_brk.c

minux的源代码,一个非常小的操作系统

#include <lib.h>
#define brk	_brk
#define sbrk	_sbrk
#include <unistd.h>

extern char *_brksize;

/* Both OSF/1 and SYSVR4 man pages specify that brk(2) returns int.
 * However, BSD4.3 specifies that brk() returns char*.  POSIX omits
 * brk() on the grounds that it imposes a memory model on an architecture.
 * For this reason, brk() and sbrk() are not in the lib/posix directory.
 * On the other hand, they are so crucial to correct operation of so many
 * parts of the system, that we have chosen to hide the name brk using _brk,
 * as with system calls.  In this way, if a user inadvertently defines a
 * procedure brk, MINIX may continue to work because the true call is _brk.
 */
PUBLIC int brk(addr)
char *addr;
{
  message m;

  m.m1_p1 = addr;
  if (_syscall(MM, BRK, &m) < 0) return(-1);
  _brksize = m.m2_p1;
  return(0);
}


PUBLIC char *sbrk(incr)
int incr;
{
  char *newsize, *oldsize;

  oldsize = _brksize;
  newsize = _brksize + incr;
  if (incr > 0 && newsize < oldsize || incr < 0 && newsize > oldsize)
	return( (char *) -1);
  if (brk(newsize) == 0)
	return(oldsize);
  else
	return( (char *) -1);
}