Add malloc_usable_size(3).

Discussed with:		arch@

4 files changed, 47 insertions, 3 deletions

diff --git a/lib/libc/stdlib/Makefile.inc b/lib/libc/stdlib/Makefile.inc
index 27eee7d..99ea7fb 100644
--- a/lib/libc/stdlib/Makefile.inc
+++ b/lib/libc/stdlib/Makefile.inc
@@ -46,5 +46,5 @@ MLINKS+=strtod.3 strtof.3 strtod.3 strtold.3
 MLINKS+=strtol.3 strtoll.3 strtol.3 strtoq.3 strtol.3 strtoimax.3
 MLINKS+=strtoul.3 strtoull.3 strtoul.3 strtouq.3 strtoul.3 strtoumax.3
 MLINKS+=malloc.3 calloc.3 malloc.3 free.3 malloc.3 malloc.conf.5 \
-	malloc.3 realloc.3 malloc.3 reallocf.3
+	malloc.3 realloc.3 malloc.3 reallocf.3 malloc.3 malloc_usable_size.3
 MLINKS+=tsearch.3 tdelete.3 tsearch.3 tfind.3 tsearch.3 twalk.3
diff --git a/lib/libc/stdlib/Symbol.map b/lib/libc/stdlib/Symbol.map
index 2459fe2..ff11d7a 100644
--- a/lib/libc/stdlib/Symbol.map
+++ b/lib/libc/stdlib/Symbol.map
@@ -53,6 +53,7 @@ FBSD_1.0 {
 	calloc;
 	realloc;
 	free;
+	malloc_usable_size;
 	mergesort;
 	putenv;
 	qsort_r;
diff --git a/lib/libc/stdlib/malloc.3 b/lib/libc/stdlib/malloc.3
index 9a888c5..46ce26c 100644
--- a/lib/libc/stdlib/malloc.3
+++ b/lib/libc/stdlib/malloc.3
@@ -32,11 +32,11 @@
 .\"     @(#)malloc.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd March 9, 2006
+.Dd March 28, 2006
 .Dt MALLOC 3
 .Os
 .Sh NAME
-.Nm malloc , calloc , realloc , free , reallocf
+.Nm malloc , calloc , realloc , free , reallocf , malloc_usable_size
 .Nd general purpose memory allocation functions
 .Sh LIBRARY
 .Lb libc
@@ -58,6 +58,9 @@
 .Fo \*(lp*_malloc_message\*(rp
 .Fa "const char *p1" "const char *p2" "const char *p3" "const char *p4"
 .Fc
+.In malloc_np.h
+.Ft size_t
+.Fn malloc_usable_size "const void *ptr"
 .Sh DESCRIPTION
 The
 .Fn malloc
@@ -133,6 +136,21 @@ If
 is
 .Dv NULL ,
 no action occurs.
+.Pp
+The
+.Fn malloc_usable_size
+function returns the usable size of the allocation pointed to by
+.Fa ptr .
+The return value may be larger than the size that was requested during
+allocation.
+.Fn malloc_usable_size
+is not a mechanism for in-place
+.Fn realloc ;
+rather it is provided soley as a tool for introspection purposes.
+Any discrepancy between the requested allocation size and the size reported by
+.Fn malloc_usable_size
+should not be depended on, since such behavior is entirely
+implementation-dependent.
 .Sh TUNING
 Once, when the first call is made to one of these memory allocation
 routines, various flags will be set or reset, which affect the
@@ -443,3 +461,8 @@ The
 .Fn reallocf
 function first appeared in
 .Fx 3.0 .
+.Pp
+The
+.Fn malloc_usable_size
+function first appeared in
+.Fx 7.0 .
diff --git a/lib/libc/stdlib/malloc.c b/lib/libc/stdlib/malloc.c
index 91357a0..359c98a 100644
--- a/lib/libc/stdlib/malloc.c
+++ b/lib/libc/stdlib/malloc.c
@@ -3489,6 +3489,26 @@ free(void *ptr)
  */
 /******************************************************************************/
 /*
+ * Begin non-standard functions.
+ */
+
+size_t
+malloc_usable_size(const void *ptr)
+{
+
+	assert(ptr != NULL);
+
+	if (ptr == &nil)
+		return (0);
+	else
+		return (isalloc(ptr));
+}
+
+/*
+ * End non-standard functions.
+ */
+/******************************************************************************/
+/*
  * Begin library-private functions, used by threading libraries for protection
  * of malloc during fork().  These functions are only called if the program is
  * running in threaded mode, so there is no need to check whether the program