"Linux Device Drivers" The 11th Chapter core data type--note

• Basic introduction
  • Because of the Linux multi-platform feature, no matter which important driving force should be portable
  • The core issue associated with kernel code should be access at the same time as the known length of the data item. Capabilities and use of different processors
  • The data types used by the kernel are divided into three main categories
    • Similar to the standard C language type int
    • Similar to u32 this has a definite size type
    • Types like pid_t that are used for specific kernel objects
  • This chapter will discuss under what circumstances these three types are used and how to use
• Use standard C language types
  • When we need a "two-byte shim" or "something in a four-byte string". We cannot use standard types due to different architectures. The size of the normal C language data type is not the same
  • The normal memory address in the kernel is usually unsigned long. On all platforms currently supported by Linux, pointers and long shaping are always the same size
  • The C99 standard defines intptr_t and uintptr_t types, which are shaping variables that can hold pointer values
• Allocate a determined amount of space for a data item
  • <asm/types.h>
  • <linux/types.h>
  • U8, S8
  • U16, S16
  • U32, S32
  • U64, S64
  • Suppose a user-space program needs to use these types, which can be prefixed by a two underscore in front of the name
  • __u8
  • __u32
  • Systems that use the new compiler will support C99 standard types, such as uint8_t and uint32_t

• interface-specific types
  • The most frequently used data types in the kernel are declared by their own typedef. This will prevent any portability issues from occurring.
  • "Interface-specific (interface-specific)" refers to a data type defined by a library to provide an interface for a particular data structure
  • The complete _t type is defined in <linux/types.h>
  • The main problem with _t data items is that it's not easy to choose the right PRINTK or printf output format when we need to print them.
• Other issues related to transplants
  • A common principle is to avoid the use of explicit constant values
  • Time interval
    • When using jiffies to calculate the time interval, you should use Hz to measure
  • Page size
    • The size of the memory page is page_size bytes
    • Page_shift
    • <asm/page.h>
    • GetPageSize Library functions
    • Get_order function
  • byte order
    • <asm/byteorder.h>
      • __big_endian
      • __little_endian
    • U32 cpu_to_le32 (U32);
    • U32 le32_to_cpu (U32);
    • Be64_to_cpu
    • Le16_to_cpus
    • cpu_to_le32p
  • Data alignment
    • <asm/unaligned.h>
      • Get_unaligned (PTR);
      • Put_unaligned (Val, PTR);
  • Pointers and error values
    • Many kernel interfaces return an error message by encoding the error value into a pointer value
    • <linux/err.h>
      • void *err_ptr (long error);
      • Long Is_err (const void *ptr);
      • Long Ptr_err (const void *ptr);
• Linked list
  • <linux/list.h>
    • struct List_head
      • struct List_head *next, *prev;
    • Init_list_head (&list);
    • List_head (list);
    • List_add (struct list_head *new, struct list_head *head);
    • List_add_tail (struct list_head *new, struct list_head *head);
    • List_del (struct list_head *entry);
    • List_del_init (struct list_head *entry);
    • List_move (struct list_head *entry, struct list_head *head);
    • List_move_tail (struct list_head *entry, struct list_head *head);
    • List_empty (struct list_head *head);
    • List_splice (struct list_head *list, struct list_head *head);
    • List_entry (struct List_head *ptr, type_of_struct, field_name);
    • List_for_each (struct list_head *cursor, struct list_head *list)
    • List_for_each_prev (struct list_head *cursor, struct list_head *list)
    • List_for_each_safe (struct list_head *cursor, struct list_head *next, struct list_head *list)
    • List_for_each_entry (type *cursor, struct List_head *list, member)
    • List_for_each_entry_safe (Type *cursor, type *next, struct List_head *list, member)

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"Linux Device Drivers" The 11th Chapter core data type--note