1.\" 2.\" Copyright (c) 1996 The NetBSD Foundation, Inc. 3.\" All rights reserved. 4.\" 5.\" This code is derived from software contributed to The NetBSD Foundation 6.\" by Paul Kranenburg. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the NetBSD 19.\" Foundation, Inc. and its contributors. 20.\" 4. Neither the name of The NetBSD Foundation nor the names of its 21.\" contributors may be used to endorse or promote products derived 22.\" from this software without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 25.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 26.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 27.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE 28.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 29.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 30.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 31.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 32.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 33.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 34.\" POSSIBILITY OF SUCH DAMAGE. 35.\" 36.\" $NetBSD: malloc.9,v 1.3 1996/11/11 00:05:11 lukem Exp $ 37.\" $FreeBSD$ 38.\" 39.Dd June 12, 2003 40.Dt MALLOC 9 41.Os 42.Sh NAME 43.Nm malloc , 44.Nm MALLOC , 45.Nm free , 46.Nm FREE , 47.Nm realloc , 48.Nm reallocf , 49.Nm MALLOC_DEFINE , 50.Nm MALLOC_DECLARE 51.Nd kernel memory management routines 52.Sh SYNOPSIS 53.In sys/types.h 54.In sys/malloc.h 55.Ft void * 56.Fn malloc "unsigned long size" "struct malloc_type *type" "int flags" 57.Fn MALLOC space cast "unsigned long size" "struct malloc_type *type" "int flags" 58.Ft void 59.Fn free "void *addr" "struct malloc_type *type" 60.Fn FREE "void *addr" "struct malloc_type *type" 61.Ft void * 62.Fn realloc "void *addr" "unsigned long size" "struct malloc_type *type" "int flags" 63.Ft void * 64.Fn reallocf "void *addr" "unsigned long size" "struct malloc_type *type" "int flags" 65.Fn MALLOC_DECLARE type 66.In sys/param.h 67.In sys/malloc.h 68.In sys/kernel.h 69.Fn MALLOC_DEFINE type shortdesc longdesc 70.Sh DESCRIPTION 71The 72.Fn malloc 73function allocates uninitialized memory in kernel address space for an 74object whose size is specified by 75.Fa size . 76.Pp 77The 78.Fn free 79function releases memory at address 80.Fa addr 81that was previously allocated by 82.Fn malloc 83for re-use. 84The memory is not zeroed. 85If 86.Fa addr 87is 88.Dv NULL , 89then 90.Fn free 91does nothing. 92.Pp 93The 94.Fn realloc 95function changes the size of the previously allocated memory referenced by 96.Fa addr 97to 98.Fa size 99bytes. 100The contents of the memory are unchanged up to the lesser of the new and 101old sizes. 102Note that the returned value may differ from 103.Fa addr . 104If the requested memory cannot be allocated, 105.Dv NULL 106is returned and the memory referenced by 107.Fa addr 108is valid and unchanged. 109If 110.Fa addr 111is 112.Dv NULL , 113the 114.Fn realloc 115function behaves identically to 116.Fn malloc 117for the specified size. 118.Pp 119The 120.Fn reallocf 121function is identical to 122.Fn realloc 123except that it 124will free the passed pointer when the requested memory cannot be allocated. 125.Pp 126The 127.Fn MALLOC 128macro variant is functionally equivalent to 129.Bd -literal -offset indent 130(space) = (cast)malloc((u_long)(size), type, flags) 131.Ed 132.Pp 133and the 134.Fn FREE 135macro variant is equivalent to 136.Bd -literal -offset indent 137free((addr), type) 138.Ed 139.Pp 140Unlike its standard C library counterpart 141.Pq Xr malloc 3 , 142the kernel version takes two more arguments. 143The 144.Fa flags 145argument further qualifies 146.Fn malloc Ns 's 147operational characteristics as follows: 148.Bl -tag -width indent 149.It Dv M_ZERO 150Causes the allocated memory to be set to all zeros. 151.It Dv M_NOWAIT 152Causes 153.Fn malloc , 154.Fn realloc , 155and 156.Fn reallocf 157to return 158.Dv NULL 159if the request cannot be immediately fulfilled due to resource shortage. 160Note that 161.Dv M_NOWAIT 162is required when running in an interrupt context. 163.It Dv M_WAITOK 164Indicates that it is OK to wait for resources. 165If the request cannot be immediately fulfilled, the current process is put 166to sleep to wait for resources to be released by other processes. 167The 168.Fn malloc , 169.Fn realloc , 170and 171.Fn reallocf 172functions cannot return 173.Dv NULL 174if 175.Dv M_WAITOK 176is specified. 177.It Dv M_USE_RESERVE 178Indicates that the system can dig into its reserve in order to obtain the 179requested memory. 180This option used to be called 181.Dv M_KERNEL 182but has been renamed to something more obvious. 183This option has been deprecated and is slowly being removed from the kernel, 184and so should not be used with any new programming. 185.El 186.Pp 187Exactly one of either 188.Dv M_WAITOK 189or 190.Dv M_NOWAIT 191must be specified. 192.Pp 193The 194.Fa type 195argument is used to perform statistics on memory usage, and for 196basic sanity checks. 197It can be used to identify multiple allocations. 198The statistics can be examined by 199.Sq vmstat -m . 200.Pp 201A 202.Fa type 203is defined using 204.Vt "struct malloc_type" 205via the 206.Fn MALLOC_DECLARE 207and 208.Fn MALLOC_DEFINE 209macros. 210.Bd -literal -offset indent 211/* sys/something/foo_extern.h */ 212 213MALLOC_DECLARE(M_FOOBUF); 214 215/* sys/something/foo_main.c */ 216 217MALLOC_DEFINE(M_FOOBUF, "foobuffers", "Buffers to foo data into the ether"); 218 219/* sys/something/foo_subr.c */ 220 221\&... 222MALLOC(buf, struct foo_buf *, sizeof *buf, M_FOOBUF, M_NOWAIT); 223 224.Ed 225.Pp 226In order to use 227.Fn MALLOC_DEFINE , 228one must include 229.In sys/param.h 230(instead of 231.In sys/types.h ) 232and 233.In sys/kernel.h . 234.Sh IMPLEMENTATION NOTES 235The memory allocator allocates memory in chunks that have size a power 236of two for requests up to the size of a page of memory. 237For larger requests, one or more pages is allocated. 238While it should not be relied upon, this information may be useful for 239optimizing the efficiency of memory use. 240.Pp 241Programmers should be careful not to confuse the malloc flags 242.Dv M_NOWAIT 243and 244.Dv M_WAITOK 245with the 246.Xr mbuf 9 247flags 248.Dv M_DONTWAIT 249and 250.Dv M_TRYWAIT . 251.Sh CONTEXT 252.Fn malloc , 253.Fn realloc 254and 255.Fn reallocf 256may not be called from fast interrupts handlers. 257When called from threaded interrupts, 258.Fa flags 259must contain 260.Dv M_NOWAIT . 261.Pp 262.Fn malloc , 263.Fn realloc 264and 265.Fn reallocf 266may sleep when called with 267.Dv M_WAITOK . 268.Fn free 269never sleeps. 270.Pp 271Any calls to 272.Fn malloc 273(even with 274.Dv M_NOWAIT ) 275or 276.Fn free 277when holding a 278.Xr vnode 9 279interlock, will cause a LOR (Lock Order Reversal) due to the 280intertwining of VM Objects and Vnodes. 281.Sh RETURN VALUES 282The 283.Fn malloc , 284.Fn realloc , 285and 286.Fn reallocf 287functions return a kernel virtual address that is suitably aligned for 288storage of any type of object, or 289.Dv NULL 290if the request could not be satisfied (implying that 291.Dv M_NOWAIT 292was set). 293.Sh DIAGNOSTICS 294A kernel compiled with the 295.Dv INVARIANTS 296configuration option attempts to detect memory corruption caused by 297such things as writing outside the allocated area and imbalanced calls to the 298.Fn malloc 299and 300.Fn free 301functions. 302Failing consistency checks will cause a panic or a system console 303message. 304.Sh SEE ALSO 305.Xr vmstat 8 , 306.Xr contigmalloc 9 , 307.Xr memguard 9 , 308.Xr vnode 9 309