简单的文件系统

以下是一个简单的文件系统，该文件系统并没有实际的意义，只是为了帮助读者更好的理解文件系统的基本原理和工作的过程：

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/mount.h>
#include <linux/init.h>
#include <linux/namei.h>


#define AUFS_MAGIC 0x64668735

static struct vfsmount *aufs_mount;
static int aufs_mount_count;

static struct inode *aufs_get_inode(struct super_block *sb, int mode, dev_t dev)
{
    struct inode *inode = new_inode(sb);
    if (inode) {
    inode->i_mode = mode;
    inode->i_uid = current->fsuid;
    inode->i_gid = current->fsgid;
    inode->i_blksize = PAGE_CACHE_SIZE;
    inode->i_blocks = 0;
    inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;

    switch (mode & S_IFMT) {
    default:
        init_special_inode(inode, mode, dev);
        break;
    case S_IFREG:
        printk("creat a file \n");
        break;
    case S_IFDIR:
        inode->i_op = &simple_dir_inode_operations;
        inode->i_fop = &simple_dir_operations;
        printk("creat a dir file \n");
        inode->i_nlink++;
    break;
        }
    }
    return inode;
}

/* SMP-safe */
static int aufs_mknod(struct inode *dir, struct dentry *dentry,int mode, dev_t dev)
{
    struct inode *inode;
    int error = -EPERM;

    if (dentry->d_inode)
        return -EEXIST;
    inode = aufs_get_inode(dir->i_sb, mode, dev);
    if (inode) {
        d_instantiate(dentry, inode);
        dget(dentry);
        error = 0;
    }
    return error;
}

static int aufs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
    int res;

    res = aufs_mknod(dir, dentry, mode |S_IFDIR, 0);
    if (!res)
        dir->i_nlink++;
    return res;
}

static int aufs_create(struct inode *dir, struct dentry *dentry, int mode)
{
    return aufs_mknod(dir, dentry, mode | S_IFREG, 0);
}

static int aufs_fill_super(struct super_block *sb, void *data, int silent)
{
    static struct tree_descr debug_files[] = {{""}};
    return simple_fill_super(sb, AUFS_MAGIC, debug_files);
}
static struct super_block *aufs_get_sb(struct file_system_type *fs_type,int flags, const char *dev_name,void *data)
{
    return get_sb_single(fs_type, flags, data, aufs_fill_super);
}

static struct file_system_type au_fs_type = {
    .owner = THIS_MODULE,
    .name = "aufs",
    .get_sb = aufs_get_sb,
    .kill_sb = kill_litter_super,
};

static int aufs_create_by_name(const char *name, mode_t mode,struct dentry *parent,struct dentry **dentry)
{
    int error = 0;
/* If the parent is not specified, we create it in the root.
* We need the root dentry to do this, which is in the super
* block. A pointer to that is in the struct vfsmount that we
* have around.
*/
    if (!parent ) {
        if (aufs_mount && aufs_mount->mnt_sb) {
            parent = aufs_mount->mnt_sb->s_root;
                }
            }
    if (!parent) {
        printk("Ah! can not find a parent!\n");
        return -EFAULT;
        }
    *dentry = NULL;
    mutex_lock(&parent->d_inode->i_mutex);
    *dentry = lookup_one_len(name, parent, strlen(name));
    if (!IS_ERR(dentry)) {
        if ((mode & S_IFMT) == S_IFDIR)
            error = aufs_mkdir(parent->d_inode, *dentry, mode);
        else
            error = aufs_create(parent->d_inode, *dentry, mode);
    } else
        error = PTR_ERR(dentry);
        mutex_unlock(&parent->d_inode->i_mutex);
        return error;
}

struct dentry *aufs_create_file(const char *name, mode_t mode,struct dentry *parent, void *data,struct file_operations *fops)
{
    struct dentry *dentry = NULL;
    int error;
    printk("aufs: creating file '%s'\n",name);
    error = aufs_create_by_name(name, mode, parent, &dentry);

    if (error) {
        dentry = NULL;
        goto exit;
    }
    if (dentry->d_inode) {
        if (data)
            dentry->d_inode->u.generic_ip = data;
        if (fops)
            dentry->d_inode->i_fop = fops;
    }
    exit:
    return dentry;
}

struct dentry *aufs_create_dir(const char *name, struct dentry *parent)
{
    return aufs_create_file(name,S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,parent, NULL, NULL);
}

static int __init aufs_init(void)
{
    int retval;
    struct dentry *pslot;
    retval = register_filesystem(&au_fs_type);

    if (!retval) {
        aufs_mount = kern_mount(&au_fs_type);
        if (IS_ERR(aufs_mount)) {
            printk(KERN_ERR "aufs: could not mount!\n");
            unregister_filesystem(&au_fs_type);
            return retval;
        }
    }

    pslot = aufs_create_dir("woman star",NULL);
    aufs_create_file("lbb", S_IFREG | S_IRUGO, pslot, NULL, NULL);
    aufs_create_file("fbb", S_IFREG | S_IRUGO, pslot, NULL, NULL);
    aufs_create_file("ljl", S_IFREG | S_IRUGO, pslot, NULL, NULL);
    pslot = aufs_create_dir("man star",NULL);
    aufs_create_file("ldh", S_IFREG | S_IRUGO, pslot, NULL, NULL);
    aufs_create_file("lcw", S_IFREG | S_IRUGO, pslot, NULL, NULL);
    aufs_create_file("jw", S_IFREG | S_IRUGO, pslot, NULL, NULL);
    return retval;
}

static void __exit aufs_exit(void)
{
    simple_release_fs(&aufs_mount, &aufs_mount_count);
    unregister_filesystem(&au_fs_type);
}

module_init(aufs_init);
module_exit(aufs_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("This is a simple module");
MODULE_VERSION("Ver 0.1");