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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Message-ID: <369b7b2c-d1fb-5dd2-30b9-4f54400aa770@mojatatu.com>
Date:   Mon, 24 Oct 2016 08:38:45 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Xin Long <lucien.xin@...il.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

On 16-10-24 02:30 AM, Xin Long wrote:

> 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.

> 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).


> 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.

cheers,
jamal