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MALLOC(9)		 BSD Kernel Developer's	Manual		     MALLOC(9)

     malloc, MALLOC, free, FREE	-- kernel memory management routines

     #include <sys/types.h>
     #include <sys/malloc.h>

     void *
     malloc(unsigned long size,	struct malloc_type *type, int flags);

     MALLOC(space, cast, unsigned long size, struct malloc_type	*type,
	 int flags);

     free(void *addr, struct malloc_type *type);

     FREE(void *addr, struct malloc_type *type);

     void *
     realloc(void *addr, unsigned long size, struct malloc_type	*type,
	 int flags);

     void *
     reallocf(void *addr, unsigned long	size, struct malloc_type *type,
	 int flags);

     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.  The memory is not zeroed.  If addr is NULL, then
     free() does nothing.

     The realloc() function changes the	size of	the previously allocated mem-
     ory referenced by addr to size bytes.  The	contents of the	memory are un-
     changed up	to the lesser of the new and old sizes.	 Note that the re-
     turned value may differ from addr.	 If the	requested memory cannot	be al-
     located, NULL is returned and the memory referenced by addr is valid and
     unchanged.	 If addr is NULL, the realloc()	function behaves identically
     to	malloc() for the specified size.

     The reallocf() function call is identical to the realloc function call,
     except that it will free the passed pointer when the requested memory
     cannot be allocated.

     The MALLOC() macro	variant	is functionally	equivalent to

	   (space) = (cast)malloc((u_long)(size), type,	flags)

     and the FREE() macro variant is equivalent	to

	   free((addr),	type)

     Unlike its	standard C library counterpart (malloc(3)), the	kernel version
     takes two more arguments.	The flags argument further qualifies
     malloc()'s	operational characteristics as follows:

	     Causes malloc(), realloc(), or reallocf() to return NULL if the
	     request cannot be immediately fulfilled due to resource shortage.
	     Otherwise,	the current process may	be put to sleep	to wait	for
	     resources to be released by other processes.  If this flag	is
	     set, malloc() will	return NULL rather then	block.	Note that
	     M_WAITOK is defined to be 0, meaning that blocking	operation is
	     the default.  Also	note that M_NOWAIT is required when running in
	     an	interrupt context.

	     Causes malloc(), realloc(), or reallocf() to call asleep()	if the
	     request cannot be immediately fulfilled due to a resource short-
	     age.  M_ASLEEP is not useful alone	and should always be or'd with
	     M_NOWAIT to allow the function to call asleep() and return	NULL
	     immediately.  It is expected that the caller will at some point
	     call await() and then retry the allocation.  Depending on the
	     routine in	question, the caller may decide	to propagate the tem-
	     porary failure up the call	chain and actually have	some other
	     higher level routine block	on the async wait that the function

	     Indicates that it is Ok to	wait for resources.  It	is unconve-
	     niently defined as	0 so care should be taken never	to compare
	     against this value	directly or try	to AND it as a flag.  The de-
	     fault operation is	to block until the memory allocation succeeds.
	     malloc(), realloc(), and reallocf() can only return NULL if
	     M_NOWAIT is specified.

	     Indicates that the	system can dig into its	reserve	in order to
	     obtain the	requested memory.  This	option used to be called
	     M_KERNEL but has been renamed to something	more obvious.  This
	     option has	been deprecated	and is slowly being removed from the
	     kernel, and so should not be used with any	new programming.

     The type argument is used to perform statistics on	memory usage, and for
     basic sanity checks.  The statistics can be examined by `vmstat -m'.

     A type is defined using the malloc_type_t typedef via the

	   /* sys/something/foo_extern.h */


	   /* sys/something/foo_main.c */

	   MALLOC_DEFINE(M_FOOBUF, "foobuffers", "Buffers to foo data into the ether");

	   /* sys/something/foo_subr.c */

	   MALLOC(buf, struct foo_buf *, sizeof	*buf, M_FOOBUF,	M_NOWAIT);

     malloc(), realloc(), and reallocf() return	a kernel virtual address that
     is	suitably aligned for storage of	any type of object, or NULL if the re-
     quest could not be	satisfied (implying that M_NOWAIT was set).  If
     M_ASLEEP was set and the function returns NULL, it	will call asleep() as
     a side effect.

     The memory	allocator allocates memory in chunks that have size a power of
     two for requests up to the	size of	a page of memory.  For larger re-
     quests, one or more pages is allocated.  While it should not be relied
     upon, this	information may	be useful for optimizing the efficiency	of
     memory use.


     A kernel compiled with the	DIAGNOSTIC configuration option	attempts to
     detect memory corruption caused by	such things as writing outside the al-
     located area and imbalanced calls to the malloc() and free() functions.
     Failing consistency checks	will cause a panic or a	system console mes-

	   +o   panic: "malloc: bogus type"
	   +o   panic: "malloc: allocation too large"
	   +o   panic: "malloc: wrong bucket"
	   +o   panic: "malloc: lost data"
	   +o   panic: "free: address 0x%x out of range"
	   +o   panic: "free: type %d out of range"
	   +o   panic: "free: unaligned addr <description of object>"
	   +o   panic: "free: item modified"
	   +o   panic: "free: multiple free[s]"
	   +o   "Data modified on freelist: <description	of object>"

BSD				 June 16, 1996				   BSD


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