brk, sbrk - change data segment size
char *brk(char *addr)
char *sbrk(int incr)
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
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
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.
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
chmem(1), execve(2), malloc(3), end(3).
Minix-vmd rounds a small data segment limit up to 3 megabytes.
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.