From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755173Ab0EXBnx (ORCPT ); Sun, 23 May 2010 21:43:53 -0400 Received: from mail.parknet.co.jp ([210.171.160.6]:48782 "EHLO mail.parknet.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753628Ab0EXBnv (ORCPT ); Sun, 23 May 2010 21:43:51 -0400 From: OGAWA Hirofumi To: Jens Axboe Cc: mtk.manpages@gmail.com, Andrew Morton , Linus Torvalds , Miklos Szeredi , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch] pipe: add support for shrinking and growing pipes References: <20100522223838.ebca396a.akpm@linux-foundation.org> <20100523070917.GO23411@kernel.dk> <20100523174706.GP23411@kernel.dk> Date: Mon, 24 May 2010 10:43:45 +0900 In-Reply-To: <20100523174706.GP23411@kernel.dk> (Jens Axboe's message of "Sun, 23 May 2010 19:47:06 +0200") Message-ID: <87632e846m.fsf@devron.myhome.or.jp> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jens Axboe writes: >> > We can easily make F_GETPIPE_SZ return bytes, but I don't think passing >> > in bytes to F_SETPIPE_SZ makes a lot of sense. The pipe array must be a >> > power of 2 in pages. So the question is if that makes the API cleaner, >> > passing in number of pages but returning bytes? Or pass in bytes all >> > around, but have F_SETPIPE_SZ round to the nearest multiple of pow2 in >> > pages if need be. Then it would return a size at least what was passed >> > in, or error. I really think "power of 2 in pages" is simply current implementation detail, not detail of pipe API. >> 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)? Thanks. -- OGAWA Hirofumi