关于daemonize()

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lock_kernel();
siginitsetinv(¤t->blocked, SHUTDOWN_SIGS);
daemonize();
target_data.thread_id = current;
unlock_kernel();
注：SHUTDOWN_SIGS前面定义为# define SHUTDOWN_SIGS (sigmask(SIGKILL)|sigmask(SIGINT)|sigmask(SIGTERM)) target_data是前面定义的一个全局数据结构，thread_id是它的一个task_struct 结构的一个成员。这里的daemonize函数是什么作用?

   1. linux-2.4.20\kernel\sched.c start from line 1283:     2.      3. /*    4. *        Put all the gunge required to become a kernel thread without    5. *        attached user resources in one place where it belongs.    6. */     7.      8. void daemonize(void)     9. {    10.         struct fs_struct *fs;    11.     12.     13.         /*   14.          * If we were started as result of loading a module, close all of the   15.          * user space pages.  We don't need them, and if we didn't close them   16.          * they would be locked into memory.   17.          */    18.         exit_mm(current); //因为是内核级daemon，所以不会再需要用户级的内存页面，释放之。这些页面是因为加载模块而申请到的。    19.     20.         current->session = 1;    21.         current->pgrp = 1;    22.         current->tty = NULL;//因为是内核级daemon，所以不再需要终端控制台，所属会话为init会话，parent group为1（init），这样就成为init任务的一部分了。下面的代码则是释放文件系统相关资源，并且转为指向init任务的文件资源。    23.         /* Become as one with the init task */    24.     25.         exit_fs(current);        /* current->fs->count--; */    26.         fs = init_task.fs;    27.         current->fs = fs;    28.         atomic_inc(&fs->count);    29.         exit_files(current);    30.         current->files = init_task.files;    31.         atomic_inc(*t->files->count);    32. }