如何从Linux内核中的PID获取过程描述符? [英] How can I get the process descriptor from a PID in Linux kernel?

问题描述

我试图弄清楚如何从PID中获取过程描述符.

I am trying to figure out how to get the process descriptor from a PID.

来自 http://对于Linux内核2.4，www.linuxforums.org/forum/kernel/153873-getting-task_struct-process-using-its-pid.html

static inline struct task_struct *find_task_by_pid(int pid)
{
    struct task_struct *p, **htable = &pidhash[pid_hashfn(pid)];

    for(p = *htable; p && p->pid != pid; p = p->pidhash_next)
        ;

    return p;
}

链接似乎说pidhash[pid_hashfn(pid)]是指向PID值为pid的task_struct对象的指针.

The link seems to say that pidhash[pid_hashfn(pid)] is a pointer to a task_struct object whose PID is value pid.

但是从《理解Linux内核》一书中似乎并非如此，该书讨论了Linux内核2.6.11.我不确定2.6.11和2.4中的相关代码是否相同.从书中，我了解到pidhash[pid_hashfn(pid)]具有类型hlist_head，它是指向hlist_node对象的指针. hlist_node对象是task_struct对象的pids[0].pid_chain.那么如何从pidhash[pid_hashfn(pid)]获取task_struct对象?

But that doesn't seem to be true from the book Understanding The Linux Kernel, which talks about Linux kernel 2.6.11. I am not sure if the relevant code is the same in 2.6.11 and in 2.4. From the book, I learned that pidhash[pid_hashfn(pid)] has type hlist_head, which is a pointer to an hlist_node object. The hlist_node object is pids[0].pid_chain of a task_struct object. Then how can I obtain the task_struct object from pidhash[pid_hashfn(pid)]?

请注意

• 我之所以问这个问题只是出于阅读《了解Linus内核》(Linux内核2.6.11)的目的，因此我没有询问最新的Linux内核版本，尽管您也可以使用它来提到在最新的Linux内核版本中是如何完成的.

• I am asking this just for the purposes of reading Understanding the Linus Kernel (Linux kernel 2.6.11), so I am not asking about the recent Linux kernel versions, although it doesn't hurt that you can also mention how it is done in the recent Linux kernel versions.

我想我在这里遇到的困难与我以前的问题有关

I guess the difficulty I have here is related to my previous question Whose address shall the node of a linked list store: other node, or data structure having a node as a field?

谢谢.

推荐答案

在内核2.6.11中，task_struct包含数组

In kernel 2.6.11 task_struct contains array pids[PIDTYPE_MAX] so that given task placed in several hash-tables simultaniously.

pidhash 包含指针到 PIDTYPE_MAX 哈希-桌子. pidhash[i]是指向第 i 个哈希表的开头的指针.因此，pidhash[type][pid_hashfn(nr)]是指向链表的指针.

pidhash contains pointers to PIDTYPE_MAX hash-tables. pidhash[i] is a pointer to beginning of i-th hash-table. Thus, pidhash[type][pid_hashfn(nr)] is a pointer to linked list.

最好使用内核函数

It is better to find struct pid * to entry in task's [pids[type]] element with given pid type type and pid nr using kernel function find_pid(type, nr).

然后，您可以使用基于container-of的宏

Then you can convert (non-NULL) pointer to struct pid into pointer to struct task_struct using container-of-based macro pid_task.

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