Re: [PATCH 0/4] io-controller: Use names rather than major:minor

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Chad Talbott wrote:
> This stack (which includes Gui's patch for per-device weights),
> changes the various blkio.* stats to use the disks' names (sda, sdb,
> etc.) rather than major:minor pairs when printing statistics.

Hi Chad,

I have the same concern with Vivek. We'v already exported device number
pair to user since 2.6.33, It's better to keep the original ABI.

> Additionally setting a per-device policy can be done via the disk's
> name.

To keep things simple, can we add new API in block layer to lookup
device name by device number as following.

+int blk_lookup_devname(dev_t devt, char *name)
+{
+       struct class_dev_iter iter;
+       struct device *dev;
+       struct gendisk *disk;
+
+       class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
+       while ((dev = class_dev_iter_next(&iter))) {
+               if (dev->devt != devt)
+                       continue;
+
+               disk = dev_to_disk(dev);
+
+               disk_name(disk, 0, name);
+
+               return 0;
+       }
+       class_dev_iter_exit(&iter);
+
+       return 1;
+}
+EXPORT_SYMBOL(blk_lookup_devname);
+

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?

Thanks,
Gui

> 
> This has the side effect of fixing the "root cgroup shows no stats"
> problem that Ricky mentioned.
> 
> Chad
> 
> ---
> 
> Chad Talbott (4):
>       blkio_group key change: void * -> request_queue *
>       Adds an RCU-protected pointer to request_queue that makes it easy to
>       io-controller: Add a new interface "weight_device" for IO-Controller
>       Use disk-names to set blkio.weight_device policy
> 
> 
>  block/blk-cgroup.c     |  224 +++++++++++++++++++++++++++++++++++++++++++++---
>  block/blk-cgroup.h     |   23 ++++-
>  block/blk-sysfs.c      |    4 +
>  block/cfq-iosched.c    |   27 ++----
>  include/linux/blkdev.h |    6 +
>  5 files changed, 248 insertions(+), 36 deletions(-)
> 
> 
> 
>