procfs_demo.c

李亚锋出的书《ARM嵌入式LINUX设备驱动实例开发》一书的码源！

// This is a simple proc filesytem demo.
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/jiffies.h>
#include <asm/uaccess.h>


#define MODULE_VERS "1.0"
#define MODULE_NAME "procfs_demo"

#define FOOBAR_LEN 8

struct fb_data_t {
	char name[FOOBAR_LEN + 1];
	char value[FOOBAR_LEN + 1];
};


static struct proc_dir_entry *demo_dir, *foo_file,
	*bar_file, *jiffies_file, *symlink;


struct fb_data_t foo_data, bar_data;


static int proc_read_jiffies(char *page, char **start,
			     off_t off, int count,
			     int *eof, void *data)
{
	int len;

	len = sprintf(page, "jiffies = %ld\n",
                      jiffies);

	return len;
}

static int proc_read_foobar(char *page, char **start,
			    off_t off, int count, 
			    int *eof, void *data)
{
	int len;
	struct fb_data_t *fb_data = (struct fb_data_t *)data;

	/* DON'T DO THAT - buffer overruns are bad */
	len = sprintf(page, "%s = %s\n", 
		      fb_data->name, fb_data->value);

	return len;
}

static int proc_write_foobar(struct file *file,
			     const char *buffer,
			     unsigned long count, 
			     void *data)
{
	int len;
	struct fb_data_t *fb_data = (struct fb_data_t *)data;

	if(count > FOOBAR_LEN)
		len = FOOBAR_LEN;
	else
		len = count;

	if(copy_from_user(fb_data->value, buffer, len))
		return -EFAULT;

	fb_data->value[len] = '\0';

	return len;
}

static int __init init_procfs_demo(void)
{
	int rv = 0;

	/* create directory */
	demo_dir = proc_mkdir(MODULE_NAME, NULL);
	if(demo_dir == NULL) {
		rv = -ENOMEM;
		goto out;
	}
	
	demo_dir->owner = THIS_MODULE;
	
	/* create jiffies using convenience function */
	jiffies_file = create_proc_read_entry("jiffies", 
					      0444, demo_dir, 
					      proc_read_jiffies,
					      NULL);
	if(jiffies_file == NULL) {
		rv  = -ENOMEM;
		goto no_jiffies;
	}

	jiffies_file->owner = THIS_MODULE;

	/* create foo and bar files using same callback
	 * functions 
	 */
	foo_file = create_proc_entry("foo", 0644, demo_dir);
	if(foo_file == NULL) {
		rv = -ENOMEM;
		goto no_foo;
	}

	strcpy(foo_data.name, "foo");
	strcpy(foo_data.value, "foo");
	foo_file->data = &foo_data;
	foo_file->read_proc = proc_read_foobar;
	foo_file->write_proc = proc_write_foobar;
	foo_file->owner = THIS_MODULE;
		
	bar_file = create_proc_entry("bar", 0644, demo_dir);
	if(bar_file == NULL) {
		rv = -ENOMEM;
		goto no_bar;
	}

	strcpy(bar_data.name, "bar");
	strcpy(bar_data.value, "bar");
	bar_file->data = &bar_data;
	bar_file->read_proc = proc_read_foobar;
	bar_file->write_proc = proc_write_foobar;
	bar_file->owner = THIS_MODULE;
		
	/* create symlink */
	symlink = proc_symlink("jiffies_too", demo_dir, 
			       "jiffies");
	if(symlink == NULL) {
		rv = -ENOMEM;
		goto no_symlink;
	}

	symlink->owner = THIS_MODULE;

	/* everything OK */
	printk(KERN_INFO "%s %s initialised\n",
	       MODULE_NAME, MODULE_VERS);
	return 0;

no_symlink:
	remove_proc_entry("tty", demo_dir);
no_bar:
	remove_proc_entry("foo", demo_dir);
no_foo:
	remove_proc_entry("jiffies", demo_dir);
no_jiffies:			      
	remove_proc_entry(MODULE_NAME, NULL);
out:
	return rv;
}

static void __exit cleanup_procfs_demo(void)
{
	remove_proc_entry("jiffies_too", demo_dir);
	remove_proc_entry("tty", demo_dir);
	remove_proc_entry("bar", demo_dir);
	remove_proc_entry("foo", demo_dir);
	remove_proc_entry("jiffies", demo_dir);
	remove_proc_entry(MODULE_NAME, NULL);

	printk(KERN_INFO "%s %s removed\n",
	       MODULE_NAME, MODULE_VERS);
}


module_init(init_procfs_demo);
module_exit(cleanup_procfs_demo);

MODULE_DESCRIPTION("procfs examples");