kernel data structures

1. kernel data structures

2. outline • linked list • queues • maps • binary trees • algorithmic complexity

3. singly linked lists

4. doubly lined lists

5. circular linked lists

6. the Linux kernel’s implementation • The linked-list code is declared in the header file <linux/list.h> and the data structure is simple

7. usage

8. container_of() • Using the macro container_of() , we can easily find the parent structure containing any given member variable. #define container_of(ptr, type, member) ({ \ consttypeof( ((type *)0)->member ) *__mptr = (ptr); \ (type *)( (char *)__mptr - offsetof(type,member) );})

9. container_of() #define container_of(ptr, type, member) ({ \ consttypeof( ((type *)0)->member ) *__mptr = (ptr); \ (type *)( (char *)__mptr - offsetof(type,member) );}) list_head 0xYZ offset = 0xYZ 0x00

10. container_of() #define container_of(ptr, type, member) ({ \ consttypeof( ((type *)0)->member ) *__mptr = (ptr); \ (type *)( (char *)__mptr - offsetof(type,member) );}) list_head member offset = 0xYZ container

11. offsetof // Keil 8051 compiler#define offsetof(s,m) (size_t)&(((s *)0)->m)// Microsoft x86 compiler (version 7)#define offsetof(s,m) (size_t)(unsigned long)&(((s *)0)->m)// DiabColdfire compiler#define offsetof(s,memb) ((size_t)((char *)&((s *)0)->memb-(char *)0)

12. offsetof in Keil’s C • ((s *)0) takes the integer zero and casts it as a pointer to s. • ((s *)0)->m dereferences that pointer to point to structure member m. • &(((s *)0)->m) computes the address of m. • (size_t)&(((s *)0)->m) casts the result to an appropriate data type. reference: http://blog.linux.org.tw/~jserv/archives/001399.html

13. functions list_add — add a new entry list_del— deletes entry from list list_move— delete from one list and add as another's head list_empty— tests whether a list is empty list_entry— get the struct for this entry list_for_each— iterate over a list list_for_each_entry— iterate over list of given type

14. list_entry #define list_entry(ptr, type, member) \ container_of(ptr, type, member)

15. queues

16. kfifo • Linux’s kfifo works like most other queue abstractions, providing two primary operations: • enqueue (unfortunately named in ) and • dequeue(out ). • The kfifo object maintains two offsets into the queue: an in offset and an out offset. • The enqueue (in) operation copies data into the queue, starting at the in offset.

17. functions • kfifo_reset— removes the entire FIFO contents • kfifo_put— puts some data into the FIFO • kfifo_get— gets some data from the FIFO • kfifo_len— returns the number of bytes available in the FIFO • kfifo_init— allocates a new FIFO using a preallocated buffer • kfifo_alloc— allocates a new FIFO and its internal buffer • kfifo_free— frees the FIFO

18. maps

19. definition • A map , also known as an associative array , is a collection of unique keys, where each key is associated with a specific value. • The relationship between a key and its value is called a mapping . • Maps support at least three operations:

20. definition: operator • Add (key, value) • Remove (key) • value = Lookup (key)

21. implementation • The Linux kernel provides a simple and efficient map data structure, but it is not a general-purpose map • It is designed for one specific use case: mapping a unique identification number (UID) to a pointer.