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Proc文件系统剖析

2009-12-20 13:42| 发布者: admin| 查看: 60| 评论: 0|原作者: 柳梦璃


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文件:
proc.pdf
大小:
73KB
下载:
下载
Proc file system
dreamice.jiang@gmail.com
1、重要的数据结构:
struct proc_dir_entry {
unsigned int low_ino;
unsigned short namelen;
const char *name;
mode_t mode;
nlink_t nlink;
uid_t uid;
gid_t gid;
loff_t size;
const struct inode_operations *proc_iops;
/*
* NULL ->proc_fops means "PDE is going away RSN" or
* "PDE is just created". In either case, e.g. ->read_proc won't be
* called because it's too late or too early, respectively.
*
* If you're allocating ->proc_fops dynamically, save a pointer
* somewhere.
*/
const struct file_operations *proc_fops;
get_info_t *get_info;
struct module *owner;
struct proc_dir_entry *next, *parent, *subdir;
void *data;
read_proc_t *read_proc;
write_proc_t *write_proc;
atomic_t count; /* use count */
int pde_users; /* number of callers into module in progress */
spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
struct completion *pde_unload_completion;
shadow_proc_t *shadow_proc;
};
2、创建函数:
struct proc_dir_entry *create_proc_entry(const char *name, mode_t mode,
struct proc_dir_entry *parent);
name: 要创建的文件名称;
mode: 该文件的保护掩码;
parent: 确定文件所在目录,如果置NULL,则位置为/proc下。
3、读proc:
int read_proc(char *page, char **start, off_t off,
int count, int *eof, void *data);
page:指示用来写入数据的缓冲区;
off和count:与read函数对应的参数相同;
start和eof:用于读取大于1个page数据时实现。
4、写proc:
int write_proc(struct file *file, const char __user *buffer,
unsigned long count, void *data);
filp 参数实际上是一个打开文件结构(可以忽略这个参数)。Buffer 参数是用户空间要写入的数据。缓冲区地址实际上是一个用户空间的缓冲区,不能直接读取它。len 参数定义了在 buffer 中有多少数据要被写入。data 参数是一个指向私有数据的指针。
5、实现一个proc文件
(1)调用create_proc_entry创建一个struct proc_dir_entry,作为一个全局量。
(2)对创建的struct proc_dir_entry进行赋值:read_proc,mode,owner,size,write_proc等等。
示例:
proc_hello.c
#include /* Specifically, a module */
#include /* We're doing kernel work */
#include /* Necessary because we use the proc fs */
#define procfs_name "helloworld"
struct proc_dir_entry *Our_Proc_File;
int
procfile_read(char *buffer,
char **buffer_location,
off_t offset, int buffer_length, int *eof, void *data)
{
int ret;
printk(KERN_INFO "procfile_read (/proc/%s) called\n", procfs_name);
/*
* We give all of our information in one go, so if the
* user asks us if we have more information the
* answer should always be no.
*
* This is important because the standard read
* function from the library would continue to issue
* the read system call until the kernel replies
* that it has no more information, or until its
* buffer is filled.
*/
if (offset > 0) {
printk(KERN_INFO "offset > 0\n");
/* we have finished to read, return 0 */
ret = 0;
} else {
/* fill the buffer, return the buffer size */
printk(KERN_INFO "offset read_proc = procfile_read;
Our_Proc_File->owner = THIS_MODULE;
Our_Proc_File->mode = S_IFREG | S_IRUGO;
Our_Proc_File->uid = 0;
Our_Proc_File->gid = 0;
Our_Proc_File->size = 37;
printk(KERN_INFO "/proc/%s created\n", procfs_name);
return 0; /* everything is ok */
}
void cleanup_module()
{
remove_proc_entry(procfs_name, &proc_root);
printk(KERN_INFO "/proc/%s removed\n", procfs_name);
}
Makefile:
obj-m := proc_hello.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KDIR) M=$(PWD) modules
clean:
$(RM) *.o *.mod.c *.ko *.symvers
本示例只实现了一个简单的读proc操作。
编译后,执行:
# insmod proc_hello.ko
# dmesg
/proc/helloworld created
# cat /proc/ helloworld
HelloWorld!
# dmesg
procfile_read (/proc/helloworld) called
offset 0
procfile_read (/proc/helloworld) called
offset > 0
# rmmod proc_hello
/proc/helloworld
为什么在调用cat /proc/ helloworld后,会看到procfile_read被执行了三次,且只有第一次读到了数据?
因为通常cat,dd等,都是通过标准库函数来实现的,标准库函数往往会多次调用系统调用来读写数据,所以我们看到调用了3次。具体cat以及dd等调用一次,读取或写数据大小,这个需要具体查证一下。
我写了一个test程序,来验证这个多次读操作不是在系统调用里面实现的:
test.c
#include
#include
#include
#include
#include
#include
#define PROC_FILE "/proc/helloworld"
int main()
{
char buf[50];
int fd = open(PROC_FILE, O_RDONLY);
if (fd == -1) {
printf("open err\n");
return -1;
}
if (read(fd, buf, sizeof("HelloWorld")) > 0) {
printf("read: %s\n", buf);
}
close(fd);
}
编译:
# gcc test.c –o test
加载模块后,执行
# ./test
然后,执行:
# dmesg
procfile_read (/proc/helloworld) called
offset





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