Download kernel data structures

kernel data structures
outline
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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
0xYZ
offset = 0xYZ
0x00
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 = 0xYZ
container
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)
// 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
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
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
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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.