kernel data structures outline linked list queues maps

kernel data structures

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

singly linked lists

doubly lined lists

circular linked lists

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

usage

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) ({ const typeof( ((type *)0)->member ) *__mptr = (ptr); (type *)( (char *)__mptr - offsetof(type, member) ); })

container_of() #define container_of(ptr, type, member) ({ const typeof( ((type *)0)->member ) *__mptr = (ptr); (type *)( (char *)__mptr - offsetof(type, member) ); }) list_head 0 x. YZ offset = 0 x. YZ 0 x 00

container_of() #define container_of(ptr, type, member) ({ const typeof( ((type *)0)->member ) *__mptr = (ptr); (type *)( (char *)__mptr - offsetof(type, member) ); }) list_head member offset = 0 x. YZ container

offsetof // Keil 8051 compiler #define offsetof(s, m) (size_t)&(((s *)0)->m) // Microsoft x 86 compiler (version 7) #define offsetof(s, m) (size_t)(unsigned long)&(((s *)0)->m) // Diab Coldfire compiler #define offsetof(s, memb) ((size_t)((char *)&((s *)0)->memb-(char *)0)

offsetof in Keil’s C 1. ((s *)0) takes the integer zero and casts it as a pointer to s. 2. ((s *)0)->m dereferences that pointer to point to structure member m. 3. &(((s *)0)->m) computes the address of m. 4. (size_t)&(((s *)0)->m) casts the result to an appropriate data type. reference: http: //blog. linux. org. tw/~jserv/archives/001399. html

functions list_add — add a new entry list_del — deletes entry from 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_for_each_entry — iterate over list of given type

list_entry #define list_entry(ptr, type, member) container_of(ptr, type, member)

QUEUES

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.

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 • •

MAPS

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:

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

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.