Linked List : list_replace
=============================
.. tab-set::
.. tab-item:: Linked List : list_replace
* In this program, you are going to learn
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* How to delete from one list and add as another's head ?
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* How to use the below API's ?
* `INIT_LIST_HEAD <https://elixir.bootlin.com/linux/v6.2/source/tools/include/linux/list.h#L25>`_
* `list_add <https://elixir.bootlin.com/linux/latest/source/include/linux/list.h#L86>`_
* `list_for_each_entry <https://elixir.bootlin.com/linux/v6.2/source/include/linux/list.h#L673>`_
* `list_replace <https://elixir.bootlin.com/linux/latest/source/tools/include/linux/list.h#L125>`_
* `list_for_each_entry_safe <https://elixir.bootlin.com/linux/v6.2/source/tools/include/linux/list.h#L531>`_
* `list_del <https://elixir.bootlin.com/linux/v6.2/source/tools/include/linux/list.h#L113>`_
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Topics in this section,
* :ref:`Explanation of Program part by part <list_replace_4>`
* :ref:`List of headers <list_replace_5>`
* :ref:`Modules macro <list_replace_6>`
* :ref:`Initialize function and variables <list_replace_7>`
* :ref:`Module init function <list_replace_8>`
* :ref:`Module exit function <list_replace_9>`
* :ref:`Mention init and exit function <list_replace_11>`
* :ref:`See the full program below <list_replace_0>`
* :ref:`Makefile <list_replace_1>`
* :ref:`Compile and Load <list_replace_2>`
* :ref:`Summary of Linked List APIs <list_replace_3>`
.. _list_replace_4:
.. tab-set::
.. tab-item:: Explanation of program part by part
* In this example, we are going to replace old entry by new one.
.. _list_replace_5:
.. tab-set::
.. tab-item:: List of headers
* Add the list of header files to refer the APIs used in this program.
.. code-block:: c
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/slab.h>
.. _list_replace_6:
.. tab-set::
.. tab-item:: Modules macro
* Add the modules macro which lists the information about the license, author and description.
.. code-block:: c
MODULE_LICENSE("GPL");
MODULE_AUTHOR("linux_usr");
MODULE_DESCRIPTION("Linked List");
.. _list_replace_7:
.. tab-set::
.. tab-item:: Initialize function and variables
* ``LIST_HEAD`` is used to initialize the list.
.. code-block:: c
struct list_node {
int data;
struct list_head list;
};
static LIST_HEAD(my_list);
static LIST_HEAD(new_list);
struct list_node data1, data2, data3,data4, *entry;
.. _list_replace_8:
.. tab-set::
.. tab-item:: Module init function
* Add the module init function to execute the function once when the module is loaded to the linux kernel.
.. code-block:: c
static int __init linkedlist_init(void)
{
pr_info("Driver loaded\n");
data1.data = 10;
data2.data = 20;
data3.data = 30;
data4.data = 40;
INIT_LIST_HEAD(&data1.list);
INIT_LIST_HEAD(&data2.list);
INIT_LIST_HEAD(&data3.list);
INIT_LIST_HEAD(&data4.list);
list_add(&data1.list, &my_list);
list_add(&data2.list, &my_list);
list_add(&data3.list, &my_list);
list_add(&data4.list, &my_list);
list_for_each_entry(entry, &my_list, list)
printk(KERN_INFO "my_list entry 1: %d\n",entry->data);
list_replace(&data3.list, &data5.list);
list_for_each_entry(entry, &my_list, list)
printk(KERN_INFO "my_list entry 2: %d\n",entry->data);
return 0;
}
* ``INIT_LIST_HEAD`` is used to initialize a list_head structure.
.. code-block:: c
INIT_LIST_HEAD(&data1.list);
INIT_LIST_HEAD(&data2.list);
INIT_LIST_HEAD(&data3.list);
INIT_LIST_HEAD(&data4.list);
* ``list_add`` to insert a new element after the given list head.
.. code-block:: c
list_add(&data1.list, &my_list);
list_add(&data2.list, &my_list);
list_add(&data3.list, &my_list);
list_add(&data4.list, &my_list);
* ``list_replace`` to replace old entry by new one.
.. code-block:: c
list_replace(&data3.list, &data5.list);
.. _list_replace_9:
.. tab-set::
.. tab-item:: Module exit function
* Add module exit function which is executed once the module is unloaded from the kernel.
.. code-block:: c
static void __exit linkedlist_exit(void)
{
struct list_node *ptr, *next;
list_for_each_entry_safe(ptr, next, &my_list, list) {
list_del(&ptr->list);
}
list_for_each_entry_safe(ptr, next, &new_list, list) {
list_del(&ptr->list);
}
pr_info("Driver unloaded\n");
}
.. _list_replace_11:
.. tab-set::
.. tab-item:: Mention init and exit functions
* Add the module init and exit which is called when the module is loaded and unloaded.
.. code-block:: c
module_init(linkedlist_init);
module_exit(linkedlist_exit);
.. _list_replace_0:
.. tab-set::
.. tab-item:: See the full program below
.. tab-set::
.. tab-item:: linked_list.c
.. literalinclude:: list_replace/linked_list.c
:language: c
:linenos:
.. _list_replace_1:
.. tab-set::
.. tab-item:: Makefile
.. literalinclude:: list_replace/Makefile
:language: c
:linenos:
.. _list_replace_2:
.. tab-set::
.. tab-item:: Compile and Load
* Run Make to compile the module.
.. code-block:: shell
$make
make -C /lib/modules/5.4.0-150-generic/build M=$HOME/kernel_linked_list modules
make[1]: Entering directory '/usr/src/linux-headers-5.4.0-150-generic'
CC [M] $HOME/kernel_linked_list/linked_list.o
Building modules, stage 2.
MODPOST 1 modules
CC [M] $HOME/kernel_linked_list/linked_list.mod.o
LD [M] $HOME/kernel_linked_list/linked_list.ko
make[1]: Leaving directory '/usr/src/linux-headers-5.4.0-150-generic'
* Run ls to check if linked_list.ko is generated or not.
.. code-block:: shell
$ ls -l
total 36
-rw-rw-r-- 1 test test 154 Feb 26 13:18 Makefile
-rw-rw-r-- 1 test test 47 Feb 26 13:18 modules.order
-rw-rw-r-- 1 test test 0 Feb 26 13:18 Module.symvers
-rw-rw-r-- 1 test test 820 Feb 26 13:18 linked_list.c
-rw-rw-r-- 1 test test 5880 Feb 26 13:18 linked_list.ko
-rw-rw-r-- 1 test test 47 Feb 26 13:18 linked_list.mod
-rw-rw-r-- 1 test test 919 Feb 26 13:18 linked_list.mod.c
-rw-rw-r-- 1 test test 3448 Feb 26 13:18 linked_list.mod.o
-rw-rw-r-- 1 test test 3320 Feb 26 13:18 linked_list.o
* Run insmod to load the module.
.. code-block:: shell
$ sudo insmod ./linked_list.ko
* Check the kernel messages to see if the kernel module is loaded or not.
.. code-block:: shell
$ dmesg
[ 537.955566] driver loaded
[ 537.955568] my_list entry 1: 40
[ 537.955568] my_list entry 1: 30
[ 537.955569] my_list entry 1: 20
[ 537.955569] my_list entry 1: 10
[ 537.955569] my_list entry 2: 40
[ 537.955569] my_list entry 2: 50
[ 537.955570] my_list entry 2: 20
[ 537.955570] my_list entry 2: 10
* Run rmmod to unload the module.
.. code-block:: shell
$ sudo rmmod linked_list
* Check dmesg to see if the module is unloaded from kernel.
.. code-block:: shell
$ dmesg
[ 537.955566] driver loaded
[ 537.955568] my_list entry 1: 40
[ 537.955568] my_list entry 1: 30
[ 537.955569] my_list entry 1: 20
[ 537.955569] my_list entry 1: 10
[ 537.955569] my_list entry 2: 40
[ 537.955569] my_list entry 2: 50
[ 537.955570] my_list entry 2: 20
[ 537.955570] my_list entry 2: 10
[ 541.931631] Driver unloaded
.. _list_replace_3:
.. tab-set::
.. tab-item:: Summary
=============================== =====================================================================
API Learning
=============================== =====================================================================
INIT_LIST_HEAD To initialize a list_head structure
LIST_HEAD To initialize the list
list_for_each_entry To iterate over list of given type
list_add To insert a new entry after the specified head
list_for_each_entry_safe To iterate over list of given type safe against removal of list entry
list_del To delete entry from list
list_replace To replace old entry by new one
=============================== =====================================================================
.. card:: See Also
* Previous Chapters
* :doc:`../chapter1_basics/chapter1_basics`
* :doc:`../chapter2_kthreads/chapter2_kthreads`
* :doc:`../chapter3_tasklets/chapter3_tasklets`
* :doc:`../chapter4_workqueue/chapter4_workqueue`
* :doc:`../chapter5_timer/chapter5_timer`
* Other Linked List topics
* :doc:`insert_rear`
* :doc:`insert_at_pos`
* :doc:`delete_rear`
* :doc:`delete_front`
* :doc:`delete_at_pos`
* :doc:`list_splice`
* :doc:`list_splice_init`
* :doc:`list_splice_tail`
* :doc:`list_splice_tail_init`
* :doc:`list_cut_position`
* :doc:`list_del_init`
* :doc:`list_first`
* :doc:`list_first_entry_or_null`
* :doc:`list_for_each`
* :doc:`list_for_each_entry_continue`
* :doc:`list_for_each_entry_continue_reverse`
* :doc:`list_for_each_entry_safe_reverse`
* :doc:`list_is_singular`
* :doc:`list_last`
* :doc:`list_move`
* :doc:`list_move_tail`
* :doc:`list_replace`
* :doc:`list_replace_init`
* Next Chapter
* :doc:`../chapter9_fileSystem/chapter9_fileSystem`
* Other Chapter
* :doc:`../chapter10_netlink/chapter10_netlink`