Messages in this thread | | | From | Divyesh Shah <> | Date | Fri, 26 Mar 2010 16:21:41 -0700 | Subject | Re: [PATCH 0/4] io-controller: Use names rather than major:minor |
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On Fri, Mar 26, 2010 at 3:54 PM, Chad Talbott <ctalbott@google.com> wrote: > On Fri, Mar 26, 2010 at 8:20 AM, Vivek Goyal <vgoyal@redhat.com> 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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