LDD-LinuxDeviceDrivers/study/proc/proc_create_data/jif.c

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/uaccess.h>
#include <linux/slab.h>

// global var
static char *str = NULL;

// linux/seq_file.h
// void * (*start) (struct seq_file *m, loff_t *pos);
// void (*stop) (struct seq_file *m, void *v);
// void * (*next) (struct seq_file *m, void *v, loff_t *pos);
// int (*show) (struct seq_file *m, void *v);

/**
* author:  aran
* fuction: seq_operations -> start
*/
static void *my_seq_start(struct seq_file *m, loff_t *pos)
{
    if (0 == *pos)
    {
        ++*pos;
        return (void *)1; // return anything but NULL, just for test
    }
    return NULL;
}

/**
* author:  aran
* fuction: seq_operations -> next
*/
static void *my_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
    // only once, so no next
    return NULL;
}

/**
* author:  aran
* fuction: seq_operations -> stop
*/
static void my_seq_stop(struct seq_file *m, void *v)
{
    // clean sth.
    // nothing to do
}

/**
* author:  aran
* fuction: seq_operations -> show
*/
static int my_seq_show(struct seq_file *m, void *v)
{
    seq_printf(m, "current kernel time is %llu\n", (unsigned long long) get_jiffies_64());
    seq_printf(m, "str is %s\n", str);

    return 0; //!! must be 0, or will show nothing T.T
}

// global var
static struct seq_operations my_seq_fops =
{
    .start  = my_seq_start,
    .next   = my_seq_next,
    .stop   = my_seq_stop,
    .show   = my_seq_show,
};

// file_operations
// int (*open) (struct inode *, struct file *)
// ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *)

/**
* author:  aran
* fuction: file_operations -> open
*/
static int proc_seq_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &my_seq_fops);
}

/**
* author:  aran
* fuction: file_operations -> write
*/
static ssize_t proc_seq_write(struct file *file, const char __user *buffer, size_t count, loff_t *f_pos)
{
    //分配临时缓冲区
    char *tmp = kzalloc((count+1), GFP_KERNEL);
    if (!tmp)
        return -ENOMEM;

    //将用户态write的字符串拷贝到内核空间
    //copy_to|from_user(to,from,cnt)
    if (copy_from_user(tmp, buffer, count)) {
        kfree(tmp);
        return -EFAULT;
    }

    //将str的旧空间释放，然后将tmp赋值给str
    kfree(str);
    str = tmp;

    return count;
}

// global var
static struct file_operations proc_seq_fops =
{
    .owner      = THIS_MODULE,
    .open       = proc_seq_open,
    .read       = seq_read,
    .write      = proc_seq_write,
    .llseek     = seq_lseek,
    .release    = seq_release,
};

static int __init my_init(void)
{
    struct proc_dir_entry *file;

    // create "/proc/proc_seq" file
    file = proc_create_data(
        "jif",      // name
        0666,       // mode
        NULL,       // parent dir_entry
        &proc_seq_fops, // file_operations
        NULL        // data
        );
    if (NULL == file)
    {
        printk("Count not create /proc/jif file!\n");
        return -ENOMEM;
    }

    return 0;
}

static void __exit my_exit(void)
{
    remove_proc_entry("jif", NULL);
    kfree(str);
}

module_init(my_init);
module_exit(my_exit);

MODULE_AUTHOR("aran");
MODULE_LICENSE("GPL");