netdev - Re: remove kernel_setsockopt and kernel

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Date:   Thu, 21 May 2020 11:11:50 +0200
From:   'Christoph Hellwig' <hch@....de>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Christoph Hellwig' <hch@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Jon Maloy <jmaloy@...hat.com>,
        Ying Xue <ying.xue@...driver.com>,
        "drbd-dev@...ts.linbit.com" <drbd-dev@...ts.linbit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "linux-afs@...ts.infradead.org" <linux-afs@...ts.infradead.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "cluster-devel@...hat.com" <cluster-devel@...hat.com>,
        "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
        "rds-devel@....oracle.com" <rds-devel@....oracle.com>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>
Subject: Re: remove kernel_setsockopt and kernel_getsockopt v2

On Thu, May 21, 2020 at 08:01:33AM +0000, David Laight wrote:
> How much does this increase the kernel code by?

 44 files changed, 660 insertions(+), 843 deletions(-)


> You are also replicating a lot of code making it more
> difficult to maintain.

No, I specifically don't.

> I don't think the performance of an socket option code
> really matters - it is usually done once when a socket
> is initialised and the other costs of establishing a
> connection will dominate.
> 
> Pulling the user copies outside the [gs]etsocksopt switch
> statement not only reduces the code size (source and object)
> and trivially allows kernel_[sg]sockopt() to me added to
> the list of socket calls.
> 
> It probably isn't possible to pull the usercopies right
> out into the syscall wrapper because of some broken
> requests.

Please read through the previous discussion of the rationale and the
options.  We've been there before.

> I worried about whether getsockopt() should read the entire
> user buffer first. SCTP needs the some of it often (including a
> sockaddr_storage in one case), TCP needs it once.
> However the cost of reading a few words is small, and a big
> buffer probably needs setting to avoid leaking kernel
> memory if the structure has holes or fields that don't get set.
> Reading from userspace solves both issues.

As mention in the thread on the last series:  That was my first idea, but
we have way to many sockopts, especially in obscure protocols that just
hard code the size.  The chance of breaking userspace in a way that can't
be fixed without going back to passing user pointers to get/setsockopt
is way to high to commit to such a change unfortunately.