Messages in this thread | | | Date | Fri, 26 Mar 2010 15:54:40 -0700 | Subject | Re: [PATCH 0/4] io-controller: Use names rather than major:minor | From | Chad Talbott <> |
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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.
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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