Linux Kernel Linked List

Question

I'm trying to use the Linux Kernel Linked List implementation but I am unable to compile. I'm following these sources exactly with no results (http://www.roman10.net/linux-kernel-programminglinked-list/ and http://kernelnewbies.org/FAQ/LinkedLists)

The list.h Kernel Macro for LIST_HEAD_INIT is as follows:

#define LIST_HEAD_INIT(name) { &(name), &(name) }


struct Node {
int data;
struct list_head list;
};

struct Node mylinkedlist;
LIST_HEAD_INIT(&mylinkedlist.list);    

void add(){
struct Node first;
first.data = 1;
first.list = LIST_HEAD_INIT(first.list);
list_add_tail(&first->list, &mylinkedlist.list);
return 0;
}

I keep getting: "error: expected identifier or '(' before '{'"

I have a sneaking suspicion as to what might be going on. Could we see where LIST_HEAD_INIT is defined? — Dennis Meng
– Dennis Meng, Commented Oct 29, 2013 at 0:17
Its defined outside of the function add() right above it. LIST_HEAD_INIT(&mylinkedlist.list). I'm under the impression that it's a Macro in list.h, correct? — Alex
– Alex, Commented Oct 29, 2013 at 0:22
Probably. What I wanted to see was the macro (not where it's used). — Dennis Meng
– Dennis Meng, Commented Oct 29, 2013 at 0:25
oh okay. @DennisMeng: #define LIST_HEAD_INIT(name) { &(name), &(name) } — Alex
– Alex, Commented Oct 29, 2013 at 0:27

moeCake · Accepted Answer · 2013-10-29 01:32:37Z

1

You are getting that wrong.
First, your should LIST_HEAD(mylinkedlist), not LIST_HEAD_INIT nor struct Node mylinkedlist.
mylinkedlist should be a standalone head of kernel linked list struct, it's used to link all list_head.

Second, you should INIT_LIST_HEAD(&first.list), this is the way to dynamically assignment; LIST_HEAD_INIT is used when structure is statically created at compile time.

Last, you should list_add_tail(&first.list, &mylinkedlist).

so the complete code should be:

LIST_HEAD(mylinkedlist);

void add(){
  struct Node first;
  first.data = 1;
  INIT_LIST_HEAD(&first.list);
  list_add_tail(&first.list, &mylinkedlist);
}

this code work fine for me.
I suggest you read Linux Kernel Development chapter 6, it explain this very well.

answered Oct 29, 2013 at 1:32

moeCake

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3 Comments

Alex Over a year ago

I got an error at error: void value not ignored as it out to be at struct Node first = {1, INIT_LIST_HEAD(&first.list)};

moeCake Over a year ago

Are you play another piece of code? if you are statically assign, use LIST_HEAD_INIT.

Blindleistung Over a year ago

Adding link to the kernel-doc: kernel.org/doc/html/v6.0/core-api/…

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