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

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Date:	Mon, 24 May 2010 16:46:03 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Jens Axboe <jens.axboe@...cle.com>
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

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. :)

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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