结合中断上下文切换和进程上下文切换分析Linux内核的一般执行过程

#include <sys/types.h>

#include <unistd.h>
#include <stdio.h>
int main (){
          pid_t pid;
          pid = fork();
　　　　　　int count = 0;
          if (pid < 0){
                  printf("error in fork!\n");
          }
          else if (pid == 0){
                  printf("child process whose process id is %d\n",getpid());
　　　　　　　　　　　count ++;　
          }
          else{
                  printf("parent process whose process id is %d\n",getpid());
         　　　　　count ++;
　　　　　　}
　　　　　　printf("count is %d/n",count);
          return 0;
}

long _do_fork(struct kernel_clone_args *args)
{
        u64 clone_flags = args->flags;
        struct completion vfork;
        struct pid *pid;
        struct task_struct *p;
        int trace = 0;
        long nr;

        /*
         * Determine whether and which event to report to ptracer.  When
         * called from kernel_thread or CLONE_UNTRACED is explicitly
         * requested, no event is reported; otherwise, report if the event
         * for the type of forking is enabled.
         */
        if (!(clone_flags & CLONE_UNTRACED)) {
                if (clone_flags & CLONE_VFORK)
                        trace = PTRACE_EVENT_VFORK;
                else if (args->exit_signal != SIGCHLD)
                        trace = PTRACE_EVENT_CLONE;
                else
                        trace = PTRACE_EVENT_FORK;

                if (likely(!ptrace_event_enabled(current, trace)))
                        trace = 0;
        }

        p = copy_process(NULL, trace, NUMA_NO_NODE, args);
        add_latent_entropy();

        if (IS_ERR(p))
                return PTR_ERR(p);

        /*
         * Do this prior waking up the new thread - the thread pointer
         * might get invalid after that point, if the thread exits quickly.
         */
        trace_sched_process_fork(current, p);

        pid = get_task_pid(p, PIDTYPE_PID);
        nr = pid_vnr(pid);

        if (clone_flags & CLONE_PARENT_SETTID)
                put_user(nr, args->parent_tid);

        if (clone_flags & CLONE_VFORK) {
                p->vfork_done = &vfork;
                init_completion(&vfork);
                get_task_struct(p);
        }

        wake_up_new_task(p);

        /* forking complete and child started to run, tell ptracer */
        if (unlikely(trace))
                ptrace_event_pid(trace, pid);

        if (clone_flags & CLONE_VFORK) { 
            if (!wait_for_vfork_done(p, &vfork))
                        ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
        }

        put_pid(pid);
        return nr;
}

static int do_execve_common(struct filename *filename,struct user_arg_ptr argv,struct user_arg_ptr envp)
{
    struct linux_binprm *bprm;  
    struct file *file;
    struct files_struct *displaced;
    int retval;
    current->flags &= ~PF_NPROC_EXCEEDED;  
    retval = unshare_files(&displaced);  
    bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
    retval = prepare_bprm_creds(bprm);   
    check_unsafe_exec(bprm);             
    current->in_execve = 1;
    file = do_open_exec(filename);       
    sched_exec();
    bprm->file = file;
    bprm->filename = bprm->interp = filename->name;
    retval = bprm_mm_init(bprm);       
    bprm->argc = count(argv, MAX_ARG_STRINGS);
    bprm->envc = count(envp, MAX_ARG_STRINGS);
    retval = prepare_binprm(bprm);     
    retval = copy_strings_kernel(1, &bprm->filename, bprm);
    bprm->exec = bprm->p;
    retval = copy_strings(bprm->envc, envp, bprm);
    retval = copy_strings(bprm->argc, argv, bprm);
    
    <strong>retval = exec_binprm(bprm);</strong>
    
    current->fs->in_exec = 0;
    current->in_execve = 0;
    acct_update_integrals(current);
    task_numa_free(current);
    free_bprm(bprm);
    putname(filename);
    if (displaced)
        put_files_struct(displaced);
    return retval;
}