[PATCH 0/3] dm-target: target_type improvements

[crquan]

From: Cheng Renquan <crquan@xxxxxxxxx>

The series of patches:
1. use module's refcount instead of self-maintained use field;
2. use pointer reference instead of making a copy of target_type;
3. totally remove tt_internal;

The 3rd patch may be controversial,

On Wed, Dec 17, 2008 at 7:48 PM, Alasdair G Kergon <agk@xxxxxxxxxx> wrote:
> Target registrations should be rare one-off events.  The existing trade-off
> is
> in favour of a cleaner interface (that does not expose private fields).  The
> struct target_type passed to dm_register_target is always static read-only
> data
> and perhaps that could be enforced and a pointer stored in tt_internal
> instead
> of making a copy.

But I still think it's worth it:
1. current users of struct target_type hasn't been marked with const, just
   static;
2. other similar structures (file_system_type in filesystems, packet_type in
   net core, ) all have internally used list_head for manage purpose;
   this design can avoid memory frag from kmalloc/kfree.

--
Cheng Renquan, Shenzhen, China
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