+===================================
Using flexible arrays in the kernel
-Last updated for 2.6.32
-Jonathan Corbet <corbet@lwn.net>
+===================================
+
+:Updated: Last updated for 2.6.32
+:Author: Jonathan Corbet <corbet@lwn.net>
Large contiguous memory allocations can be unreliable in the Linux kernel.
Kernel programmers will sometimes respond to this problem by allocating
locking at all; if concurrent access to an array is possible, then the
caller must arrange for appropriate mutual exclusion.
-The creation of a flexible array is done with:
+The creation of a flexible array is done with::
#include <linux/flex_array.h>
the current code, using flags to ask for high memory is likely to lead to
notably unpleasant side effects.
-It is also possible to define flexible arrays at compile time with:
+It is also possible to define flexible arrays at compile time with::
DEFINE_FLEX_ARRAY(name, element_size, total);
This macro will result in a definition of an array with the given name; the
element size and total will be checked for validity at compile time.
-Storing data into a flexible array is accomplished with a call to:
+Storing data into a flexible array is accomplished with a call to::
int flex_array_put(struct flex_array *array, unsigned int element_nr,
void *src, gfp_t flags);
memory allocator would be a bad thing. That can be avoided by using
GFP_ATOMIC for the flags value, but, often, there is a better way. The
trick is to ensure that any needed memory allocations are done before
-entering atomic context, using:
+entering atomic context, using::
int flex_array_prealloc(struct flex_array *array, unsigned int start,
unsigned int nr_elements, gfp_t flags);
flex_array_put() call on an element in that range is guaranteed not to
block.
-Getting data back out of the array is done with:
+Getting data back out of the array is done with::
void *flex_array_get(struct flex_array *fa, unsigned int element_nr);
Note that, if array elements are allocated with __GFP_ZERO, they will be
initialized to zero and this poisoning will not happen.
-Individual elements in the array can be cleared with:
+Individual elements in the array can be cleared with::
int flex_array_clear(struct flex_array *array, unsigned int element_nr);
zero. If storage for the indicated element is not allocated for the array,
flex_array_clear() will return -EINVAL instead. Note that clearing an
element does not release the storage associated with it; to reduce the
-allocated size of an array, call:
+allocated size of an array, call::
int flex_array_shrink(struct flex_array *array);
FLEX_ARRAY_FREE bytes, so (1) it can be expensive, and (2) it will not work
if the array's pages are allocated with __GFP_ZERO.
-It is possible to remove all elements of an array with a call to:
+It is possible to remove all elements of an array with a call to::
void flex_array_free_parts(struct flex_array *array);
This call frees all elements, but leaves the array itself in place.
-Freeing the entire array is done with:
+Freeing the entire array is done with::
void flex_array_free(struct flex_array *array);