9b599bac1d
- This patch removes the time slice split between parent and child in fork. - The time slice of the parent remains unchanged and the child does not have any. - If the process has a scheduler, the scheduler must assign the quantum and priority of the new process and let it run. - If the child does not inherit a scheduler, it is scheduled by the dummy default kernel policy. (servers, drivers, etc.) - In theory, the scheduler can change the quantum even of the parent process and implement any policy for splitting the quantum as neither the parent nor the child are runnable. Sending the out-of_quantum message on behalf of the processes may look like the right solution, however, the scheduler would probably handle the message before the whole fork protocol is finished. This way the scheduler has absolute control when the process should become runnable.
124 lines
4 KiB
C
124 lines
4 KiB
C
/* The kernel call implemented in this file:
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* m_type: SYS_FORK
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*
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* The parameters for this kernel call are:
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* m1_i1: PR_ENDPT (parent, process that forked)
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* m1_i2: PR_SLOT (child's process table slot)
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* m1_p1: PR_MEM_PTR (new memory map for the child)
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* m1_i3: PR_FORK_FLAGS (fork flags)
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*/
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#include "kernel/system.h"
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#include "kernel/vm.h"
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#include <signal.h>
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#include <string.h>
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#include <assert.h>
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#include <minix/endpoint.h>
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#if USE_FORK
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/*===========================================================================*
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* do_fork *
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*===========================================================================*/
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PUBLIC int do_fork(struct proc * caller, message * m_ptr)
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{
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/* Handle sys_fork(). PR_ENDPT has forked. The child is PR_SLOT. */
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#if (_MINIX_CHIP == _CHIP_INTEL)
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reg_t old_ldt_sel;
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void *old_fpu_save_area_p;
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#endif
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register struct proc *rpc; /* child process pointer */
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struct proc *rpp; /* parent process pointer */
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struct mem_map *map_ptr; /* virtual address of map inside caller (PM) */
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int gen, r;
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int p_proc;
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if(!isokendpt(m_ptr->PR_ENDPT, &p_proc))
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return EINVAL;
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rpp = proc_addr(p_proc);
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rpc = proc_addr(m_ptr->PR_SLOT);
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if (isemptyp(rpp) || ! isemptyp(rpc)) return(EINVAL);
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assert(!(rpp->p_misc_flags & MF_DELIVERMSG));
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/* needs to be receiving so we know where the message buffer is */
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if(!RTS_ISSET(rpp, RTS_RECEIVING)) {
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printf("kernel: fork not done synchronously?\n");
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return EINVAL;
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}
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map_ptr= (struct mem_map *) m_ptr->PR_MEM_PTR;
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/* Copy parent 'proc' struct to child. And reinitialize some fields. */
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gen = _ENDPOINT_G(rpc->p_endpoint);
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#if (_MINIX_CHIP == _CHIP_INTEL)
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old_ldt_sel = rpc->p_seg.p_ldt_sel; /* backup local descriptors */
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old_fpu_save_area_p = rpc->p_fpu_state.fpu_save_area_p;
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#endif
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*rpc = *rpp; /* copy 'proc' struct */
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#if (_MINIX_CHIP == _CHIP_INTEL)
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rpc->p_seg.p_ldt_sel = old_ldt_sel; /* restore descriptors */
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rpc->p_fpu_state.fpu_save_area_p = old_fpu_save_area_p;
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if(rpp->p_misc_flags & MF_FPU_INITIALIZED)
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memcpy(rpc->p_fpu_state.fpu_save_area_p,
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rpp->p_fpu_state.fpu_save_area_p,
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FPU_XFP_SIZE);
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#endif
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if(++gen >= _ENDPOINT_MAX_GENERATION) /* increase generation */
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gen = 1; /* generation number wraparound */
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rpc->p_nr = m_ptr->PR_SLOT; /* this was obliterated by copy */
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rpc->p_endpoint = _ENDPOINT(gen, rpc->p_nr); /* new endpoint of slot */
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rpc->p_reg.retreg = 0; /* child sees pid = 0 to know it is child */
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rpc->p_user_time = 0; /* set all the accounting times to 0 */
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rpc->p_sys_time = 0;
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rpc->p_reg.psw &= ~TRACEBIT; /* clear trace bit */
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rpc->p_misc_flags &= ~(MF_VIRT_TIMER | MF_PROF_TIMER | MF_SC_TRACE);
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rpc->p_virt_left = 0; /* disable, clear the process-virtual timers */
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rpc->p_prof_left = 0;
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/*
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* if the child process inherited a scheduler, the child process is not
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* runnable until it's scheduled. Otherwise the default kernel policy applies.
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* This is only the case of system servers, drivers and similar sensitive
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* processes
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*/
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if (rpc->p_scheduler)
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RTS_SET(rpc, RTS_NO_QUANTUM);
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/* If the parent is a privileged process, take away the privileges from the
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* child process and inhibit it from running by setting the NO_PRIV flag.
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* The caller should explicitely set the new privileges before executing.
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*/
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if (priv(rpp)->s_flags & SYS_PROC) {
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rpc->p_priv = priv_addr(USER_PRIV_ID);
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rpc->p_rts_flags |= RTS_NO_PRIV;
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}
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/* Calculate endpoint identifier, so caller knows what it is. */
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m_ptr->PR_ENDPT = rpc->p_endpoint;
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m_ptr->PR_FORK_MSGADDR = (char *) rpp->p_delivermsg_vir;
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/* Install new map */
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r = newmap(caller, rpc, map_ptr);
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FIXLINMSG(rpc);
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/* Don't schedule process in VM mode until it has a new pagetable. */
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if(m_ptr->PR_FORK_FLAGS & PFF_VMINHIBIT) {
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RTS_SET(rpc, RTS_VMINHIBIT);
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}
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/*
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* Only one in group should have RTS_SIGNALED, child doesn't inherit tracing.
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*/
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RTS_UNSET(rpc, (RTS_SIGNALED | RTS_SIG_PENDING | RTS_P_STOP));
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sigemptyset(&rpc->p_pending);
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return r;
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}
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#endif /* USE_FORK */
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