The classical realization of bidirectional linked list in Linux kernel

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The previous chapter "introduces the bidirectional linked list and gives the C/c++/java three kinds of realization", this chapter continues to discuss the two-way link list, introduces the content is the Linux kernel bidirectional link List's classic realization and the usage. It also involves the two classic macro definitions Offsetof and container_of that are very commonly used in the Linux kernel. The content includes:

1. Two classic macro definitions in Linux

2. The classic realization of bidirectional linked list in Linux

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Two classic macro definitions in Linux

If you have checked the Linux kernel source code, then you to Offsetof and container_of these two macros should be not unfamiliar. The two macros were originally written by geeks and later used in the Linux kernel.

1. Offsetof

1.1 Offsetof Introduction

Definition: Offsetof is defined in the include/linux/stddef.h of the Linux kernel.

#define OFFSETOF (Type, member) ((size_t) & ((type *) 0)->member)

description : Gets the offset of the variable members (member) of the struct body (TYPE) in this structure.

(TYPE *) 0) converts 0 to a type pointer, that is, the address of the type's pointer is 0.

(TYPE *) 0)->member access to data members in the structure.

(0) & ((TYPE *)->member) Remove the address of the data member. Because the address of type is 0, the address obtained here is the offset of the relative member in type.

(size_t) (& (((type*) 0)->member) result conversion type. For 32-bit systems, the size_t is the unsigned int type, and for 64-bit systems, size_t is the unsigned long type.

1.2 Offsetof Sample

Code (OFFSET_TEST.C)

 1 #include <stdio.h>
 2 
 3//Get the offset of the variable members (member) of the struct body (TYPE) in this structure.
 4 #define OFFSETOF (type, member) ((size_t) & ((type *) 0)->member)
 5 
 6 struct student
 7 {
 8< C8/>char gender;
 9     int id;     int age;
One     char name[20];
; 
void Main ()     int gender_offset, Id_offset, Age_offset, Name_offset;     gender_offset = offsetof (struct student, gender);     id_offset = offsetof (struct student, id);     age_offset = offsetof (struct student, age);     name_offset = offsetof (struct student, name);     printf ("Gender_offset =%d\n", gender_offset);     printf ("Id_offset =%d\n", id_offset);     printf ("Age_offset =%d\n", age_offset);
Num     printf ("Name_offset =%d\n", name_offset);
27}