BRK(2)                  COMMAND REFERENCE                  BRK(2)



NAME
     brk, sbrk - change data segment size

SYNOPSIS
     #include <sys/types.h>

     caddr_t brk(addr)
     caddr_t addr;

     newaddr = sbrk(incr)
     caddr_t newaddr;
     int incr;

DESCRIPTION
     The commands brk and sbrk are used to change dynamically the
     amount of space allocated for the calling process's
     contiguous heap.  The change is made by resetting the
     process's break value.  The break value is the address of
     the first location beyond the end of the contiguous heap.
     The amount of allocated space increases as the break value
     increases: brk sets the break value to addr (rounded up to
     the next multiple of the system's page size) and changes the
     allocated space accordingly.  Locations greater than addr
     and below the stack pointer are not in the address space and
     will thus cause a memory violation if accessed.

     The command sbrk adds incr more bytes to the break value and
     changes the allocated space accordingly.  A pointer to the
     start of the new area is returned in newaddr.

     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.

     The getrlimit(2) system call may be used to determine the
     maximum permissible size of the data segment; it will not be
     possible to set the break beyond the rlim_max value returned
     from a call to getrlimit, e.g. "etext + rlp->rlim_max." (See
     end(3c) for the definition of etext.)

DIAGNOSTICS
     The sbrk and brk commands will fail and no additional memory
     will be allocated if one of the following are true:

     [ENOMEM]     The limit, as set by setrlimit(2), would be
                  exceeded.

     [ENOMEM]     The maximum possible size of a data segment,
                  text segment or stack would be exceeded.  These
                  limits are MAXTSIZ, MAXDSIZ and MAXSSIZ,
                  defined in <machine/vmparam.h>.



Printed 4/6/89                                                  1

BRK(2)                  COMMAND REFERENCE                  BRK(2)



     [ENOMEM]     Insufficient space exists in the swap area to
                  support the expansion.

RETURN VALUE
     The brk command returns 0 if the break could be set,
     otherwise it returns -1; sbrk returns a pointer to the new
     data area in newaddr if the break could be set, otherwise it
     returns -1.  Both brk and sbrk set errno if there is an
     error.

CAVEATS
     Setting the break may fail due to a temporary lack of swap
     space.  It is not possible to distinguish this from a
     failure caused by exceeding the maximum size of the data
     segment without consulting getrlimit.

SEE ALSO
     execve(2), getrlimit(2), end(3c), and malloc(3c).





































Printed 4/6/89                                                  2

%%index%%
na:216,88;
sy:304,1125;
de:1429,1836;
di:3265,695;4248,106;
rv:4354,549;
ca:4903,325;
se:5228,228;
%%index%%000000000132