[RFC][PATCH] flexible array implementation v3
kamezawa.hiroyu at jp.fujitsu.com
Wed Jul 22 18:44:50 PDT 2009
On Wed, 22 Jul 2009 10:53:45 -0700
Dave Hansen <dave at linux.vnet.ibm.com> wrote:
> Changes from v2:
> - renamed some of the index functions
> - added preallocation function
> - added flex_array_free_parts() for use with
> statically allocated bases
> - killed append() function
> Changes from v1:
> - to vs too typo
> - added __check_part_and_nr() and gave it a warning
> - fixed off-by-one check on __nr_part_ptrs()
> - added FLEX_ARRAY_INIT() macro
> - some kerneldoc comments about the capacity
> with various sized objects
> - comments to note lack of locking semantice
Seems nice, thank you. but a nitpick..
+struct flex_array *flex_array_alloc(int element_size, int total, gfp_t flags)
+ struct flex_array *ret;
+ int max_size = nr_base_part_ptrs() * __elements_per_part(element_size);
+ /* max_size will end up 0 if element_size > PAGE_SIZE */
+ if (total > max_size)
+ return NULL;
Can't we store "total" somewhere and do error check ?
And some magic value as following can't be defined for 'total' ?
#define FLEX_ARRAY_MAX_ELEMENTS (-1) // Use maximum flex array.
> + * flex_array_get - pull data back out of the array
> + * @element_nr: index of the element to fetch from the array
> + *
> + * Returns a pointer to the data at index @element_nr. Note
> + * that this is a copy of the data that was passed in. If you
> + * are using this to store pointers, you'll get back &ptr.
> + *
> + * Locking must be provided by the caller.
> + */
> +void *flex_array_get(struct flex_array *fa, int element_nr)
> + int part_nr = fa_element_to_part_nr(fa, element_nr);
> + struct flex_array_part *part;
> + int offset;
> + if (__check_part_nr(fa, part_nr))
> + return NULL;
return -EINVAL, here ?
(Can't we compared with stored "total" ?)
> + if (!fa->parts[part_nr])
> + return NULL;
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.
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 ;) ?
> + part = fa->parts[part_nr];
> + offset = index_inside_part(fa, element_nr);
> + return &part->elements[index_inside_part(fa, element_nr)];
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