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

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Date:	Sun, 23 Nov 2014 19:28:10 -0500
From:	Jeff Layton <jlayton@...chiereds.net>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Pieter Smith <pieter@...sman.nl>,
	David Miller <davem@...emloft.net>,
	alexander.h.duyck@...el.com, viro@...iv.linux.org.uk,
	ast@...mgrid.com, akpm@...ux-foundation.org, beber@...eeweb.net,
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	edumazet@...gle.com, ebiederm@...ssion.com, fabf@...net.be,
	fuse-devel@...ts.sourceforge.net, geert@...ux-m68k.org,
	hughd@...gle.com, iulia.manda21@...il.com, JBeulich@...e.com,
	bfields@...ldses.org, linux-api@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
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	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 Sun, 23 Nov 2014 15:36:37 -0800
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.
> 

I'd probably prefer the above, actually. We have to keep supporting
non-splice enabled fs' for the forseeable future, so we may as well
allow people to run nfsd in such configurations. It could even be
useful for testing the non-splice-enabled codepaths.

> That said, given that it seems exceedingly unlikely that anyone would
> use the in-kernel nfsd on a system trying to minimize kernel size, it
> still seems cleaner to just "select SPLICE_SYSCALL" from NFSD in
> Kconfig.  That avoids making any changes at all to the nfsd source in
> this patch series.
> 

-- 
Jeff Layton <jlayton@...chiereds.net>
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