BRK(2)

NAME
brk, sbrk - change data segment size

SYNOPSIS
#include <unistd.h>

char *brk(char *addr)

char *sbrk(int incr)

DESCRIPTION
Brk sets the system's idea of the lowest data segment location 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 violation 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 megabytes.

BUGS
Setting the break may fail due to a temporary lack of virtual memory under Minix-vmd. It is not possible to distinguish this from a failure caused by exceeding the maximum size of the data segment.