netdev - Re: [PATCH 31/33] sctp: add sctp_sock_set

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Date:   Thu, 21 May 2020 10:33:48 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     David Miller <davem@...emloft.net>, kuba@...nel.org,
        edumazet@...gle.com, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        vyasevich@...il.com, nhorman@...driver.com, jmaloy@...hat.com,
        ying.xue@...driver.com, drbd-dev@...ts.linbit.com,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-nvme@...ts.infradead.org, target-devel@...r.kernel.org,
        linux-afs@...ts.infradead.org, linux-cifs@...r.kernel.org,
        cluster-devel@...hat.com, ocfs2-devel@....oracle.com,
        netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        ceph-devel@...r.kernel.org, rds-devel@....oracle.com,
        linux-nfs@...r.kernel.org
Subject: Re: [PATCH 31/33] sctp: add sctp_sock_set_nodelay

On Thu, May 21, 2020 at 10:34:42AM +0200, Christoph Hellwig wrote:
> On Wed, May 20, 2020 at 08:39:13PM -0300, Marcelo Ricardo Leitner wrote:
> > On Wed, May 20, 2020 at 04:23:55PM -0700, David Miller wrote:
> > > From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> > > Date: Wed, 20 May 2020 20:10:01 -0300
> > > 
> > > > The duplication with sctp_setsockopt_nodelay() is quite silly/bad.
> > > > Also, why have the 'true' hardcoded? It's what dlm uses, yes, but the
> > > > API could be a bit more complete than that.
> > > 
> > > The APIs are being designed based upon what in-tree users actually
> > > make use of.  We can expand things later if necessary.
> > 
> > Sometimes expanding things later can be though, thus why the worry.
> > But ok, I get it. Thanks.
> > 
> > The comment still applies, though. (re the duplication)
> 
> Where do you see duplication?
> 
> sctp_setsockopt_nodelay does the following things:
> 
>  - verifies optlen, returns -EINVAL if it doesn't match
>  - calls get_user, returns -EFAULT on error
>  - converts the value from get_user to a boolean and assigns it
>    to sctp_sk(sk)->nodelay
>  - returns 0.
> 
> sctp_sock_set_nodelay does:
> 
>  - call lock_sock
>  - assign true to sctp_sk(sk)->nodelay
>  - call release_sock
>  - does not return an error code

With the patch there are now two ways of enabling nodelay. It may be
just a boolean set today, but if one wants to probe on it or if we
want to extend it with anything, say a debug msg, we have to do it in
two (very different) places.