FUSE 内核实现代码分析（一） 初始化

基于linux-3.10内核

用户可以使用libfuse编写自己的文件系统，关键在于FUSE内核模块。做为实现用户空间文件系统的桥梁模块，还是很值得分析一下的。

USE Kernel模块由两部分组成：

第一部分——设备文件接口：fs/fuse/dev.c——回应io请求到/dev/fuse。fuse_dev_read()函数负责读出文件，并将来自“list of request”结构体的命令返回到调用函数。fuse_dev_write ()负责文件写入，并将写入的数据置放到“req→out”数据结构中。

第二部分——文件系统调用部分：fs/fuse/file.c，fs/fuse/inode.c，fs/fuse/dir.c——调用request_send()，将请求加入到“list of request”结构体中，等待回复(reply)。

第三部分——sysfs接口：fs/fuse/connect.c 对fuse一些简单控制和一些数据的导出。

[fs/fuse/inode.c]static int __init fuse_init(void){        int res;         printk(KERN_INFO "fuse init (API version %i.%i)\n",               FUSE_KERNEL_VERSION, FUSE_KERNEL_MINOR_VERSION);        INIT_LIST_HEAD(&fuse_conn_list);        res = fuse_fs_init();        if (res)                goto err;         res = fuse_dev_init();        if (res)                goto err_fs_cleanup;        res = fuse_sysfs_init();        if (res)                goto err_dev_cleanup;        res = fuse_ctl_init();        if (res)                goto err_sysfs_cleanup;        sanitize_global_limit(&max_user_bgreq);        sanitize_global_limit(&max_user_congthresh);        return 0; err_sysfs_cleanup:        fuse_sysfs_cleanup(); err_dev_cleanup:        fuse_dev_cleanup(); err_fs_cleanup:        fuse_fs_cleanup(); err:         return res;}

fuse_fs_init() 完成fuse_inode的kmem_cache的创建，注册fuse和fuseblk两种文件系统

static int __init fuse_fs_init(void){        int err;        fuse_inode_cachep = kmem_cache_create("fuse_inode",                                              sizeof(struct fuse_inode),                                              0, SLAB_HWCACHE_ALIGN,                                              fuse_inode_init_once);        err = -ENOMEM;        if (!fuse_inode_cachep)                goto out;        err = register_fuseblk();        if (err)                goto out2;        err = register_filesystem(&fuse_fs_type);        if (err)                goto out3;        return 0; out3:        unregister_fuseblk(); out2:        kmem_cache_destroy(fuse_inode_cachep); out:        return err;}

fuse_dev_init()完成fuse_request的kmem_cache的建仓，并注册/dev/fuse杂项设备，主设备号10，次设备号229

const struct file_operations fuse_dev_operations = {        .owner          = THIS_MODULE,        .llseek         = no_llseek,        .read           = do_sync_read,        .aio_read       = fuse_dev_read,        .splice_read    = fuse_dev_splice_read,        .write          = do_sync_write,        .aio_write      = fuse_dev_write,        .splice_write   = fuse_dev_splice_write,        .poll           = fuse_dev_poll,        .release        = fuse_dev_release,        .fasync         = fuse_dev_fasync,};EXPORT_SYMBOL_GPL(fuse_dev_operations);static struct miscdevice fuse_miscdevice = {        .minor = FUSE_MINOR,        .name  = "fuse",        .fops = &fuse_dev_operations,};              int __init fuse_dev_init(void){        int err = -ENOMEM;        fuse_req_cachep = kmem_cache_create("fuse_request",                                            sizeof(struct fuse_req),                                            0, 0, NULL);        if (!fuse_req_cachep)                goto out;                        err = misc_register(&fuse_miscdevice);        if (err)                goto out_cache_clean;                        return 0;         out_cache_clean:        kmem_cache_destroy(fuse_req_cachep); out:           return err;}

fuse_sysfs_init() 创建/sys/fs/fuse/connections目录

static int fuse_sysfs_init(void){        int err;                fuse_kobj = kobject_create_and_add("fuse", fs_kobj);        if (!fuse_kobj) {                err = -ENOMEM;                goto out_err;        }                       connections_kobj = kobject_create_and_add("connections", fuse_kobj);        if (!connections_kobj) {                err = -ENOMEM;                goto out_fuse_unregister;        }                return 0;         out_fuse_unregister:        kobject_put(fuse_kobj); out_err:        return err;}    

fuse_ctl_init() 注册fuse_ctl文件系统

int __init fuse_ctl_init(void){        return register_filesystem(&fuse_ctl_fs_type);} 

经过上面初始化，内核中多了以下东东，总结一下

1 现在内核了三种文件系统：fuse  fuseblk  fuse_ctl

2 与用户空间交互的设备接口 /dev/fuse

3 控制用的sysfs接口 /sys/fs/fuse