minix/kernel/system/do_fork.c

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/* The kernel call implemented in this file:
* m_type: SYS_FORK
*
* The parameters for this kernel call are:
* m1_i1: PR_PROC_NR (child's process table slot)
* m1_i2: PR_PPROC_NR (parent, process that forked)
*/
#include "../system.h"
#include <signal.h>
#if (CHIP == INTEL)
#include "../protect.h"
#endif
#if USE_FORK
/*===========================================================================*
* do_fork *
*===========================================================================*/
PUBLIC int do_fork(m_ptr)
register message *m_ptr; /* pointer to request message */
{
/* Handle sys_fork(). PR_PPROC_NR has forked. The child is PR_PROC_NR. */
#if (CHIP == INTEL)
reg_t old_ldt_sel;
#endif
register struct proc *rpc; /* child process pointer */
struct proc *rpp; /* parent process pointer */
int i;
rpp = proc_addr(m_ptr->PR_PPROC_NR);
rpc = proc_addr(m_ptr->PR_PROC_NR);
if (isemptyp(rpp) || ! isemptyp(rpc)) return(EINVAL);
/* Copy parent 'proc' struct to child. And reinitialize some fields. */
#if (CHIP == INTEL)
old_ldt_sel = rpc->p_ldt_sel; /* backup local descriptors */
*rpc = *rpp; /* copy 'proc' struct */
rpc->p_ldt_sel = old_ldt_sel; /* restore descriptors */
#else
*rpc = *rpp; /* copy 'proc' struct */
#endif
rpc->p_nr = m_ptr->PR_PROC_NR; /* this was obliterated by copy */
/* Only one in group should have SIGNALED, child doesn't inherit tracing. */
rpc->p_rts_flags |= NO_MAP; /* inhibit process from running */
rpc->p_rts_flags &= ~(SIGNALED | SIG_PENDING | P_STOP);
sigemptyset(&rpc->p_pending);
rpc->p_reg.retreg = 0; /* child sees pid = 0 to know it is child */
rpc->p_user_time = 0; /* set all the accounting times to 0 */
rpc->p_sys_time = 0;
/* Parent and child have to share the quantum that the forked process had,
* so that queued processes do not have to wait longer because of the fork.
* If the time left is odd, the child gets an extra tick.
*/
rpc->p_ticks_left = (rpc->p_ticks_left + 1) / 2;
rpp->p_ticks_left = rpp->p_ticks_left / 2;
/* If the parent is a privileged process, take away the privileges from the
* child process and inhibit it from running by setting the NO_PRIV flag.
* The caller should explicitely set the new privileges before executing.
*/
if (priv(rpp)->s_flags & SYS_PROC) {
rpc->p_priv = priv_addr(USER_PRIV_ID);
rpc->p_rts_flags |= NO_PRIV;
}
return(OK);
}
#endif /* USE_FORK */