Makefile
# disable/enable debugging
#DEBUG = y
# 当DEBUG变量等于y时。两个比较变量用括号括起来，逗号分隔。ifeq和括号中间有一个空格。
ifeq ($(DEBUG), y)
# += 追加变量值。如果该变量之前没有被定义过，+=就自动变成=，变量被定义成递归展开式的变量；如果之前已经定义过，就遵循之前的风格。
# = 递归展开式变量：在定义时，变量中对其它变量的引用不会被替换展开。变量在引用它的地方被替换展开时，变量中其它变量才被同时替换展开。
# -O 程序优化参数；
# -g 使生成的debuginfo包额外支持gnu和gdb调试程序，易于使用
# -DSCULL_DEBUG 即define SCULL_DEBUG TODO
DEBFLAGS += -O -g -DSCULL_DEBUG # -O is needed to expand inlines
else
DEBFLAGS += -O2
endif
# CFLAGS影响编译过程。应在遵循原设置的基础上添加新的设置，注意+=
CFLAGS += $(DEBFLAGS)
# -I 选项指出头文件位置。LDDINC是下面定义的一个变量。
CFLAGS += -I$(LDDINC)
# 如果KERNELRELEASE不等于空。ifneq判断参数是否不相等。
ifneq ($(KERNELRELEASE),)
# := 直接展开式变量：在定义时就展开变量中对其它变量或函数的引用，定以后就成了需要定义的文本串。不能实现对其后定义变量的引用。
scull-objs := main.o pipe.o access.o
obj-m := scull.o
# 否则（KERNELRELEASE是空）
else
# ?= 条件赋值：只有在此变量之前没有赋值的情况下才会被赋值。
# shell uname r 内核版本号
KERNELDIR ?= /lib/modules/$(shell uname r)/build
# shell pwd 当前在文件系统中的路径
PWD := $(shell pwd)
modules:
# $(MAKE) TODO
# -C $(KERNELDIR) 在读取Makefile之前进入$(KERNELDIR)目录
# M=$(PWD) LDDINC=$(PWD)/../include 传递2个变量给Makefile
# modules 是$(KERNELDIR)中的Makefile的target TODO
$(MAKE) -C $(KERNELDIR) M=$(PWD) LDDINC=$(PWD)/../include modules
endif
# 清理
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions
# TODO
# 产生依赖信息文件，如果存在的话则将其包含到Makefile中。
depend .depend dep:
$(CC) $(CFLAGS) -M *.c > .depend
ifeq (.depend,$(wildcard .depend))
include .depend
endif
---
参考
1.[GNU make中文手册]
2.[CFLAGS 统一和 gcc 3.4] http://www.magiclinux.org/node/821
3.[LDD3源码学习笔记之scull_main] http://www.sudu.cn/info/html/edu/20070101/291462.html
4.http://topic.csdn.net/u/20070815/22/cbd2f64d-f6e3-4938-97f8-4f8fe5a21465.html
scull.h
/*
* scull.h -- definitions for the char module
*
* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
* Copyright (C) 2001 O'Reilly & Associates
*
* The source code in this file can be freely used, adapted,
* and redistributed in source or binary form, so long as an
* acknowledgment appears in derived source files. The citation
* should list that the code comes from the book "Linux Device
* Drivers" by Alessandro Rubini and Jonathan Corbet, published
* by O'Reilly & Associates. No warranty is attached;
* we cannot take responsibility for errors or fitness for use.
*
* $Id: scull.h,v 1.15 2004/11/04 17:51:18 rubini Exp $
*/
#ifndef _SCULL_H_
#define _SCULL_H_
#include <linux/ioctl.h> /* needed for the _IOW etc stuff used later */
/*
* Macros to help debugging
*/
// undef取消以前定义的宏
#undef PDEBUG /* undef it, just in case */
#ifdef SCULL_DEBUG
# ifdef __KERNEL__
// 内核空间，printk 输出调试信息
/* This one if debugging is on, and kernel space */
# define PDEBUG(fmt, args
) printk( KERN_DEBUG "scull: " fmt, ## args)
# else
// 用户空间，fprintf 输出调试信息
/* This one for user space */
# define PDEBUG(fmt, args) fprintf(stderr, fmt, ## args)
# endif
#else
# define PDEBUG(fmt, args) /* not debugging: nothing */
#endif
#undef PDEBUGG
#define PDEBUGG(fmt, args) /* nothing: it's a placeholder */
#ifndef SCULL_MAJOR
// 主设备号指定为0，表示由内核动态分配
#define SCULL_MAJOR 0 /* dynamic major by default */
#endif
// bare device的数量，也就是要请求的连续设备编号的总数
#ifndef SCULL_NR_DEVS
#define SCULL_NR_DEVS 4 /* scull0 through scull3 */
#endif
// TODO
#ifndef SCULL_P_NR_DEVS
#define SCULL_P_NR_DEVS 4 /* scullpipe0 through scullpipe3 */
#endif
/*
* The bare device is a variable-length region of memory.
* Use a linked list of indirect blocks.
*
* "scull_dev->data" points to an array of pointers, each
* pointer refers to a memory area of SCULL_QUANTUM bytes.
*
* The array (quantum-set) is SCULL_QSET long.
*/
// 每个内存区字节数。（量子长度）
#ifndef SCULL_QUANTUM
#define SCULL_QUANTUM 4000
#endif
// 数组长度（量子集长度）
#ifndef SCULL_QSET
#define SCULL_QSET 1000
#endif
/*
* The pipe device is a simple circular buffer. Here its default size
*/
// 管道设备，环形缓冲大小。
#ifndef SCULL_P_BUFFER
#define SCULL_P_BUFFER 4000
#endif
/*
* Representation of scull quantum sets.
*/
struct scull_qset {
void **data;
struct scull_qset *next;
};
// 使用scull_dev表示每个设备
struct scull_dev {
struct scull_qset *data; /* Pointer to first quantum set */
int quantum; /* the current quantum size */
int qset; /* the current array size */
unsigned long size; /* amount of data stored here */
unsigned int access_key; /* used by sculluid and scullpriv */
struct semaphore sem; /* mutual exclusion semaphore */
struct cdev cdev; /* Char device structure */
};
// TODO 什么用？
/*
* Split minors in two parts
*/
// 高四位
#define TYPE(minor) (((minor) >> 4) & 0xf) /* high nibble */
// 低四位
#define NUM(minor) ((minor) & 0xf) /* low nibble */
/*
* The different configurable parameters
*/
extern int scull_major; /* main.c */
extern int scull_nr_devs;
extern int scull_quantum;
extern int scull_qset;
extern int scull_p_buffer; /* pipe.c */
/*
* Prototypes for shared functions
*/
int scull_p_init(dev_t dev);
void scull_p_cleanup(void);
int scull_access_init(dev_t dev);
void scull_access_cleanup(void);
int scull_trim(struct scull_dev *dev);
ssize_t scull_read(struct file *filp, char __user *buf, size_t count,
loff_t *f_pos);
ssize_t scull_write(struct file *filp, const char __user *buf, size_t count,
loff_t *f_pos);
loff_t scull_llseek(struct file *filp, loff_t off, int whence);
int scull_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd, unsigned long arg);
/*
* Ioctl definitions
*/
// TODO 魔数什么用？
/* Use 'k' as magic number */
#define SCULL_IOC_MAGIC 'k'
/* Please use a different 8-bit number in your code */
#define SCULL_IOCRESET _IO(SCULL_IOC_MAGIC, 0)
/*
* S means "Set" through a ptr,
* T means "Tell" directly with the argument value
* G means "Get": reply by setting through a pointer
* Q means "Query": response is on the return value
* X means "eXchange": switch G and S atomically
* H means "sHift": switch T and Q atomically
*/
#define SCULL_IOCSQUANTUM _IOW(SCULL_IOC_MAGIC, 1, int)
#define SCULL_IOCSQSET _IOW(SCULL_IOC_MAGIC, 2, int)
#define SCULL_IOCTQUANTUM _IO(SCULL_IOC_MAGIC, 3)
#define SCULL_IOCTQSET _IO(SCULL_IOC_MAGIC, 4)
#define SCULL_IOCGQUANTUM _IOR(SCULL_IOC_MAGIC, 5, int)
#define SCULL_IOCGQSET _IOR(SCULL_IOC_MAGIC, 6, int)
#define SCULL_IOCQQUANTUM _IO(SCULL_IOC_MAGIC, 7)
#define SCULL_IOCQQSET _IO(SCULL_IOC_MAGIC, 8)
#define SCULL_IOCXQUANTUM _IOWR(SCULL_IOC_MAGIC, 9, int)
#define SCULL_IOCXQSET _IOWR(SCULL_IOC_MAGIC,10, int)
#define SCULL_IOCHQUANTUM _IO(SCULL_IOC_MAGIC, 11)
#define SCULL_IOCHQSET _IO(SCULL_IOC_MAGIC, 12)
/*
* The other entities only have "Tell" and "Query", because they're
* not printed in the book, and there's no need to have all six.
* (The previous stuff was only there to show different ways to do it.
*/
#define SCULL_P_IOCTSIZE _IO(SCULL_IOC_MAGIC, 13)
#define SCULL_P_IOCQSIZE _IO(SCULL_IOC_MAGIC, 14)
/* more to come */
#define SCULL_IOC_MAXNR 14
#endif /* _SCULL_H_ */
main.c
/*
* main.c -- the bare scull char module
*
* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
* Copyright (C) 2001 O'Reilly & Associates
*
* The source code in this file can be freely used, adapted,
* and redistributed in source or binary form, so long as an
* acknowledgment appears in derived source files. The citation
* should list that the code comes from the book "Linux Device
* Drivers" by Alessandro Rubini and Jonathan Corbet, published
* by O'Reilly & Associates. No warranty is attached;
* we cannot take responsibility for errors or fitness for use.
*
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <linux/seq_file.h>
#include <linux/cdev.h>
#include <asm/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_*_user */
#include "scull.h" /* local definitions */
/*
* Our parameters which can be set at load time.
*/
int scull_major = SCULL_MAJOR; // 主设备号
int scull_minor = 0; // 次设备号
int scull_nr_devs = SCULL_NR_DEVS; /* number of bare scull devices */
int scull_quantum = SCULL_QUANTUM; // 量子大小（字节）
int scull_qset = SCULL_QSET; // 量子集大小
// 插入模块时指定的参数
module_param(scull_major, int, S_IRUGO);
module_param(scull_minor, int, S_IRUGO);
module_param(scull_nr_devs, int, S_IRUGO);
module_param(scull_quantum, int, S_IRUGO);
module_param(scull_qset, int, S_IRUGO);
MODULE_AUTHOR("Alessandro Rubini, Jonathan Corbet");
MODULE_LICENSE("Dual BSD/GPL");
struct scull_dev *scull_devices; /* allocated in scull_init_module */
// 释放整个数据区。简单遍历列表并且释放它发现的任何量子和量子集。
// 在scull_open 在文件为写而打开时调用。
// 调用这个函数时必须持有信号量。
/*
* Empty out the scull device; must be called with the device
* semaphore held.
*/
int scull_trim(struct scull_dev *dev)
{
struct scull_qset *next, *dptr;
int qset = dev->qset; /* "dev" is not-null */ // 量子集大小
int i;
// 遍历多个量子集。dev->data 指向第一个量子集。
for (dptr = dev->data; dptr; dptr = next) { /* all the list items */
if (dptr->data) { // 量子集中有数据
for (i = 0; i < qset; i++) // 遍历释放当前量子集中的每个量子。量子集大小为qset。
kfree(dptr->data[i]);
kfree(dptr->data); // 释放量子指针数组
dptr->data = NULL;
}
// next获取下一个量子集，释放当前量子集。
next = dptr->next;
kfree(dptr);
}
// 清理struct scull_dev dev中变量的值
dev->size = 0;
dev->quantum = scull_quantum;
dev->qset = scull_qset;
dev->data = NULL;
return 0;
}
#ifdef SCULL_DEBUG /* use proc only if debugging */
/*
* The proc filesystem: function to read and entry
*/
// 在proc里实现文件，在文件被读时产生数据
// 当一个进程读 /proc 文件，内核分配了一页内存，驱动可以写入数据返回用户空间
int scull_read_procmem(char *buf, // 写数据的缓冲区
char **start, // 数据写在页中的哪里
off_t offset,
int count,
int *eof, // 必须被驱动设置，表示写数据结束
void *data) // data传递私有数据
{
int i, j, len = 0;
int limit = count - 80; /* Don't print more than this */
// 遍历每个设备，输出总字节数小于limit
for (i = 0; i < scull_nr_devs && len <= limit; i++) {
struct scull_dev *d = &scull_devices[i];
struct scull_qset *qs = d->data;
if (down_interruptible(&d->sem))
return -ERESTARTSYS;
len += sprintf(buf+len,"\nDevice %i: qset %i, q %i, sz %li\n", // 输出当前是第几个scull设备，量子集大小，量子大小，设备大小
i, d->qset, d->quantum, d->size);
// 遍历当前设备的每个量子集
for (; qs && len <= limit; qs = qs->next) { /* scan the list */
len += sprintf(buf + len, " item at %p, qset at %p\n", // 输出当前量子集 和 量子集中的数据 在内存中的位置。
qs, qs->data);
// 输出最后一个量子集中，每个量子的地址
if (qs->data && !qs->next) /* dump only the last item */
for (j = 0; j < d->qset; j++) {
if (qs->data[j])
len += sprintf(buf + len,
" % 4i: %8p\n",
j, qs->data[j]);
}
}
up(&scull_devices[i].sem);
}
*eof = 1;
return len;
}
/// seq_file接口：创建一个虚拟文件，遍历一串数据，这些数据必须返回用户空间。
// 步骤：start, next, stop, show
/*
* For now, the seq_file implementation will exist in parallel. The
* older read_procmem function should maybe go away, though.
*/
/*
* Here are our sequence iteration methods. Our "position" is
* simply the device number.
*/
// 参数：*s总被忽略；pos指从哪儿开始读，具体意义依赖于实现。
// seq_file典型的实现是遍历一感兴趣的数据序列，pos就用来指示序列中的下一个元素。
// 在scull中，pos简单地作为scull_array数组的索引。
static void *scull_seq_start(struct seq_file *s, loff_t *pos)
{
if (*pos >= scull_nr_devs)
return NULL; /* No more to read */
return scull_devices + *pos; // 返回索引号是pos的scull设备
}
// 返回下一个scull设备
static void *scull_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
(*pos)++;
if (*pos >= scull_nr_devs)
return NULL;
return scull_devices + *pos;
}
static void scull_seq_stop(struct seq_file *s, void *v)
{
/* Actually, there's nothing to do here */
}
// 输出迭代器v生成的数据到用户空间
static int scull_seq_show(struct seq_file *s, void *v)
{
struct scull_dev *dev = (struct scull_dev *) v;
struct scull_qset *d;
int i;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
seq_printf(s, "\nDevice %i: qset %i, q %i, sz %li\n", // 输出，相当于用于空间的printf。返回非0值表示缓冲区满，超出的数据被丢弃。
(int) (dev - scull_devices), dev->qset,
dev->quantum, dev->size);
// 遍历设备的每一个量子集
for (d = dev->data; d; d = d->next) { /* scan the list */
seq_printf(s, " item at %p, qset at %p\n", d, d->data); // 量子集地址，量子集中数据地址
// 输出最后一个量子集中，每个量子的地址
if (d->data && !d->next) /* dump only the last item */
for (i = 0; i < dev->qset; i++) {
if (d->data[i])
seq_printf(s, " % 4i: %8p\n",
i, d->data[i]);
}
}
up(&dev->sem);
return 0;
}
// seq_file的操作集
/*
* Tie the sequence operators up.
*/
static struct seq_operations scull_seq_ops = {
.start = scull_seq_start,
.next = scull_seq_next,
.stop = scull_seq_stop,
.show = scull_seq_show
};
// 打开 /proc 文件。在这里也就是初始化seq_file
/*
* Now to implement the /proc file we need only make an open
* method which sets up the sequence operators.
*/
static int scull_proc_open(struct inode *inode, struct file *file)
{
return seq_open(file, &scull_seq_ops); // 连接file和seq_file
}
// proc文件的操作集
/*
* Create a set of file operations for our proc file.
*/
static struct file_operations scull_proc_ops = {
.owner = THIS_MODULE,
.open = scull_proc_open,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release
};
/*
* Actually create (and remove) the /proc file(s).
*/
// 建立通过proc方式debug时需要的proc文件
static void scull_create_proc(void)
{
struct proc_dir_entry *entry;
//TODO 创建了两个文件?
// 创建文件scullmem并使之关联read函数
create_proc_read_entry("scullmem", // name:要创建的文件名
0 /* default mode */, // mode:文件掩码，为0则按照系统默认的掩码创建文件
NULL /* parent dir */, // base:指定文件所在目录，为NULL则被创建在/proc根目录下
scull_read_procmem, // read_proc:处理读请求的回调函数
NULL /* client data */); // 内核忽略此参数，但会把它当做参数传递给read_proc
entry = create_proc_entry("scullseq", 0, NULL); // 参数:名字，掩码，父目录
// create_proc_entry 同样用来建立/proc文件，但较create_proc_read_entry 更为底层一些
if (entry)
entry->proc_fops = &scull_proc_ops;
}
// 移除创建的 /proc 文件
static void scull_remove_proc(void)
{
/* no problem if it was not registered */
// 移除一个proc_dir_entry, 如果这个结构还在使用，设置deleted标志，返回
remove_proc_entry("scullmem", // const char *name
NULL /* parent dir */); // struct proc_dir_entry *parent
remove_proc_entry("scullseq", NULL);
}
#endif /* SCULL_DEBUG */
/*
* Open and close
*/
/// 打开设备:文件私有数据，设置成对应的scull_dev
int scull_open(struct inode *inode, struct file *filp)
{
struct scull_dev *dev; /* device information */
dev = container_of(inode->i_cdev, struct scull_dev, cdev);
filp->private_data = dev; /* for other methods */
/* now trim to 0 the length of the device if open was write-only */
/// 文件以只读模式打开时，截断为0
if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) {
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
scull_trim(dev); /* ignore errors */
up(&dev->sem);
}
return 0; /* success */
}
// file_operations 中的.release
int scull_release(struct inode *inode, struct file *filp)
{
return 0;
}
/*
* Follow the list
*/
// 返回设备dev的第n个量子集，量子集不够n个就申请新的。
struct scull_qset *scull_follow(struct scull_dev *dev, int n)
{
struct scull_qset *qs = dev->data; // 当前设备的量子集
/* Allocate first qset explicitly if need be */
// 如果当前设备还没有量子集，就显式分配第一个量子集
if (! qs) {
// kmalloc 内核模块中，动态分配连续的物理地址，用于小内存分配
qs = dev->data = kmalloc(sizeof(struct scull_qset), // size_t size. 要分配的块的大小
GFP_KERNEL); // int flags. GFP_KERNEL 在当前进程缺少内存时，可以睡眠来等待一页。 TODO
// 使用 GFP_KERNEL 来分配内存的函数，必须可重入 且不能在原子上下文中运行。
if (qs == NULL)
return NULL; /* Never mind */
memset(qs, 0, sizeof(struct scull_qset));
}
/* Then follow the list */
// 遍历当前设备的量子集链表n步，量子集不够就申请新的。
while (n--) {
if (!qs->next) {
qs->next = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
if (qs->next == NULL) // 不关心内存分配失败? TODO
return NULL; /* Never mind */
memset(qs->next, 0, sizeof(struct scull_qset));
}
qs = qs->next;
continue;
}
return qs;
}
/*
* Data management: read and write
*/
ssize_t scull_read(struct file *filp, // 设备对应的文件结构
char __user *buf, // 读到用户空间
size_t count, // 字节数
loff_t *f_pos) // 要读的位置，在filp私有数据中的偏移
{
struct scull_dev *dev = filp->private_data;
struct scull_qset *dptr; /* the first listitem */
int quantum = dev->quantum, qset = dev->qset; // 量子、量子集大小
int itemsize = quantum * qset; /* how many bytes in the listitem */ // 一个量子集的字节数
int item, s_pos, q_pos, rest;
ssize_t retval = 0;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
if (*f_pos >= dev->size)
goto out;
// 要读的count超出了size，裁断count
if (*f_pos + count > dev->size)
count = dev->size - *f_pos;
/* find listitem, qset index, and offset in the quantum */
// 在量子/量子集中定位读写位置:第几个量子集，中的 第几个量子，在量子中的偏移
item = (long)*f_pos / itemsize; // 第几个量子集
rest = (long)*f_pos % itemsize; // 在量子集中的偏移量
s_pos = rest / quantum; q_pos = rest % quantum; // 第几个量子；在量子中的偏移
/* follow the list up to the right position (defined elsewhere) */
// 获取要读的量子集指针
dptr = scull_follow(dev, item);
if (dptr == NULL || !dptr->data || ! dptr->data[s_pos]) // 没有量子集，量子集中没有data，没有第s_pos个量子
goto out; /* don't fill holes */
/* read only up to the end of this quantum */
// 只在一个量子中读:如果count超出当前量子，截断count
if (count > quantum - q_pos)
count = quantum - q_pos;
// 将读位置的内容复制到用户空间buf，共复制count字节
if (copy_to_user(buf, // void __user *to
dptr->data[s_pos] + q_pos, // const void *from
count)) { // unsigned long n
retval = -EFAULT;
goto out;
}
*f_pos += count;
retval = count;
out:
up(&dev->sem);
return retval;
}
ssize_t scull_write(struct file *filp, // 设备对应的文件结构
const char __user *buf,
size_t count,
loff_t *f_pos)
{
struct scull_dev *dev = filp->private_data;
struct scull_qset *dptr;
int quantum = dev->quantum, qset = dev->qset; // 量子、量子集大小
int itemsize = quantum * qset; // 一个量子集的字节数
int item, s_pos, q_pos, rest;
ssize_t retval = -ENOMEM; /* value used in "goto out" statements */
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
/* find listitem, qset index and offset in the quantum */
// 查找量子集，在量子集中的索引，和在量子中的偏移
item = (long)*f_pos / itemsize;
rest = (long)*f_pos % itemsize;
s_pos = rest / quantum; q_pos = rest % quantum;
// 获取要写入数据的量子集
/* follow the list up to the right position */
dptr = scull_follow(dev, item); // 获取设备dev的第item个量子集
if (dptr == NULL)
goto out;
// 如果该量子集数据是NULL，就申请一块新内存
if (!dptr->data) {
dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL);
if (!dptr->data)
goto out;
memset(dptr->data, 0, qset * sizeof(char *));
}
// 如果第s_pos个量子是NULL，申请一块新内存
if (!dptr->data[s_pos]) {
dptr->data[s_pos] = kmalloc(quantum, GFP_KERNEL);
if (!dptr->data[s_pos])
goto out;
}
/* write only up to the end of this quantum */
if (count > quantum - q_pos)
count = quantum - q_pos;
if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) { // 从用户空间拷贝数据到内核空间，失败返回没有拷贝的字节数，成功返回0
retval = -EFAULT;
goto out;
}
*f_pos += count;
retval = count;
/* update the size */
if (dev->size < *f_pos)
dev->size = *f_pos;
out:
up(&dev->sem);
return retval;
}
/*
* The ioctl() implementation
*/
int scull_ioctl(struct inode *inode,
struct file *filp, // 设备文件
unsigned int cmd, // 功能号
unsigned long arg) // 参数: 值，或者用户空间指针
{
int err = 0, tmp;
int retval = 0;
/*
* extract the type and number bitfields, and don't decode
* wrong cmds: return ENOTTY (inappropriate ioctl) before access_ok()
*/
// 对错误的命令，返回ENOTTY TODO
if (_IOC_TYPE(cmd) != SCULL_IOC_MAGIC) return -ENOTTY; // 提取ioctl的类型和功能号，不解码
if (_IOC_NR(cmd) > SCULL_IOC_MAXNR) return -ENOTTY;
/*
* the direction is a bitmask, and VERIFY_WRITE catches R/W
* transfers. `Type' is user-oriented, while
* access_ok is kernel-oriented, so the concept of "read" and
* "write" is reversed
*/
// 如果该ioctl为了读数据，检查当前进程是否可写arg(写到用户空间，用户就读到数据了);如果为了写数据，检查arg是否可读
if (_IOC_DIR(cmd) & _IOC_READ) // _IOC_DIR 获取读写属性域值
// access_ok() 如果当前进程被允许访问用户空间addr处的内存，返回1，否则返回0
err = !access_ok(VERIFY_WRITE, // type: Type of access: %VERIFY_READ or %VERIFY_WRITE.
(void __user *)arg, // addr: User space pointer to start of block to check
_IOC_SIZE(cmd)); // size: Size of block to check. _IOC_SIZE() 读取数据大小域值
else if (_IOC_DIR(cmd) & _IOC_WRITE)
err = !access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));
if (err) return -EFAULT;
switch(cmd) {
// 重置量子集、量子大小 TODO:相关内存不同时整理?
case SCULL_IOCRESET:
scull_quantum = SCULL_QUANTUM;
scull_qset = SCULL_QSET;
break;
// 设置量子大小,arg是指向量子大小值的指针
case SCULL_IOCSQUANTUM: /* Set: arg points to the value */
if (! capable (CAP_SYS_ADMIN)) // 检查是否包含系统管理权限
return -EPERM;
// 取arg所指内容，赋值给scull_quantum
// __get_user() 从用户空间获取一个简单变量，基本不做检查
retval = __get_user(scull_quantum, // x: variable to store result.
(int __user *)arg); // ptr: source address, in user space
break;
// 设置量子大小, arg是值
case SCULL_IOCTQUANTUM: /* Tell: arg is the value */
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
scull_quantum = arg;
break;
// 获取量子大小，arg是指针
case SCULL_IOCGQUANTUM: /* Get: arg is pointer to result */
retval = __put_user(scull_quantum, (int __user *)arg);
break;
// 查询量子大小，返回值 TODO 怎么赋值
case SCULL_IOCQQUANTUM: /* Query: return it (it's positive) */
return scull_quantum;
// 交换量子大小，指针:按arg指向值设置量子大小，当前量子大小保存到arg指向空间
case SCULL_IOCXQUANTUM: /* eXchange: use arg as pointer */
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_quantum;
retval = __get_user(scull_quantum, (int __user *)arg);
if (retval == 0)
retval = __put_user(tmp, (int __user *)arg);
break;
// 交换两字大小，值
case SCULL_IOCHQUANTUM: /* sHift: like Tell + Query */
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_quantum;
scull_quantum = arg;
return tmp;
// 量子集大小，和上面量子功能类似
case SCULL_IOCSQSET: // set
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
retval = __get_user(scull_qset, (int __user *)arg);
break;
case SCULL_IOCTQSET: // tell
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
scull_qset = arg;
break;
case SCULL_IOCGQSET: // get
retval = __put_user(scull_qset, (int __user *)arg);
break;
case SCULL_IOCQQSET: // query
return scull_qset;
case SCULL_IOCXQSET: // eXchange
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_qset;
retval = __get_user(scull_qset, (int __user *)arg);
if (retval == 0)
retval = put_user(tmp, (int __user *)arg);
break;
case SCULL_IOCHQSET: // sHift
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_qset;
scull_qset = arg;
return tmp;
/*
* The following two change the buffer size for scullpipe.
* The scullpipe device uses this same ioctl method, just to
* write less code. Actually, it's the same driver, isn't it?
*/
// tell & query 管道设备缓存大小
case SCULL_P_IOCTSIZE:
scull_p_buffer = arg;
break;
case SCULL_P_IOCQSIZE:
return scull_p_buffer;
default: /* redundant, as cmd was checked against MAXNR */
return -ENOTTY;
}
return retval;
}
/*
* The "extended" operations -- only seek
*/
loff_t scull_llseek(struct file *filp, // 设备文件
loff_t off, // 偏移
int whence) // seek方式
{
struct scull_dev *dev = filp->private_data;
loff_t newpos;
switch(whence) {
case 0: /* SEEK_SET */
newpos = off;
break;
case 1: /* SEEK_CUR */
newpos = filp->f_pos + off;
break;
case 2: /* SEEK_END */
newpos = dev->size + off;
break;
default: /* can't happen */
return -EINVAL;
}
if (newpos < 0) return -EINVAL;
filp->f_pos = newpos;
return newpos;
}
struct file_operations scull_fops = {
.owner = THIS_MODULE,
.llseek = scull_llseek,
.read = scull_read,
.write = scull_write,
.ioctl = scull_ioctl,
.open = scull_open,
.release = scull_release,
};
/*
* Finally, the module stuff
*/
/*
* The cleanup function is used to handle initialization failures as well.
* Thefore, it must be careful to work correctly even if some of the items
* have not been initialized
*/
void scull_cleanup_module(void)
{
int i;
dev_t devno = MKDEV(scull_major, scull_minor); // MKDEV 把主次设备号合成为一个dev_t结构
/* Get rid of our char dev entries */
// 清除字符设备入口
if (scull_devices) {
// 遍历释放每个设备的数据区
for (i = 0; i < scull_nr_devs; i++) {
scull_trim(scull_devices + i); // 释放数据区
cdev_del(&scull_devices[i].cdev); // 移除cdev
}
kfree(scull_devices); // 释放scull_devices本身
}
// 如果使用了/proc来debug，移除创建的/proc文件
#ifdef SCULL_DEBUG /* use proc only if debugging */
scull_remove_proc();
#endif
/* cleanup_module is never called if registering failed */
// 解注册scull_nr_devs个设备号，从devno开始
unregister_chrdev_region(devno, // dev_t from
scull_nr_devs); // unsigned count
/* and call the cleanup functions for friend devices */
scull_p_cleanup();
scull_access_cleanup();
}
/*
* Set up the char_dev structure for this device.
*/
// 建立 char_dev 结构
static void scull_setup_cdev(struct scull_dev *dev, int index)
{
int err, devno = MKDEV(scull_major, scull_minor + index);
cdev_init(&dev->cdev, &scull_fops);
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &scull_fops;
// 添加字符设备dev->cdev，立即生效
err = cdev_add (&dev->cdev, // struct cdev *p: the cdev structure for the device
devno, // dev_t dev: 第一个设备号
1); // unsigned count: 该设备连续次设备号的数目
/* Fail gracefully if need be */
if (err)
printk(KERN_NOTICE "Error %d adding scull%d", err, index);
}
int scull_init_module(void)
{
int result, i;
dev_t dev = 0;
/*
* Get a range of minor numbers to work with, asking for a dynamic
* major unless directed otherwise at load time.
*/
// 申请设备号:获取一系列次设备号, 如果在加载时没有指定主设备号就动态申请一个
if (scull_major) {
dev = MKDEV(scull_major, scull_minor);
// register_chrdev_region 用于已知起始设备的设备号的情况
result = register_chrdev_region(dev, scull_nr_devs, "scull");
} else {
// alloc_chrdev_region 用于设备号未知，向系统动态申请未被占用的设备号情况
result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs,
"scull");
scull_major = MAJOR(dev);
}
if (result < 0) {
printk(KERN_WARNING "scull: can't get major %d\n", scull_major);
return result;
}
/*
* allocate the devices -- we can't have them static, as the number
* can be specified at load time
*/
// 给scull_dev对象申请内存
scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL);
if (!scull_devices) {
result = -ENOMEM;
goto fail; /* Make this more graceful */
}
memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev));
// 初始化 scull_dev
/* Initialize each device. */
for (i = 0; i < scull_nr_devs; i++) {
scull_devices[i].quantum = scull_quantum;
scull_devices[i].qset = scull_qset;
init_MUTEX(&scull_devices[i].sem); // 初始化互斥锁，把信号量sem置为1
scull_setup_cdev(&scull_devices[i], i); // 建立char_dev结构
}
/* At this point call the init function for any friend device */
// TODO
dev = MKDEV(scull_major, scull_minor + scull_nr_devs);
dev += scull_p_init(dev);
dev += scull_access_init(dev);
#ifdef SCULL_DEBUG /* only when debugging */
scull_create_proc();
#endif
return 0; /* succeed */
fail:
scull_cleanup_module();
return result;
}
module_init(scull_init_module);
module_exit(scull_cleanup_module);
access.c
/*
* access.c -- the files with access control on open
*
* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
* Copyright (C) 2001 O'Reilly & Associates
*
* The source code in this file can be freely used, adapted,
* and redistributed in source or binary form, so long as an
* acknowledgment appears in derived source files. The citation
* should list that the code comes from the book "Linux Device
* Drivers" by Alessandro Rubini and Jonathan Corbet, published
* by O'Reilly & Associates. No warranty is attached;
* we cannot take responsibility for errors or fitness for use.
*
* $Id: access.c,v 1.17 2004/09/26 07:29:56 gregkh Exp $
*/
/* FIXME: cloned devices as a use for kobjects? */
#include <linux/kernel.h> /* printk() */
#include <linux/module.h>
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/fcntl.h>
#include <linux/cdev.h>
#include <linux/tty.h>
#include <asm/atomic.h>
#include <linux/list.h>
#include "scull.h" /* local definitions */
static dev_t scull_a_firstdev; /* Where our range begins */
/*
* These devices fall back on the main scull operations. They only
* differ in the implementation of open() and close()
*/
// 这些设备主要的scull操作是相同的，仅读写实现不同?
/************************************************************************
*
* The first device is the single-open one,
* it has an hw structure and an open count
*/
// 第一个设备，只能打开一次。有一个hw结构，和打开计数。 TODO: hw结构是什么?
static struct scull_dev scull_s_device;
// 原子类型，用于计数。初始化原子值为1.
static atomic_t scull_s_available = ATOMIC_INIT(1);
static int scull_s_open(struct inode *inode, struct file *filp)
{
struct scull_dev *dev = &scull_s_device; /* device information */
// 如果scull_s_available计数减1不等于0，计数加1，返回-EBUSY
if (! atomic_dec_and_test (&scull_s_available)) { // 递减原子值；检查是0返回true，否则false
atomic_inc(&scull_s_available);
return -EBUSY; /* already open */
}
// 否则打开设备
/* then, everything else is copied from the bare scull device */
if ( (filp->f_flags & O_ACCMODE) == O_WRONLY)
scull_trim(dev);
filp->private_data = dev;
return 0; /* success */
}
static int scull_s_release(struct inode *inode, struct file *filp)
{
// scull_s_available加1，恢复1了
atomic_inc(&scull_s_available); /* release the device */
return 0;
}
/*
* The other operations for the single-open device come from the bare device
*/
struct file_operations scull_sngl_fops = {
.owner = THIS_MODULE,
.llseek = scull_llseek,
.read = scull_read,
.write = scull_write,
.ioctl = scull_ioctl,
.open = scull_s_open,
.release = scull_s_release,
};
/************************************************************************
*
* Next, the "uid" device. It can be opened multiple times by the
* same user, but access is denied to other users if the device is open
*/
// "uid"设备。可以被同一用户多次打开。拒绝其他用户同时打开。
static struct scull_dev scull_u_device;
static int scull_u_count; /* initialized to 0 by default */
static uid_t scull_u_owner; /* initialized to 0 by default */
static spinlock_t scull_u_lock = SPIN_LOCK_UNLOCKED; // 初始化自旋锁为0
static int scull_u_open(struct inode *inode, struct file *filp)
{
struct scull_dev *dev = &scull_u_device; /* device information */
// 获取自旋锁
spin_lock(&scull_u_lock);
// 如果设备已经被打开，且已打开设备的用户不是当前进程的uid或euid，且不具备CAP_DAC_OVERRIDE能力，则释放自旋锁，返回-EBUSY
// uid表示进程的创建者，euid表示进程对文件和资源的访问权限(具备等同于哪个用户的权限)
// CAP_DAC_OVERRIDE 越过在文件和目录上的访问限制的能力
if (scull_u_count &&
(scull_u_owner != current->uid) && /* allow user */
(scull_u_owner != current->euid) && /* allow whoever did su */
!capable(CAP_DAC_OVERRIDE)) { /* still allow root */
spin_unlock(&scull_u_lock);
return -EBUSY; /* -EPERM would confuse the user */
}
// 如果是第一次打开设备，scull_u_owner设置成当前进程uid
if (scull_u_count == 0)
scull_u_owner = current->uid; /* grab it */
// 递增打开计数。释放自旋锁。
scull_u_count++;
spin_unlock(&scull_u_lock);
/* then, everything else is copied from the bare scull device */
// 打开设备
if ((filp->f_flags & O_ACCMODE) == O_WRONLY)
scull_trim(dev);
filp->private_data = dev;
return 0; /* success */
}
static int scull_u_release(struct inode *inode, struct file *filp)
{
// 获取自旋锁，递减打开计数，释放自旋锁。
spin_lock(&scull_u_lock);
scull_u_count--; /* nothing else */
spin_unlock(&scull_u_lock);
return 0;
}
/*
* The other operations for the device come from the bare device
*/
struct file_operations scull_user_fops = {
.owner = THIS_MODULE,
.llseek = scull_llseek,
.read = scull_read,
.write = scull_write,
.ioctl = scull_ioctl,
.open = scull_u_open,
.release = scull_u_release,
};
/************************************************************************
*
* Next, the device with blocking-open based on uid
*/
// 设备阻塞于open TODO
static struct scull_dev scull_w_device;
static int scull_w_count; /* initialized to 0 by default */
static uid_t scull_w_owner; /* initialized to 0 by default */
static DECLARE_WAIT_QUEUE_HEAD(scull_w_wait);
static spinlock_t scull_w_lock = SPIN_LOCK_UNLOCKED;
// 判断设备是否可用
static inline int scull_w_available(void)
{
// 设备没有被打开，或已打开设备的用户是当前进程的uid或euid，或具备CAP_DAC_OVERRIDE能力，则可用
return scull_w_count == 0 ||
scull_w_owner == current->uid ||
scull_w_owner == current->euid ||
capable(CAP_DAC_OVERRIDE);
}
static int scull_w_open(struct inode *inode, struct file *filp)
{
struct scull_dev *dev = &scull_w_device; /* device information */
// 获取自旋锁
spin_lock(&scull_w_lock);
// 如果设备不可用，则释放自旋锁，等待设备可用后重新申请自旋锁，循环检查设备是否可用
while (! scull_w_available()) {
spin_unlock(&scull_w_lock);
if (filp->f_flags & O_NONBLOCK) return -EAGAIN; // 如果文件以非阻塞模式打开，返回-EAGAIN，让用户层程序再试
if (wait_event_interruptible (scull_w_wait, scull_w_available())) // 等待设备可用。如果等待过程中有异步信号，返回-ERESTARTSYS
return -ERESTARTSYS; /* tell the fs layer to handle it */
spin_lock(&scull_w_lock);
}
// 和上面的"uid"设备一样了
if (scull_w_count == 0)
scull_w_owner = current->uid; /* grab it */
scull_w_count++;
spin_unlock(&scull_w_lock);
/* then, everything else is copied from the bare scull device */
if ((filp->f_flags & O_ACCMODE) == O_WRONLY)
scull_trim(dev);
filp->private_data = dev;
return 0; /* success */
}
static int scull_w_release(struct inode *inode, struct file *filp)
{
int temp;
// 申请自旋锁，递减打开计数，释放自旋锁。
spin_lock(&scull_w_lock);
scull_w_count--;
temp = scull_w_count;
spin_unlock(&scull_w_lock);
// 如果打开计数是0，唤醒scull_w_wait信号
if (temp == 0)
wake_up_interruptible_sync(&scull_w_wait); /* awake other uid's */
return 0;
}
/*
* The other operations for the device come from the bare device
*/
struct file_operations scull_wusr_fops = {
.owner = THIS_MODULE,
.llseek = scull_llseek,
.read = scull_read,
.write = scull_write,
.ioctl = scull_ioctl,
.open = scull_w_open,
.release = scull_w_release,
};
/************************************************************************
*
* Finally the `cloned' private device. This is trickier because it
* involves list management, and dynamic allocation.
*/
// 最后是被克隆的私有设备。
// 这是棘手的，因为涉及列表管理和动态分配。
/* The clone-specific data structure includes a key field */
struct scull_listitem {
struct scull_dev device;
dev_t key;
struct list_head list;
};
// 设备列表，和保护列表的自旋锁
/* The list of devices, and a lock to protect it */
static LIST_HEAD(scull_c_list); // 宏，声明并初始化一个list_head为scull_c_list的静态列表
static spinlock_t scull_c_lock = SPIN_LOCK_UNLOCKED;
/* A placeholder scull_dev which really just holds the cdev stuff. */
// 占位符 scull_dev，实际只有cdev结构 TODO 没看懂。。
static struct scull_dev scull_c_device;
/* Look for a device or create one if missing */
// 查找指定key的设备，如果没有找到就创建一个新的
static struct scull_dev *scull_c_lookfor_device(dev_t key)
{
struct scull_listitem *lptr;
// 遍历scull_listitem，查找指定key的设备
// 结构 struct scull_listitem lptr 中的成员struct list_head list组成了一个链表，链表头是struct list_head scull_c_list
list_for_each_entry(lptr, // pos: the type * to use as a loop cursor
&scull_c_list, // head: 要遍历的链表头
list) { // member: the name of the list_struct within the struct
if (lptr->key == key)
return &(lptr->device); // 返回scull_dev 成员
}
/* not found */
// 如果没有找到指定key的设备，创建一个scull_listitem结构，加在链表中，返回scull_dev成员
lptr = kmalloc(sizeof(struct scull_listitem), GFP_KERNEL);
if (!lptr)
return NULL;
/* initialize the device */
memset(lptr, 0, sizeof(struct scull_listitem));
lptr->key = key;
scull_trim(&(lptr->device)); /* initialize it */
init_MUTEX(&(lptr->device.sem));
/* place it in the list */
list_add(&lptr->list, &scull_c_list);
return &(lptr->device);
}
static int scull_c_open(struct inode *inode, struct file *filp)
{
struct scull_dev *dev;
dev_t key;
// 如果当前设备没有终端，返回-EINVAL(参数无效)
if (!current->signal->tty) {
PDEBUG("Process \"%s\" has no ctl tty\n", current->comm);
return -EINVAL;
}
// 获得当前终端的设备号保存到key中
key = tty_devnum(current->signal->tty);
/* look for a scullc device in the list */
// 从 scull_listitem 中获取指定key的设备(如果没有就创建一个新的返回)-同一终端(key)共用一个设备
spin_lock(&scull_c_lock);
dev = scull_c_lookfor_device(key);
spin_unlock(&scull_c_lock);
if (!dev)
return -ENOMEM;
/* then, everything else is copied from the bare scull device */
if ( (filp->f_flags & O_ACCMODE) == O_WRONLY)
scull_trim(dev);
filp->private_data = dev;
return 0; /* success */
}
static int scull_c_release(struct inode *inode, struct file *filp)
{
/*
* Nothing to do, because the device is persistent.
* A `real' cloned device should be freed on last close
*/
return 0;
}
/*
* The other operations for the device come from the bare device
*/
struct file_operations scull_priv_fops = {
.owner = THIS_MODULE,
.llseek = scull_llseek,
.read = scull_read,
.write = scull_write,
.ioctl = scull_ioctl,
.open = scull_c_open,
.release = scull_c_release,
};
/************************************************************************
*
* And the init and cleanup functions come last
*/
static struct scull_adev_info {
char *name;
struct scull_dev *sculldev;
struct file_operations *fops;
} scull_access_devs[] = {
{ "scullsingle", &scull_s_device, &scull_sngl_fops },
{ "sculluid", &scull_u_device, &scull_user_fops },
{ "scullwuid", &scull_w_device, &scull_wusr_fops },
{ "sullpriv", &scull_c_device, &scull_priv_fops }
};
#define SCULL_N_ADEVS 4
/*
* Set up a single device.
*/
// 给定dev_t和scull_adev_info，建立一个设备
static void scull_access_setup (dev_t devno, struct scull_adev_info *devinfo)
{
struct scull_dev *dev = devinfo->sculldev;
int err;
/* Initialize the device structure */
// 初始化scull_dev结构
dev->quantum = scull_quantum;
dev->qset = scull_qset;
init_MUTEX(&dev->sem);
/* Do the cdev stuff. */
// cdev_init 初始化一个cdev结构
cdev_init(&dev->cdev, // struct cdev *cdev: 要初始化的结构
devinfo->fops); // const struct file_operations *fops: 该设备的 file_operations
// kobject_set_name 给kobject设置名字
kobject_set_name(&dev->cdev.kobj, // struct kobject *kobj: 要设置名字的结构
devinfo->name); // const char *fmt: 用来创建名字的格式化字符串
dev->cdev.owner = THIS_MODULE;
// cdev_add() 给系统中添加一个字符设备 &dev->cdev。立即生效。出错时返回一个负的错误码。
err = cdev_add (&dev->cdev, // struct cdev *p: 设备的cdev结构
devno, // dev_t dev: 设备的第一个设备号
1); // unsigned count: 设备对应的连续次设备号
/* Fail gracefully if need be */
// 如果添加设备出错，dev->cdev.kobject引用计数减1
if (err) {
printk(KERN_NOTICE "Error %d adding %s\n", err, devinfo->name);
// kobject_put 递减设备的引用计数。如果引用计数为0，调用 kobject_cleanup()
kobject_put(&dev->cdev.kobj); // struct kobject *kobj
} else
printk(KERN_NOTICE "%s registered at %x\n", devinfo->name, devno);
}
int scull_access_init(dev_t firstdev)
{
int result, i;
/* Get our number space */
// 注册 SCULL_N_ADEVS 个设备号
// register_chrdev_region() 注册一系列设备号。成功返回0，失败返回一个负的错误码。
result = register_chrdev_region (firstdev, // dev_t from: 要注册的第一个设备号，必须包含主设备号。
SCULL_N_ADEVS, // unsigned count: 需要的连续设备号个数
"sculla"); // const char *name: 设备或驱动名称
if (result < 0) {
printk(KERN_WARNING "sculla: device number registration failed\n");
return 0;
}
scull_a_firstdev = firstdev;
/* Set up each device. */
// 循环给系统中添加 SCULL_N_ADEVS 个字符设备
for (i = 0; i < SCULL_N_ADEVS; i++)
scull_access_setup (firstdev + i, scull_access_devs + i);
return SCULL_N_ADEVS;
}
/*
* This is called by cleanup_module or on failure.
* It is required to never fail, even if nothing was initialized first
*/
void scull_access_cleanup(void)
{
struct scull_listitem *lptr, *next;
int i;
/* Clean up the static devs */
// 遍历清除scull_acess_dev中每个静态设备: 移除cdev，释放sculldev数据区
for (i = 0; i < SCULL_N_ADEVS; i++) {
struct scull_dev *dev = scull_access_devs[i].sculldev;
// 从系统中删除dev->cdev
// cdev_del() 从系统中移除一个 cdev ，可能要自己释放结构
cdev_del(&dev->cdev); // struct cdev *p: 要移除的cdev结构
scull_trim(scull_access_devs[i].sculldev);
}
/* And all the cloned devices */
// 遍历清除 scull_listitem中每个cloned设备: 删除list_head，释放sculldev数据区，释放scull_listitem结构内存
// list_for_each_entry_safe 要求调用者另外提供一个与pos(lptr)同类型的指针next，在for循环中暂存pos的下一个节点的地址，避免因pos节点被释放而造成的断链
list_for_each_entry_safe(lptr, next, &scull_c_list, list) {
// list_del 删除链表的entry
list_del(&lptr->list); // struct list_head *entry: 要从链表中删除的元素
scull_trim(&(lptr->device));
kfree(lptr);
}
/* Free up our number space */
// unregister_chrdev_region 解注册从scull_a_firstdev开始的连续SCULL_N_ADEVS个设备
unregister_chrdev_region(scull_a_firstdev, // dev_t from
SCULL_N_ADEVS); // unsigned count
return;
}
pipe.c
/*
* pipe.c -- fifo driver for scull
*
* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
* Copyright (C) 2001 O'Reilly & Associates
*
* The source code in this file can be freely used, adapted,
* and redistributed in source or binary form, so long as an
* acknowledgment appears in derived source files. The citation
* should list that the code comes from the book "Linux Device
* Drivers" by Alessandro Rubini and Jonathan Corbet, published
* by O'Reilly & Associates. No warranty is attached;
* we cannot take responsibility for errors or fitness for use.
*
*/
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h> /* printk(), min() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything */
#include <linux/proc_fs.h>
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/fcntl.h>
#include <linux/poll.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#include "scull.h" /* local definitions */
struct scull_pipe {
wait_queue_head_t inq, outq; /* read and write queues */ // wait_queue_head_t 等待队列头
char *buffer, *end; /* begin of buf, end of buf */
int buffersize; /* used in pointer arithmetic */
char *rp, *wp; /* where to read, where to write */
int nreaders, nwriters; /* number of openings for r/w */
struct fasync_struct *async_queue; /* asynchronous readers */ // 异步操作的文件指针结构 TODO
struct semaphore sem; /* mutual exclusion semaphore */
struct cdev cdev; /* Char device structure */
};
/* parameters */
static int scull_p_nr_devs = SCULL_P_NR_DEVS; /* number of pipe devices */
int scull_p_buffer = SCULL_P_BUFFER; /* buffer size */
dev_t scull_p_devno; /* Our first device number */
// 模块加载时，指定管道设备数量、缓存大小
module_param(scull_p_nr_devs, int, 0); /* FIXME check perms */
module_param(scull_p_buffer, int, 0);
static struct scull_pipe *scull_p_devices;
static int scull_p_fasync(int fd, struct file *filp, int mode);
static int spacefree(struct scull_pipe *dev);
/*
* Open and close
*/
static int scull_p_open(struct inode *inode, struct file *filp)
{
struct scull_pipe *dev;
// 获取和inode->i_cdev对应的管道设备(scull_pipe结构)指针
// container_of: cdev嵌套在struct scull_pipe中，由指向cdev成员的指针，获得指向struct scull_pipe的指针
dev = container_of(inode->i_cdev, // ptr: 指向成员的指针
struct scull_pipe, // type: 容器结构的类型
cdev); // member: 成员名称
filp->private_data = dev;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
// 如果dev->buffer为NULL，申请缓存
if (!dev->buffer) {
/* allocate the buffer */
dev->buffer = kmalloc(scull_p_buffer, GFP_KERNEL);
if (!dev->buffer) {
up(&dev->sem);
return -ENOMEM;
}
}
// 给dev成员设初值
dev->buffersize = scull_p_buffer;
dev->end = dev->buffer + dev->buffersize;
dev->rp = dev->wp = dev->buffer; /* rd and wr from the beginning */
/* use f_mode,not f_flags: it's cleaner (fs/open.c tells why) */
// 递增设备打开计数，区分读写模式。
if (filp->f_mode & FMODE_READ)
dev->nreaders++;
if (filp->f_mode & FMODE_WRITE)
dev->nwriters++;
up(&dev->sem);
// 通知内核设备不支持移位llseek
return nonseekable_open(inode, filp);
}
static int scull_p_release(struct inode *inode, struct file *filp)
{
struct scull_pipe *dev = filp->private_data;
/* remove this filp from the asynchronously notified filp's */
scull_p_fasync(-1, filp, 0); // TODO
down(&dev->sem);
// 设备打开计数减1。打开计数为0时清空设备缓存。
if (filp->f_mode & FMODE_READ)
dev->nreaders--;
if (filp->f_mode & FMODE_WRITE)
dev->nwriters--;
if (dev->nreaders + dev->nwriters == 0) {
kfree(dev->buffer);
dev->buffer = NULL; /* the other fields are not checked on open */
}
up(&dev->sem);
return 0;
}
/*
* Data management: read and write
*/
static ssize_t scull_p_read (struct file *filp, char __user *buf, size_t count,
loff_t *f_pos)
{
struct scull_pipe *dev = filp->private_data;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
// 如果缓冲区空(读写指针重合)，循环等待缓冲区中有数据可读。
while (dev->rp == dev->wp) { /* nothing to read */
up(&dev->sem); /* release the lock */
if (filp->f_flags & O_NONBLOCK) // 非阻塞打开
return -EAGAIN;
PDEBUG("\"%s\" reading: going to sleep\n", current->comm);
if (wait_event_interruptible(dev->inq, (dev->rp != dev->wp))) // 异步信号
return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
/* otherwise loop, but first reacquire the lock */
if (down_interruptible(&dev->sem)) // 可被中断地获取信号量
return -ERESTARTSYS;
}
// 数据读取到用户空间。最多读取到dev->end(线程非循环缓冲)
/* ok, data is there, return something */
if (dev->wp > dev->rp)
count = min(count, (size_t)(dev->wp - dev->rp));
else /* the write pointer has wrapped, return data up to dev->end */
count = min(count, (size_t)(dev->end - dev->rp));
if (copy_to_user(buf, dev->rp, count)) {
up (&dev->sem);
return -EFAULT;
}
// 读位置修改
dev->rp += count;
if (dev->rp == dev->end) // 如果读到缓存结尾了，读位置移至缓存开头
dev->rp = dev->buffer; /* wrapped */
up (&dev->sem);
/* finally, awake any writers and return */
wake_up_interruptible(&dev->outq);
PDEBUG("\"%s\" did read %li bytes\n",current->comm, (long)count);
return count;
}
/* Wait for space for writing; caller must hold device semaphore. On
* error the semaphore will be released before returning. */
static int scull_getwritespace(struct scull_pipe *dev, struct file *filp)
{
// 如果缓存已满
// apacefree返回缓存中可写空间个数
while (spacefree(dev) == 0) { /* full */
// 初始化等待队列
DEFINE_WAIT(wait); // DEFINE_WAIT 创建和初始化一个等待队列。wait是队列入口项的名字。
up(&dev->sem);
if (filp->f_flags & O_NONBLOCK) // 如果文件在非阻塞模式，立即返回
return -EAGAIN;
PDEBUG("\"%s\" writing: going to sleep\n",current->comm);
// 添加写等待队列入口，设置进程状态为可中断休眠
// prepare_to_wait()添加等待队列入口到队列，并设置进程状态
prepare_to_wait(&dev->outq, // wait_queue_head_t *queue: 等待队列头
&wait, // wait_queue_t *wait: 进程入口
TASK_INTERRUPTIBLE); // int state: 进程新状态 TASK_INTERRUPTIBLE 可中断休眠
// 在检查确认仍然需要休眠之后，调用schedule
if (spacefree(dev) == 0)
schedule(); // TODO
// 条件满足退出后，确保状态为running，同时将进程从等待队列中删除。
finish_wait(&dev->outq, // wait_queue_head_t *queue
&wait); // wait_queue_t *wait
// 如果当前进程有信号处理，返回-ERESTARTSYS
if (signal_pending(current)) // signal_pending 检查当前进程是否有信号处理，返回不为0表示有信号需要处理
return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
// 获取信号量，除非发生中断
// down_iterruptible尝试获取信号量。如果没有更多任务被允许获取信号量，该任务投入睡眠等待；如果睡眠被信号打断，返回-EINTR；如果成功获取信号量，返回0
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
}
return 0;
}
/* How much space is free? */
// 获取dev空闲空间个数
static int spacefree(struct scull_pipe *dev)
{
if (dev->rp == dev->wp)
return dev->buffersize - 1;
return ((dev->rp + dev->buffersize - dev->wp) % dev->buffersize) - 1; // todo
}
static ssize_t scull_p_write(struct file *filp, const char __user *buf, size_t count,
loff_t *f_pos)
{
struct scull_pipe *dev = filp->private_data;
int result;
// 获取信号量
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
/* Make sure there's space to write */
// 如果没有空间可写，返回错误码
result = scull_getwritespace(dev, filp);
if (result)
return result; /* scull_getwritespace called up(&dev->sem) */
/* ok, space is there, accept something */
count = min(count, (size_t)spacefree(dev)); // apacefree 获取空闲空间个数
if (dev->wp >= dev->rp)
count = min(count, (size_t)(dev->end - dev->wp)); /* to end-of-buf */
else /* the write pointer has wrapped, fill up to rp-1 */
count = min(count, (size_t)(dev->rp - dev->wp - 1));
PDEBUG("Going to accept %li bytes to %p from %p\n", (long)count, dev->wp, buf);
if (copy_from_user(dev->wp, buf, count)) {
up (&dev->sem);
return -EFAULT;
}
dev->wp += count;
if (dev->wp == dev->end)
dev->wp = dev->buffer; /* wrapped */
up(&dev->sem);
/* finally, awake any reader */
wake_up_interruptible(&dev->inq); /* blocked in read() and select() */
/* and signal asynchronous readers, explained late in chapter 5 */
if (dev->async_queue)
kill_fasync(&dev->async_queue, SIGIO, POLL_IN);
PDEBUG("\"%s\" did write %li bytes\n",current->comm, (long)count);
return count;
}
static unsigned int scull_p_poll(struct file *filp, poll_table *wait)
{
struct scull_pipe *dev = filp->private_data;
unsigned int mask = 0;
/*
* The buffer is circular; it is considered full
* if "wp" is right behind "rp" and empty if the
* two are equal.
*/
// 环形缓冲: wp在rp右侧表示缓冲区满；wp==rp表示空。
// down() 检查dev->sem是否大于0.如果大于0，将值减1;如果等于0,进程投入睡眠.
down(&dev->sem);
// 把当前进程添加到wait参数指定的等待列表中
poll_wait(filp, // struct file *filp
&dev->inq, // wait_queue_head_t * wait_address
wait); // poll_table *p
poll_wait(filp, &dev->outq, wait);
// 如果缓存不空，可读
if (dev->rp != dev->wp)
mask |= POLLIN | POLLRDNORM; /* readable */
// 如果缓存不满，可写
if (spacefree(dev))
mask |= POLLOUT | POLLWRNORM; /* writable */
// 释放信号量
up(&dev->sem);
return mask;
}
static int scull_p_fasync(int fd, struct file *filp, int mode)
{
struct scull_pipe *dev = filp->private_data;
// 设置 fasync 队列。
// fasync_helper()从相关的进程列表中添加或去除入口项。出错返回负数，没有改变返回0，添加删除entry返回正数。
return fasync_helper(fd, filp, mode, &dev->async_queue);
}
/* FIXME this should use seq_file */
#ifdef SCULL_DEBUG
static void scullp_proc_offset(char *buf, char **start, off_t *offset, int *len)
{
if (*offset == 0)
return;
if (*offset >= *len) { /* Not there yet */
*offset -= *len;
*len = 0;
}
else { /* We're into the interesting stuff now */
*start = buf + *offset;
*offset = 0;
}
}
static int scull_read_p_mem(char *buf, char **start, off_t offset, int count,
int *eof, void *data)
{
int i, len;
struct scull_pipe *p;
#define LIMIT (PAGE_SIZE-200) /* don't print any more after this size */
*start = buf;
// len 记录读取字节数
len = sprintf(buf, "Default buffersize is %i\n", scull_p_buffer);
// 遍历每一个管道设备，总输出长度不大于LIMIT
for(i = 0; i<scull_p_nr_devs && len <= LIMIT; i++) {
p = &scull_p_devices[i];
if (down_interruptible(&p->sem)) // 可中断的申请信号量
return -ERESTARTSYS;
len += sprintf(buf+len, "\nDevice %i: %p\n", i, p);
/* len += sprintf(buf+len, " Queues: %p %p\n", p->inq, p->outq);*/
len += sprintf(buf+len, " Buffer: %p to %p (%i bytes)\n", p->buffer, p->end, p->buffersize);
len += sprintf(buf+len, " rp %p wp %p\n", p->rp, p->wp);
len += sprintf(buf+len, " readers %i writers %i\n", p->nreaders, p->nwriters);
up(&p->sem);
// TODO: 移动偏移量?
scullp_proc_offset(buf, start, &offset, &len);
}
*eof = (len <= LIMIT);
return len;
}
#endif
/*
* The file operations for the pipe device
* (some are overlayed with bare scull)
*/
struct file_operations scull_pipe_fops = {
.owner = THIS_MODULE,
.llseek = no_llseek,
.read = scull_p_read,
.write = scull_p_write,
.poll = scull_p_poll,
.ioctl = scull_ioctl,
.open = scull_p_open,
.release = scull_p_release,
.fasync = scull_p_fasync,
};
/*
* Set up a cdev entry.
*/
static void scull_p_setup_cdev(struct scull_pipe *dev, int index)
{
int err, devno = scull_p_devno + index;
cdev_init(&dev->cdev, &scull_pipe_fops);
dev->cdev.owner = THIS_MODULE;
err = cdev_add (&dev->cdev, devno, 1);
/* Fail gracefully if need be */
if (err)
printk(KERN_NOTICE "Error %d adding scullpipe%d", err, index);
}
/*
* Initialize the pipe devs; return how many we did.
*/
// 初始化管道设备; 返回管道设备个数。
int scull_p_init(dev_t firstdev)
{
int i, result;
// 注册一系列设备号。成功返回0，失败返回一个负的错误码。
result = register_chrdev_region(firstdev, // dev_t from: 要注册的第一个设备号，必须包含主设备号
scull_p_nr_devs, // unsigned count: 需要的连续设备号个数
"scullp"); // const char *name: 设备或驱动名称
if (result < 0) {
printk(KERN_NOTICE "Unable to get scullp region, error %d\n", result);
return 0;
}
scull_p_devno = firstdev; // 第一个设备号
// 申请scull_p_nr_devs个scull_pipe设备的存储空间
scull_p_devices = kmalloc(scull_p_nr_devs * sizeof(struct scull_pipe), GFP_KERNEL);
if (scull_p_devices == NULL) {
unregister_chrdev_region(firstdev, scull_p_nr_devs);
return 0;
}
memset(scull_p_devices, 0, scull_p_nr_devs * sizeof(struct scull_pipe));
for (i = 0; i < scull_p_nr_devs; i++) {
// 初始化读写等待队列头
init_waitqueue_head(&(scull_p_devices[i].inq));
init_waitqueue_head(&(scull_p_devices[i].outq));
// 初始化互斥信号量，sem置1
init_MUTEX(&scull_p_devices[i].sem);
// 建立字符设备入口
scull_p_setup_cdev(scull_p_devices + i, i);
}
#ifdef SCULL_DEBUG
create_proc_read_entry("scullpipe", 0, NULL, scull_read_p_mem, NULL);
#endif
return scull_p_nr_devs;
}
/*
* This is called by cleanup_module or on failure.
* It is required to never fail, even if nothing was initialized first
*/
void scull_p_cleanup(void)
{
int i;
#ifdef SCULL_DEBUG
remove_proc_entry("scullpipe", NULL);
#endif
if (!scull_p_devices)
return; /* nothing else to release */
for (i = 0; i < scull_p_nr_devs; i++) {
cdev_del(&scull_p_devices[i].cdev);
kfree(scull_p_devices[i].buffer);
}
kfree(scull_p_devices);
unregister_chrdev_region(scull_p_devno, scull_p_nr_devs);
scull_p_devices = NULL; /* pedantic */
} http://linux.chinaunix.net/bbs/thread-967565-1-1.html
http://www.ibm.com/developerworks/cn/linux/l-proc.html
源码：/Files/momoxiao/scull.zip