驅動程式 - Linux Device Driver (LDD) - 使用範例 - Assembly (ARM) - Char Device - Class Device


除了使用mknod工具建立Symbloic Link之外，字元驅動程式也可以自行建立這個Symbolic Link

建立步驟： 

1. alloc_chrdev_region()
2. __class_create()
3. device_create()
4. cdev_init()
5. cdev_add()

釋放步驟： 

1. device_destroy()
2. cdev_del()
3. class_destroy()
4. unregister_chrdev_region()

ldd.S

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    .global init_module
    .global cleanup_module
 
    .section .modinfo, "ae"
__UNIQUE_ID_0: .asciz "license=GPL"
__UNIQUE_ID_1: .asciz "author=Steward Fu"
__UNIQUE_ID_2: .asciz "description=Linux Driver"
 
    .equ cdev.kobj,  0
    .equ cdev.owner, 36
    .equ cdev.ops,   40
    .equ cdev.list,  44
    .equ cdev.dev,   52
    .equ cdev.count, 56
 
    .struct 0
cdev_s:
    c0: .struct . + 36
    c1: .struct . + 4
    c2: .struct . + 4
    c3: .struct . + 8
    c4: .struct . + 4
    c5: .struct . + 4
cdev_e:
cdev_l = cdev_e - cdev_s
 
    .equ file_operations.owner,             0
    .equ file_operations.llseek,            4
    .equ file_operations.read,              8
    .equ file_operations.write,             12
    .equ file_operations.read_iter,         16
    .equ file_operations.write_iter,        20
    .equ file_operations.iterate,           24
    .equ file_operations.iterate_shared,    28
    .equ file_operations.poll,              32
    .equ file_operations.unlocked_ioctl,    36
    .equ file_operations.compat_ioctl,      40
    .equ file_operations.mmap,              44
    .equ file_operations.open,              48
    .equ file_operations.flush,             52
    .equ file_operations.release,           56
    .equ file_operations.fsync,             60
    .equ file_operations.fasync,            64
    .equ file_operations.lock,              68
    .equ file_operations.sendpage,          72
    .equ file_operations.get_unmapped_area, 76
    .equ file_operations.check_flags,       80
    .equ file_operations.setfl,             84
    .equ file_operations.flock,             88
    .equ file_operations.splice_write,      92
    .equ file_operations.splice_read,       96
    .equ file_operations.setlease,          100
    .equ file_operations.fallocate,         104
    .equ file_operations.show_fdinfo,       108
    .equ file_operations.mmap_capabilities, 112
    .equ file_operations.copy_file_range,   116
    .equ file_operations.clone_file_range,  120
    .equ file_operations.dedupe_file_range, 124
 
    .struct 0
file_operations_s:
    i0: .struct . + 4
    i1: .struct . + 4
    i2: .struct . + 4
    i3: .struct . + 4
    i4: .struct . + 4
    i5: .struct . + 4
    i6: .struct . + 4
    i7: .struct . + 4
    i8: .struct . + 4
    i9: .struct . + 4
    i10: .struct . + 4
    i11: .struct . + 4
    i12: .struct . + 4
    i13: .struct . + 4
    i14: .struct . + 4
    i15: .struct . + 4
    i16: .struct . + 4
    i17: .struct . + 4
    i18: .struct . + 4
    i19: .struct . + 4
    i20: .struct . + 4
    i21: .struct . + 4
    i22: .struct . + 4
    i23: .struct . + 4
    i24: .struct . + 4
    i25: .struct . + 4
    i26: .struct . + 4
    i27: .struct . + 4
    i28: .struct . + 4
    i29: .struct . + 4
    i30: .struct . + 4
    i31: .struct . + 4
file_operations_e:
file_operations_l = file_operations_e - file_operations_s
 
    .section .data
base:      .dcb 4
mycdev:    .space cdev_l
myfops:    .space file_operations_l
chr_name:  .asciz "myfile"
open_msg:  .asciz "myopen\n"
close_msg: .asciz "myclose\n"
myclass:   .dcb 4
 
    .align 2
    .section .text
myopen:
    push {lr}
    ldr r0, =open_msg
    bl printk
    mov r0, #0
    pop {pc}
 
myclose:
    push {lr}
    ldr r0, =close_msg
    bl printk
    mov r0, #0
    pop {pc}
 
init_module:
    push {r4, r5, lr}
 
    ldr r0, =myfops
    add r1, r0, #file_operations.open
    ldr r2, =myopen
    str r2, [r1]
    add r1, r0, #file_operations.release
    ldr r2, =myclose
    str r2, [r1]
 
    ldr r0, =base
    mov r1, #0
    mov r2, #1
    ldr r3, =chr_name
    bl alloc_chrdev_region
    ldr r4, =base
 
    mov r0, #0
    ldr r1, =chr_name
    ldr r2, =myclass
    bl __class_create
    ldr r1, =myclass
    str r0, [r1]
 
    mov r1, #0
    ldr r2, [r4]
    mov r3, #0
    ldr r5, =chr_name
    push {r5}
    bl device_create
    pop {r5}
 
    ldr r0, =mycdev
    ldr r1, =myfops
    bl cdev_init
 
    ldr r0, =mycdev
    ldr r1, [r4]
    mov r2, #1
    bl cdev_add
 
    mov r0, #0
    pop {r4, r5, pc}
 
cleanup_module:
    push {lr}
    ldr r0, =myclass
    ldr r0, [r0]
    ldr r1, =base
    ldr r1, [r1]
    bl device_destroy
 
    ldr r0, =mycdev
    bl cdev_del
 
    ldr r0, =myclass
    ldr r0, [r0]
    bl class_destroy
 
    ldr r0, =base
    ldr r0, [r0]
    mov r1, #1
    bl unregister_chrdev_region
    pop {pc}
    .end

init_module: 建立字元驅動程式
myopen: 對應User Application的open()
myclose: 對應User Application的close()
cleanup_module: 刪除字元驅動程式

安裝驅動 

# insmod /boot/main.ko

由於使用class device，因此，Symbolic已經建立完成，不再需要使用mknod建立 

# ls -al /dev/myfile
    crw-r--r--    1 root     root      243,   0 Jan  1 00:00 /dev/myfile

開啟裝置 

# echo "" > /dev/myfile
    myopen
    sh: write error: Invalid argument myclose