Need clarification on the content given in the Linux Kernel by Robert Love

Question

I am new in LKD and I was reading book by Robert Love. I stuck in understand one concept as follow.

Similarly, it is possible to iterate over a process’s children with

struct task_struct *task;
struct list_head *list;
list_for_each(list, &current->children) {
    task = list_entry(list, struct task_struct, sibling);
    /* task now points to one of current’s children */
}

Also I would be great if somebody explain the list_entry arguments work?

I am having difficult in understanding above code snippet specially list_for_each works.

Have you tried [looking it up](http://lxr.linux.no/linux+v3.12.1/include/linux/list.h#L375)? — Fred Foo, Nov 23 '13 at 17:01
@larsmans yes and also I tried this http://stackoverflow.com/questions/5550404/list-entry-in-linux but still I didn't get it . — user2958183, Nov 23 '13 at 17:09

score 1 · Answer 1 · answered Nov 23 '13 at 19:14

list_for_each is a macro defined as

#define list_for_each(pos, head) \
        for (pos = (head)->next; pos != (head); pos = pos->next)

Since macros in C are expanded by textual substitution, the piece of code you cite becomes

for (list = (&current->children)->next; list != (&current->children); list = list->next) {
    task = list_entry(list, struct task_struct, sibling);
    /* task now points to one of current’s children */
}

This code walks a circular linked list starting at the node (&current->children)->next, until it comes back to (&current->children)->next.

Need clarification on the content given in the Linux Kernel by Robert Love

1 Answers1