procfs作为linux的一种伪文件系统，主要用于内核与用户层交换信息；
在linux中的/proc就是作为procfs使用，该目录下面有cpu，mtd，gio等固有的节点等，如果用cat命令去查看这些文件，就能够看到这些文件所代表设备的相关信息；
同时procfs也可以提供给用户层写的操作，只要在相关文件驱动中支持就可以；
下面是一个简单的添加一个proc节点的例子，参考 http://www.tldp.org/LDP/lkmpg/2.6/html/x710.html
【环境】
内核用的是TI的2.6.37_IPNC_DM365_4.0.0
【Makefile】
#TARGET = cmemk.ko
obj-m += myproc.o
LINUXKERNEL_INSTALL_DIR = /home/mao/workroom/build_for_nand/psp/trunk/ipnc_psp_03_21_00_04/ti-davinci
MAKE_ENV = ARCH=arm CROSS_COMPILE=arm_v5t_le-
debug: EXTRA_CFLAGS += -D__DEBUG
.PHONY: clean debug release install default
default: debug
docs:
release:
make -C $(LINUXKERNEL_INSTALL_DIR) M=`pwd` $(MAKE_ENV) \
EXTRA_CFLAGS="$(EXTRA_CFLAGS)"
debug:
make -C $(LINUXKERNEL_INSTALL_DIR) M=`pwd` $(MAKE_ENV) \
EXTRA_CFLAGS="$(EXTRA_CFLAGS)" modules
install:
install -d $(EXEC_DIR)
clean:
-rm -rf *.o *mod* *.ko .cmem* .tmp*
【源码】
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/unistd.h>
#include <linux/spinlock.h>
#include <linux/kmod.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#define procfs_name "helloworld"
/**
* This structure hold information about the /proc file
*
*/
struct proc_dir_entry *Our_Proc_File;
/* Put data into the proc fs file.
*
* Arguments
* =========
* 1. The buffer where the data is to be inserted, if
* you decide to use it.
* 2. A pointer to a pointer to characters. This is
* useful if you don't want to use the buffer
* allocated by the kernel.
* 3. The current position in the file
* 4. The size of the buffer in the first argument.
* 5. Write a "1" here to indicate EOF.
* 6. A pointer to data (useful in case one common
* read for multiple /proc/... entries)
*
* Usage and Return Value
* ======================
* A return value of zero means you have no further
* information at this time (end of file). A negative
* return value is an error condition.
*
* For More Information
* ====================
* The way I discovered what to do with this function
* wasn't by reading documentation, but by reading the
* code which used it. I just looked to see what uses
* the get_info field of proc_dir_entry struct (I used a
* combination of find and grep, if you're interested),
* and I saw that it is used in <kernel source
* directory>/fs/proc/array.c.
*
* If something is unknown about the kernel, this is
* usually the way to go. In Linux we have the great
* advantage of having the kernel source code for
* free - use it.
*/
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) {
/* we have finished to read, return 0 */
ret = 0;
} else {
/* fill the buffer, return the buffer size */
ret = sprintf(buffer, "HelloWorld!\n");
}
return ret;
}
int init_module()
{
Our_Proc_File = create_proc_entry(procfs_name, 0644, NULL);
if (Our_Proc_File == NULL) {
remove_proc_entry(procfs_name, NULL);
printk(KERN_ALERT "Error: Could not initialize /proc/%s\n",
procfs_name);
return -ENOMEM;
}
Our_Proc_File->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, NULL);
printk(KERN_INFO "/proc/%s removed\n", procfs_name);
}