Re: [PATCH 3/4] zsmalloc use zs_handle instead of void *

From: Minchan Kim <minchan@kernel.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>,
	Nitin Gupta <ngupta@vflare.org>,
	Dan Magenheimer <dan.magenheimer@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH 3/4] zsmalloc use zs_handle instead of void *
Date: Thu, 10 May 2012 11:03:19 +0900	[thread overview]
Message-ID: <4FAB21E7.7020703@kernel.org> (raw)
In-Reply-To: <20120509201918.GA7288@kroah.com>

On 05/10/2012 05:19 AM, Greg Kroah-Hartman wrote:

> On Fri, May 04, 2012 at 11:24:54AM +0900, Minchan Kim wrote:
>> On 05/04/2012 12:23 AM, Seth Jennings wrote:
>>
>>> On 05/03/2012 08:32 AM, Nitin Gupta wrote:
>>>
>>>> On 5/3/12 2:40 AM, Minchan Kim wrote:
>>>>> We should use zs_handle instead of void * to avoid any
>>>>> confusion. Without this, users may just treat zs_malloc return value as
>>>>> a pointer and try to deference it.
>>>>>
>>>>> Cc: Dan Magenheimer<dan.magenheimer@oracle.com>
>>>>> Cc: Konrad Rzeszutek Wilk<konrad.wilk@oracle.com>
>>>>> Signed-off-by: Minchan Kim<minchan@kernel.org>
>>>>> ---
>>>>>   drivers/staging/zcache/zcache-main.c     |    8 ++++----
>>>>>   drivers/staging/zram/zram_drv.c          |    8 ++++----
>>>>>   drivers/staging/zram/zram_drv.h          |    2 +-
>>>>>   drivers/staging/zsmalloc/zsmalloc-main.c |   28
>>>>> ++++++++++++++--------------
>>>>>   drivers/staging/zsmalloc/zsmalloc.h      |   15 +++++++++++----
>>>>>   5 files changed, 34 insertions(+), 27 deletions(-)
>>>>
>>>> This was a long pending change. Thanks!
>>>
>>>
>>> The reason I hadn't done it before is that it introduces a checkpatch
>>> warning:
>>>
>>> WARNING: do not add new typedefs
>>> #303: FILE: drivers/staging/zsmalloc/zsmalloc.h:19:
>>> +typedef void * zs_handle;
>>>
>>
>>
>> Yes. I did it but I think we are (a) of chapter 5: Typedefs in Documentation/CodingStyle.
>>
>>  (a) totally opaque objects (where the typedef is actively used to _hide_
>>      what the object is).
>>
>> No?
> 
> No.
> 
> Don't add new typedefs to the kernel.  Just use a structure if you need
> to.

I tried it but failed because there were already tightly coupling between [zcache|zram]
and zsmalloc. 
They already knows handle's internal well so they used it as pointer, even zcache keeps
handle's value as some key in tmem_put and tmem_get
AFAIK, ramster also will use zsmalloc sooner or later and add more coupling codes. Sigh.
Please fix it as soon as possible.

Dan, Seth
Any ideas?

> 
> Vague "handles" are almost never what you want to do in Linux, sorry, I
> can't take this patch.
> 
> greg k-h
> 
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-- 
Kind regards,
Minchan Kim