lkml.org 
[lkml]   [2009]   [Jul]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [RFC][PATCH] flexible array implementation v3
From
Dave Hansen wrote:
> On Thu, 2009-07-23 at 10:44 +0900, KAMEZAWA Hiroyuki wrote:

>> The caller can't know whether
>> - there are no entry or
>> - NULL(0) is stored at the array.
>>
>> Then, he has to check gotten value is valid or not by himself.
>
> I think you may be reading this bit wrong. Either that, or I badly
> miscoded it. :) The flex_array_get() code should returns NULL in cases
> of error or the *address* of the data element. It will actually return
> an address pointing into the second-level page.
>
> NULL's two meaning here are:
> 1. No element was ever put() here and thus there's no data page
> 2. Your index was out of bounds
>
> (1) is a little fuzzy here. It of course doesn't absolutely guarantee
> that no put() was done since we just use the data page's existence to
> tell. This is certainly no worse than a normal C array would be,
> though.
>
ok, maybe not necessary to handle.


>> Can't we return -ENOENT here(especially when prealloc() is called) ?
>> But ah, anyway, all-zero elements in allocated array exists ;(
>> and the user can get value from an entry never be put.
>>
>> If we can fill the first 4bytes of _unused_ index by some magic code
>> like this
>> #define FLEX_ARRAY_UNUSED_MAGIC (0xa5a5a5a5)
>> (if maintaining bitmap/status of usage is nonsense)
>> and flex_array_get() can return -ENOENT, the users will feel easy.
>>
>> Overprotection ;) ?
>
> I intentionally didn't use kzalloc() for the data pages. I figured that
> users will either initialize it themselves or pass in __GFP_ZERO. I've
> added a comment to clarify this.
>

sorry for noise.
I just felt that this code expects users know all they really do.
As said, seems nice :) thank you.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>




\
 
 \ /
  Last update: 2009-07-23 16:51    [W:0.036 / U:0.884 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site