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

[Geert Uytterhoeven]

On Mon, Nov 24, 2014 at 12:36 AM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx

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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