is _on ENOMEM_ user must resend then thats what we need
> to say.
yes, on ENOMEM user must resend if he want send out this msg successfully.