[src/trunk]: src/sys Add M_CANFAIL malloc(9) flag. This flag changes behaviou...

[jdolecek <jdolecek%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/c93e93986fab
branches:  trunk
changeset: 518719:c93e93986fab
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Tue Dec 04 20:13:19 2001 +0000

description:
Add M_CANFAIL malloc(9) flag. This flag changes behaviour in M_WAITOK
case when the requested memory size can't ever be granted - instead
of panic, malloc(9) would return failure (NULL).
Note kernel code should do proper bound checking, rather than
depend on M_CANFAIL. This flag is only supposed to be used in very
special cases, where common bound checking is not appropriate.

Discussed on tech-kern@, name ``M_CANFAIL'' suggested by Chuck Cranor.

diffstat:

 sys/kern/kern_malloc.c |  6 +++---
 sys/sys/malloc.h       |  9 +++++----
 2 files changed, 8 insertions(+), 7 deletions(-)

diffs (51 lines):

diff -r 428dd9daedd9 -r c93e93986fab sys/kern/kern_malloc.c
--- a/sys/kern/kern_malloc.c    Tue Dec 04 20:00:15 2001 +0000
+++ b/sys/kern/kern_malloc.c    Tue Dec 04 20:13:19 2001 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_malloc.c,v 1.67 2001/11/30 01:54:21 enami Exp $   */
+/*     $NetBSD: kern_malloc.c,v 1.68 2001/12/04 20:13:19 jdolecek Exp $        */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All rights reserved.
@@ -37,7 +37,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_malloc.c,v 1.67 2001/11/30 01:54:21 enami Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_malloc.c,v 1.68 2001/12/04 20:13:19 jdolecek Exp $");
 
 #include "opt_lockdebug.h"
 
@@ -279,7 +279,7 @@
                         * are completely free and which are in buckets
                         * with too many free elements.)
                         */
-                       if ((flags & M_NOWAIT) == 0)
+                       if ((flags & (M_NOWAIT|M_CANFAIL)) == 0)
                                panic("malloc: out of space in kmem_map");
                        splx(s);
                        return ((void *) NULL);
diff -r 428dd9daedd9 -r c93e93986fab sys/sys/malloc.h
--- a/sys/sys/malloc.h  Tue Dec 04 20:00:15 2001 +0000
+++ b/sys/sys/malloc.h  Tue Dec 04 20:13:19 2001 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: malloc.h,v 1.68 2001/11/17 03:50:27 lukem Exp $        */
+/*     $NetBSD: malloc.h,v 1.69 2001/12/04 20:13:20 jdolecek Exp $     */
 
 /*
  * Copyright (c) 1987, 1993
@@ -48,10 +48,11 @@
 /*
  * flags to malloc
  */
-#define        M_WAITOK        0x0000
-#define        M_NOWAIT        0x0001
+#define        M_WAITOK        0x0000  /* can wait for resources */
+#define        M_NOWAIT        0x0001  /* do not wait for resources */
 #define        M_ZERO          0x0002  /* zero the allocation */
-
+#define        M_CANFAIL       0x0004  /* can fail if requested memory can't ever
+                                * be allocated */
 /*
  * Types of memory to be allocated
  */