From: Sowmini Varadhan <sowmini.varadhan@oracle•com>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: santosh shilimkar <santosh.shilimkar@oracle•com>,
netdev@vger•kernel.org, davem@davemloft•net
Subject: Re: [PATCH v2 net-next] rds-tcp: Add sysctl tunables for sndbuf/rcvbuf on rds-tcp socket
Date: Tue, 15 Mar 2016 14:16:29 -0400 [thread overview]
Message-ID: <20160315181629.GO11063@oracle.com> (raw)
In-Reply-To: <1458065390.31401.45.camel@edumazet-glaptop3.roam.corp.google.com>
On (03/15/16 11:09), Eric Dumazet wrote:
>
> You said "just as user-space SO_SNDBUF allows ridiculous values
> for buffer size.."
>
> So I understood you believe SOCK_MIN_SNDBUF and/or SOCK_MIN_RCVBUF are
> ridiculous ;)
No, no! I was saying that as a clueless user-space app, I can SO_SNDBUF
to 1, and happily think that everything is fine (error == 0), when in
reality the kernel has helpfully fixed up the value for me..
> I pointed to you the actual code.
>
> sk->sk_sndbuf = max_t(u32, val * 2, SOCK_MIN_SNDBUF);
yes, I'm in the process of changing rds-tcp now (doing sanity tests
etc on it, will send out update in a short while)
>
>
> No error is returned. kernel enforces a minimal value.
>
> #define SOCK_MIN_SNDBUF (TCP_SKB_MIN_TRUESIZE * 2)
> #define TCP_SKB_MIN_TRUESIZE (2048 + SKB_DATA_ALIGN(sizeof(struct
> sk_buff)))
>
> -> 2 * (2048 + 256) = 4608 given current sk_buff overhead (that might
> change in linux 5.4 ... )
Yes, I've seen the comments somewhere (in sock_setsockopt?)
it's a bit unexpectd for someone coming from bsd/solaris because
the value returned by getsockopt is quite unpredictable (as you
point out, depends on the kernel version among other things).
> But again if your sysctl allows to set a value below SOCK_MIN_SNDBUF,
> that might be a problem, because stack could have a hidden bug for very
> small values of sndbuf/rcvbuf.
sure, fixing/testing it as I write this.
--Sowmini
next prev parent reply other threads:[~2016-03-15 18:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-15 15:12 [PATCH v2 net-next] rds-tcp: Add sysctl tunables for sndbuf/rcvbuf on rds-tcp socket Sowmini Varadhan
2016-03-15 16:38 ` santosh shilimkar
2016-03-15 16:58 ` Sowmini Varadhan
2016-03-15 17:18 ` Eric Dumazet
2016-03-15 17:30 ` Sowmini Varadhan
2016-03-15 18:09 ` Eric Dumazet
2016-03-15 18:16 ` Sowmini Varadhan [this message]
2016-03-15 17:30 ` Tom Herbert
2016-03-15 17:34 ` Sowmini Varadhan
2016-03-15 17:47 ` Tom Herbert
2016-03-15 19:57 ` Sowmini Varadhan
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