/*
* Replace the following string of 0s with your student number
* 000000000
*/
#include <lib.h>    // provides _syscall and message
#include <unistd.h> // provides function prototype
#include <errno.h>

int getpids(int idx, int n, int flags_mask, pid_t *pids) {
if (n < 0 || idx < 0 || idx >= NR_PROCS) {
   errno = EINVAL;
   return -1;
}
if (!n)
   return idx;

if (n > NR_PROCS)
   n = NR_PROCS;

message m;
int i = 0;
while (n > 0 && idx < NR_PROCS) {
m.m1_i1 = idx;
m.m1_i2 = flags_mask;
// get each pid, push in the the array
   pid_t pid = _syscall(PM_PROC_NR, GETPIDS, &m);

   if (pid) {
         pids[i] = pid;
         n--;
         i++;
   }

   idx++;
}

return i;
}

int getprocname(pid_t pid, char *name) {
if (pid < 0 ){
errno = EINVAL;
return -1;
}
message m;
m.m1_i1 = pid;

int result = _syscall(PM_PROC_NR, GETPROCNAME, &m);
if (result < 0 ){
errno = EINVAL;
return -1;
}
int j;
// get name from the global variable
char * n = m.m1_p1;
// copy the whole content
for(j = 0; j < PROC_NAME_LEN;j++){
name[j] = n[j];
}

return 0;
}

int getchildinf(pid_t ppid, int nchildren, int flags_mask,
struct procinf *cpinf) {

if(ppid <= 0 || nchildren < 0 || cpinf == NULL){
errno = EINVAL;
return -1;
}
message m;
int n = nchildren;
int i = 0;
int idx = 1;
while (n > 0 && idx < NR_PROCS) {
// set input
m.m1_i1 = idx;
m.m1_i2 = flags_mask;
m.m1_i3 = ppid;
// get the pid
pid_t pid = _syscall(PM_PROC_NR, GETCHILDINF, &m);

   if (pid) { // pid should be greater than 0
         cpinf[i].ppid = ppid;
         cpinf[i].pid = pid;
         n--;
         i++;
   }
   idx++;
}

return i;
}

The Minix operating system uses a microkernel architectural approac...