linux-kernel - Re: [patch] pipe: add support for shrinking and growing pipes

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Message-ID: <20100524171522.GT23411@kernel.dk>
Date:	Mon, 24 May 2010 19:15:22 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	mtk.manpages@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] pipe: add support for shrinking and growing pipes

On Mon, May 24 2010, OGAWA Hirofumi wrote:
> Jens Axboe <jens.axboe@...cle.com> writes:
> 
> >> >> I'd recommend this: Pass it in and out in bytes. Don't round to a
> >> >> power of 2. Require the user to know what they are doing. Give an
> >> >> error if the user doesn't supply a power-of-2 * page-size for
> >> >> F_SETPIPE_SZ. (Again, consider the case of architectures  with
> >> >> switchable page sizes.)
> >> >
> >> > But is there much point in erroring on an incorrect size? If the
> >> > application says "I need at least 120kb of space in there", kernel
> >> > returns "OK, you got 128kb". Would returning -1/EINVAL for that case
> >> > really make a better API? Doesn't seem like it to me.
> >> 
> >> FWIW, my first impression of this was setsockopt(SO_RCV/SNDBUF) of unix
> >> socket. Well, API itself wouldn't say "at least this size" or "exactly
> >> this size", so, in here, important thing is consistency of interfaces, I
> >> think. (And the both is sane API at least for me if those had
> >> consistency in the system.)
> >> 
> >> Well, so how about set/get in bytes, and kernel will set "at least
> >> specified size" actually like setsockopt(SO_RCV/SNDBUF)?
> >
> > Isn't that pretty much what I described?
> 
> Yes, probably. Well, 120kb was still multiple of page size. :)

It is, but 120KB/page_size is not (which is the power-of-2 of interest
here).

-- 
Jens Axboe

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