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

From: Nitin Gupta
Date: Thu May 10 2012 - 10:47:32 EST

On 5/10/12 10:02 AM, Konrad Rzeszutek Wilk wrote:
On Thu, May 10, 2012 at 11:03:19AM +0900, Minchan Kim wrote:
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@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk<konrad.wilk@xxxxxxxxxx>
Signed-off-by: Minchan Kim<minchan@xxxxxxxxxx>
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: 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).



Don't add new typedefs to the kernel. Just use a structure if you need

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?

struct zs {
void *ptr;

And pass that structure around?

A minor problem is that we store this handle value in a radix tree node. If we wrap it as a struct, then we will not be able to store it directly in the node -- the node will have to point to a 'struct zs'. This will unnecessarily waste sizeof(void *) for every object stored.

We could 'memcpy' struct zs to a void * and then store that directly in the radix node but not sure if that would be less ugly than just returning the handle as a void * as is done currently.

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