linux-kernel - Re: [PATCH 0/6] kernel tinification: optionally compile out splice family of syscalls (splice, vmsplice, tee and sendfile)

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Message-ID: <CAMuHMdW8gAiyFiPHu-N4Dg_+b6Qg9JXZZ3PqOn=VmZLcEH-Xkg@mail.gmail.com>
Date:	Mon, 24 Nov 2014 09:38:20 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Pieter Smith <pieter@...sman.nl>,
	David Miller <davem@...emloft.net>,
	alexander.h.duyck@...el.com, Al Viro <viro@...iv.linux.org.uk>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Andrew Morton <akpm@...ux-foundation.org>, beber@...eeweb.net,
	catalina.mocanu@...il.com, Daniel Borkmann <dborkman@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Fabian Frederick <fabf@...net.be>,
	fuse-devel@...ts.sourceforge.net, Hugh Dickins <hughd@...gle.com>,
	iulia.manda21@...il.com, Jan Beulich <JBeulich@...e.com>,
	bfields@...ldses.org, jlayton@...chiereds.net,
	linux-api@...r.kernel.org,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Matt Turner <mattst88@...il.com>, Mel Gorman <mgorman@...e.de>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>, Paul.Durrant@...rix.com,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Peter Foley <pefoley2@...oley.com>,
	Thomas Graf <tgraf@...g.ch>, Tom Herbert <therbert@...gle.com>,
	willemb@...gle.com, xiaoguangrong@...ux.vnet.ibm.com,
	zhenglong.cai@...c.com.cn
Subject: Re: [PATCH 0/6] kernel tinification: optionally compile out splice
 family of syscalls (splice, vmsplice, tee and sendfile)

On Mon, Nov 24, 2014 at 12:36 AM, Josh Triplett <josh@...htriplett.org> wrote:
> On Sun, Nov 23, 2014 at 09:30:40PM +0100, Pieter Smith wrote:
>> On Sun, Nov 23, 2014 at 11:43:26AM -0800, Josh Triplett wrote:
>> > On Sun, Nov 23, 2014 at 01:46:23PM -0500, David Miller wrote:
>> > > Truly removing sendfile/sendpage means that you can't even compile NFS
>> > > into the tree.
>> >
>> > If you mean the in-kernel nfsd (CONFIG_NFSD), that already has a large
>> > stack of "select" and "depends on", both directly and indirectly; adding
>> > a "select SPLICE_SYSCALL" to it seems fine.  (That select does need
>> > adding, though.  Pieter, you need to test-compile more than just
>> > tinyconfig and defconfig.  Try an allyesconfig with *just* splice turned
>> > off, and make sure that compiles.)
>>
>> Did exacly that. Took forever on my hardware, but no problems.
>
> Ah, I see.  Looking more closely at nfsd, it looks like it already has a
> code path for filesystems that don't do splice.  I think, rather than
> making nfsd select SPLICE_SYSCALL, that it would suffice to change the
> "rqstp->rq_splice_ok = true;" in svc_process_common (net/sunrpc/svc.c)
> to:
>
> rqstp->rq_splice_ok = IS_ENABLED(CONFIG_SPLICE_SYSCALL);
>
> Then nfsd should simply *always* fall back to its non-splice support.

Hence I suggest adding to the nfsd help text:

    While nfsd works without SPLICE_SYSCALL, you may want to enable
    SPLICE_SYSCALL for <...> (performance?) reasons.

(Hmm, does Kconfig need a "suggests", cfr. Debian package dependencies?)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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