From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752688Ab0CZXWK (ORCPT ); Fri, 26 Mar 2010 19:22:10 -0400 Received: from smtp-out.google.com ([216.239.44.51]:37530 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751895Ab0CZXWI convert rfc822-to-8bit (ORCPT ); Fri, 26 Mar 2010 19:22:08 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:from:date:message-id: subject:to:cc:content-type:content-transfer-encoding:x-system-of-record; b=o714SYr+hCSC4O1SCb5WsUwXRJsPSG05ofA0Nm9pMI7a/+Iu4ud8WF8EQbso9jhd0 wsaL4YAWeW1C36M2X3eGg== MIME-Version: 1.0 In-Reply-To: <1786ab031003261554y40c21bc8sb4ea2f347c2c8bf8@mail.gmail.com> References: <20100325180310.25299.64877.stgit@meat.mtv.corp.google.com> <4BAC0E7D.9080305@cn.fujitsu.com> <20100326152012.GB18128@redhat.com> <1786ab031003261554y40c21bc8sb4ea2f347c2c8bf8@mail.gmail.com> From: Divyesh Shah Date: Fri, 26 Mar 2010 16:21:41 -0700 Message-ID: Subject: Re: [PATCH 0/4] io-controller: Use names rather than major:minor To: Chad Talbott Cc: Vivek Goyal , Gui Jianfeng , jens.axboe@oracle.com, mrubin@google.com, Li Zefan , linux-kernel@vger.kernel.org, Nauman Rafique Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 26, 2010 at 3:54 PM, Chad Talbott wrote: > On Fri, Mar 26, 2010 at 8:20 AM, Vivek Goyal wrote: >> On Fri, Mar 26, 2010 at 09:31:41AM +0800, Gui Jianfeng wrote: >>> +int blk_lookup_devname(dev_t devt, char *name) >>> +{ > > [ snip... loop through all block devices for devt ...snip ] > >>> So we can keep dev_t in blkio layer, and export to user a device name by calling >>> this function. Also, we retrive device number by calling blk_lookup_devt(). >>> This change might keep things much simple. Jens, do you have any thoughts? >>> >> I agree with Gui that lets keep the dev_t the core in blkio layer. Keeping >> a pointer to gendisk in request queue is becoming little messy. > > Agreed on leaving gendisk pointer out of request_queue.  In doing > further investigation, I've found that it's up to the driver to > maintain the association between gendisk and request_queue, and some > drivers put multiple gendisk behind a single request_queue, so the > back pointer would be ill-specified. > >> But if that does not work for you, then I would also like to keep things >> simple and translate dev_t to diskname during read routine. Similiarly, >> while somebody is putting policy, use blk_lookup_devt(). > > I like the simplicity of blk_lookup_devt(), but I don't like the idea > of iterating through all block devices on every lookup of the name. > Perhaps we could cache the name somewhere? > > Actually, the name is the name of the *queue* (or the key in > blk-cgroup), because as I mentioned above there can be a many to one > relationship between disks and queues in general. > > The more I think about it, the more it seems to make sense to extend > blkio_policy_ops to include a function to get the name of the key. > blk-cgroup makes no current use of the dev, except to invent a name > for the request_queue whose policy is being set or printed.  It could > be argued that the thing being scheduled has a better idea of the name > of that thing. > >> But this will lead to issue of how do you now display both device number >> and disk name in the output. May be following. >> >> major:minor  diskname  data >> >> I am not sure if people are fond of multiple values in a single file. At >> the same time for setting the rules or deleting the rules, it will make >> syntax complicated/confusing. Also will require breaking ABI for existing >> blkio.time, blkio.sectors, blkio.dequeue files. > > I don't like this, either.  It breaks ABI and is more confusing for users. > >> So I would prefer to keep the major/minor number based interface for >> follwing reasons. >> >> - Chaning it now breaks ABI. >> - Other cgroup controller "device" is also using major/minor number based >>  interface for device access policy. So it is consistent with other >>  controller. > > Which controllers are these? > >> - Displaying both device major/minor and diskname is an option but that >>  makes the file format syntax little complicated and new rule setting >>  or removoal confusing. > > A few messages back you mentioned that you preferred device names > because they would be better for users of the system.  If there was a > simple implementation, would you still be behind a new name-based > interface?  We could go that direction and maintain ABI by deprecating > current interface and making a new interface with names. > > If you can't tell, I'm a big fan of using the name! :)  It's *much* > more consistent with the interfaces in /sys. I agree with Chad here. The major/minor number interface to me seems like a departure from convention as /proc/diskstat, /sys/block all use the device names at the kernel-user interface. About deprecating the current ABI, we could do that but do we expect a lot of user tools to be built around this interface since the 2.6.33 release already? -Divyesh > > Chad >