MALLOC(9) | Kernel Developer's Manual | MALLOC(9) |
malloc
, realloc
,
free
, malloc_type_attach
,
malloc_type_detach
,
MALLOC_DEFINE
, MALLOC_DECLARE
—
#include <sys/malloc.h>
void *
malloc
(unsigned
long size, struct
malloc_type *type, int
flags);
void *
realloc
(void
*addr, unsigned long
newsize, struct
malloc_type *type, int
flags);
void
free
(void
*addr, struct malloc_type
*type);
void
malloc_type_attach
(struct
malloc_type *type);
void
malloc_type_detach
(struct
malloc_type *type);
#include
<sys/mallocvar.h>
MALLOC_DEFINE
(type,
shortdesc,
longdesc);
MALLOC_JUSTDEFINE
(type,
shortdesc,
longdesc);
MALLOC_DECLARE
(type);
The malloc
() function allocates
uninitialized memory in kernel address space for an object whose size is
specified by size. free
()
releases memory at address addr that was previously
allocated by malloc
() for re-use. Unlike
free(3),
free
() does not accept an addr
argument that is NULL
.
The realloc
() function changes the size of
the previously allocated memory referenced by addr to
size and returns a pointer to the (possibly moved)
object. The memory contents are unchanged up to the lesser of the new and
old sizes. If the new size is larger, the newly allocated memory is
uninitialized. If the requested memory cannot be allocated,
NULL
is returned and the memory referenced by
addr is unchanged. If addr is
NULL
, then realloc
() behaves
exactly as malloc
(). If the new size is 0, then
realloc
() behaves exactly as
free
().
Unlike its standard C library counterpart (malloc(3)), the kernel version takes two more arguments.
The flags argument further qualifies
malloc
() operational characteristics as follows:
M_NOWAIT
malloc
() to return
NULL
if the request cannot be immediately
fulfilled due to resource shortage. If this flag is not set (see
M_WAITOK
), malloc
() will
never return NULL
.M_WAITOK
malloc
() may call
cv_wait(9) to wait for
resources to be released by other processes, and this flag represents this
behaviour. Note that M_WAITOK
is conveniently
defined to be 0, and hence may be or'ed into the
flags argument to indicate that it's ok to wait for
resources.M_ZERO
The type argument describes the subsystem and/or use within a subsystem for which the allocated memory was needed, and is commonly used to maintain statistics about kernel memory usage and, optionally, enforce limits on this usage for certain memory types.
In addition to some built-in generic types defined by the kernel memory allocator, subsystems may define their own types.
The MALLOC_DEFINE
() macro defines a malloc
type named type with the short description
shortdesc, which must be a constant string; this
description will be used for kernel memory statistics reporting. The
longdesc argument, also a constant string, is intended
as way to place a comment in the actual type definition, and is not
currently stored in the type structure. If kernel memory statistics are
being gathered, the system will choose a reasonable default limit for the
malloc type.
The MALLOC_DECLARE
() macro is intended for
use in header files which are included by code which needs to use the malloc
type, providing the necessary extern declaration.
Code which includes <sys/malloc.h> does not need to include
<sys/mallocvar.h> to get these macro definitions. The
<sys/mallocvar.h> header file is intended for other header files which
need to use the MALLOC_DECLARE
() macro.
The malloc_type_attach
() function attaches
the malloc type type to the kernel memory
allocator.
The malloc_type_detach
() function detaches
the malloc type type previously attached with
malloc_type_attach
().
The following generic malloc types are currently defined:
M_DEVBUF
M_DMAMAP
M_FREE
M_PCB
M_SOFTINTR
M_TEMP
Other malloc types are defined by the corresponding subsystem; see the documentation for that subsystem for information its available malloc types.
malloc
() returns a kernel virtual address that is
suitably aligned for storage of any type of object.
October 14, 2018 | NetBSD 9.2 |