kmem_cache简单用法

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <asm/uaccess.h>

#define DEVICE_NAME "chardev"

static ssize_t chardev_read(struct file *filp, char __user *buff, size_t count, loff_t *f_pos);

static struct file_operations chardev_fops = {
        .read = chardev_read,
};

static struct kmem_cache *cachep = NULL;
static struct cdev *cdevp = NULL;
static dev_t devno = -1;

static ssize_t chardev_read(struct file *filp, char __user *buff, size_t count, loff_t *f_pos)
{
        char *p = NULL;
        unsigned long n;

        p = kmem_cache_alloc(cachep, GFP_KERNEL);
        if (p)
                memset(p, '1', 40);
        else
                goto err;

        n = copy_to_user(buff, p, 40);

        kmem_cache_free(cachep, p);

        return 40;
err:
        return -ENOMEM;
}

static int __init chardev_init(void)
{
        int ret = -1;

        cachep = kmem_cache_create("chardev_kmem", 40, 0, SLAB_HWCACHE_ALIGN, NULL, NULL);
        if (!cachep)
                goto out;

        ret = alloc_chrdev_region(&devno, 0, 1, DEVICE_NAME);
        if (ret < 0)
                goto region_err;

        cdevp = cdev_alloc();
        if (!cdevp)
                goto alloc_err;

        cdev_init(cdevp, &chardev_fops);
        ret = cdev_add(cdevp, devno, 1);
        if (!ret)
                goto out;

        cdev_del(cdevp);
        cdevp = NULL;
alloc_err:
        unregister_chrdev_region(devno, 1);
        devno = -1;
region_err:
        kmem_cache_destroy(cachep);
        cachep = NULL;
out:
        return ret;
}

static void __exit chardev_exit(void)
{
        if (cdevp)
                cdev_del(cdevp);

        if (devno != -1)
                unregister_chrdev_region(devno, 1);

        if (cachep)
                kmem_cache_destroy(cachep);
}

MODULE_LICENSE("GPL");

module_init(chardev_init);
module_exit(chardev_exit);