Hello,

This is an updated version of "dm/md dependency tree in sysfs" patch.
For example, if dm-0 maps to sda, we'll have following symlinks;
   /sys/block/dm-0/slaves/sda --> /sys/block/sda
   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0

Difference from the previous version is a fix for a problem
of calling possibly-sleeping function inside the fast path.
There were 3 such calls in my previous bd_claim patch:
   - kmalloc(GFP_KERNEL)
   - sysfs_create_symlink()
   - sysfs_remove_symlink()
The allocation code is moved outside of locks.
Symlink operations needs to be atomic, so they are moved out
of global bdev_lock and use bdev->bd_sem instead.

Comments are welcome.

I tested this on 2.6.16-rc6 and 2.6.16-rc6-mm1 with both
CONFIG_PREEMPT and CONFIG_DEBUG_SPINLOCK_SLEEP enabled
and saw no warnings in kernel log.

Patches included are:

  1. [PATCH 1/7] kobject_add_dir
     Adding kobject_add_dir() function which creates
     a subdirectory for a given kobject.

  2. [PATCH 2/7] add holders/slaves subdirectory to /sys/block
     Creating "slaves" and "holders" directories in /sys/block/≤disk>,
     creating "holders" directory under /sys/block/≤disk>/<partition>

  3. [PATCH 3/7] bd_claim_by_kobject
     Adding bd_claim_by_kobject() function which takes kobject as
     additional signature of holder device and creates sysfs symlinks
     between holder device and claimed device.
     bd_release_from_kobject() is a counter part of bd_claim_by_kobject.

  4. [PATCH 4/7] bd_claim_by_disk
     Variants which take gendisk instead of kobject
     and do kobject_{get,put}(&gendisk->kobj).

  5. [PATCH 5/7] md to use bd_claim_by_disk
     Use bd_claim_by_disk.

  6. [PATCH 6/7] dm to use bd_claim_by_disk
     Use bd_claim_by_disk.

  7. [PATCH 7/7] conver bd_sem to bd_mutex
     bd_sem is converted to bd_mutex in 2.6.16-rc6-mm1.
     The patch follows that conversion.

Patch 3 includes the fix mentioned above.

Patch 6 depends on dm-table-store-md.patch and dm-tidy-mdptr.patch
which were committed to -mm yesterday.

Patch 7 depends on sem2mutex-blockdev-2.patch in 2.6.16-rc6-mm1.

Thanks,
-- 
Jun'ichi Nomura, NEC Solutions (America), Inc.