From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [patch] pipe: add support for shrinking and growing pipes Date: Mon, 24 May 2010 09:05:52 +0200 Message-ID: <20100524070552.GR23411@kernel.dk> References: <20100522223838.ebca396a.akpm@linux-foundation.org> <20100523070917.GO23411@kernel.dk> <20100523174706.GP23411@kernel.dk> <87632e846m.fsf@devron.myhome.or.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: OGAWA Hirofumi , Andrew Morton , Linus Torvalds , Miklos Szeredi , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: mtk.manpages@gmail.com Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org > The "at least" idea makes sense. So, I'd change my recommendation to: > > Pass the buffer size in and out in bytes (for consistency with other > APIs). Round the input (F_SETPIPE_SZ) value up as required by the > implementation. For the output (F_GETPIPE_SZ) value do one of the > following: > a) Return the value given on input. > b) Return the rounded up value actually used by the kernel. > > I suspect (b) might be more useful: if an application cares enough > about pipe size to want to change it, then at least some such > applications might care to know exactly the size that the kernel used. > (And: I can't see any downside to (b).) b definitely, since it's the real size (plus then we don't have to track the passed in size). > One other comment about the interface. We have > > if (!capable(CAP_SYS_ADMIN) && arg > pipe_max_pages) > return -EINVAL; > > The usual error on a capability denied is EPERM. Please change. Right, that looks like a thinko. I'll submit a patch changing it to bytes and the agreed API and fix this -Eerror. Thanks for your comments and suggestions! -- Jens Axboe