kernel - Question about writing my own system call in FreeBSD -


ok, finish reading implementation of kill(2) of freebsd, , trying write own "kill". system call takes uid , signum , sends signal processes owned uid, excluding calling process.

how can pass uid system call? in kill(2), pid in argument struct kill_args. there structure contains uid way struct kill_args contains pid? if not, can define structure outside kernel?

it's easy, kind of involved process. here's module installs system call.

include bunch of stuff

#include <sys/types.h> #include <sys/param.h> #include <sys/proc.h> #include <sys/module.h> #include <sys/sysent.h> #include <sys/kernel.h> #include <sys/systm.h> #include <sys/sysproto.h>

define structure hold arguments

struct mykill_args {     int pid;     int signo; };

define handling function

static int mykill(struct thread *td, void *args) {     struct mykill_args *uap = args;      uprintf("mykill called. pid=%d, signo=%d\n", uap->pid, uap->signo);      return 0; }

you need sysent object

static struct sysent mykill_sysent = {     2,          /* number of arguments */     mykill      /* function handling system call */ };

and offset @ system call installed.

/* choose "the next" value later. */ static int offset = no_syscall;

load function

static int load(struct module *module, int cmd, void *arg) {     int error = 0;      switch (cmd) {         case mod_load:             uprintf("loading module. installing syscall at"                 " offset %d\n", offset);             break;         case mod_unload:             uprintf("unloading module. syscall uninstalled from"                 " offset %d\n", offset);             break;         default:             error = eopnotsupp;             break;     }      return error; }

install system call

syscall_module(mykill, &offset, &mykill_sysent, load, null);

you can run system call using syscall(2). or using perl :)). here's example

[root@aiur /home/cnicutar/kld-syscall]# kldload ./mykill.ko loading module. installing syscall @ offset 210  [cnicutar@aiur ~/kld-syscall]$ perl -e 'syscall(210, 30, 15);' mykill called. pid=30, signo=15

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