NAME
brk, sbrk - change data segment size
SYNOPSIS
#include <unistd.h>
int brk(char *addr)
char *sbrk(int incr)
DESCRIPTION
Brk sets the system's idea of the lowest data segment loca-
tion not used by the program (called the break) to addr.
Locations greater than addr and below the stack pointer are
not in the address space and will thus cause a memory viola-
tion if accessed.
In the alternate function sbrk, incr more bytes are added to
the program's data space and a pointer to the start of the
new area is returned.
When a program begins execution via execve the break is set
at the highest location defined by the program and data
storage areas. Ordinarily, therefore, only programs with
growing data areas need to use sbrk.
RETURN VALUE
The address of the new break is returned if brk succeeds; -1
if the program requests more memory than the system limit.
Sbrk returns -1 if the break could not be set.
ERRORS
Sbrk will fail and no additional memory will be allocated if
one of the following are true:
[ENOMEM] The maximum possible size of a data segment
(as set by chmem(1)) was exceeded.
[ENOMEM] Insufficient virtual memory space existed to
support the expansion. (Minix-vmd)
SEE ALSO
chmem(1), execve(2), malloc(3), end(3).
NOTES
Minix-vmd rounds a small data segment limit up to 3 mega-
bytes.
BUGS
Setting the break may fail due to a temporary lack of vir-
tual memory under Minix-vmd. It is not possible to distin-
guish this from a failure caused by exceeding the maximum
size of the data segment.