我们通过开发一个新操作系统需要的步骤，来切入学习smb client。
dentry操作方法。file操作方法，常规文件、目录、快速符号链接、普通符号链接、其他类型。address_space操作方法，常规文件、其他类型。注意，我只会列出结构体的代码，会在结构的成员加些中文注释（也可能以后再加），不会贴整段的函数代码，因为函数的实现要自己去看，看具体问题时再看函数实现才有意义。
由于smb client没有磁盘超级块，所以只有内存超级块结构体，在cifs_set_super()函数中赋值sb->s_fs_info = mnt_data->cifs_sb。
struct cifs_sb_info {
struct rb_root tlink_tree; // tlink 树
spinlock_t tlink_tree_lock; // tlink 树锁
struct tcon_link *master_tlink; // 主 tlink
struct nls_table *local_nls; // 本地 nls 表
struct smb3_fs_context *ctx; // smb3 文件系统上下文
atomic_t active; // 活跃计数
unsigned int mnt_cifs_flags; // 挂载标志
struct delayed_work prune_tlinks; // 延迟清理 tlinks
struct rcu_head rcu; // RCU 头
/* 只有当 CIFS_MOUNT_USE_PREFIX_PATH 被设置时使用 */
char *prepath; // 预路径
/*
* 指示是否在以后关闭了 serverino 选项
* (cifs_autodisable_serverino) 以匹配新挂载点。
*/
bool mnt_cifs_serverino_autodisabled; // serverino 自动禁用标志
/*
* 挂载完成后可用。
*/
struct dentry *root; // 根目录 dentry
}; static const struct super_operations cifs_super_ops = {
.statfs = cifs_statfs,
.alloc_inode = cifs_alloc_inode,
.write_inode = cifs_write_inode,
.free_inode = cifs_free_inode,
.drop_inode = cifs_drop_inode,
.evict_inode = cifs_evict_inode,
/* .show_path = cifs_show_path, */ /* 我们是否需要显示路径？ */
.show_devname = cifs_show_devname,
/* .delete_inode = cifs_delete_inode, */ /* 除非以后我们添加惰性关闭
索引节点的功能，或者内核忘记在关闭时调用我们与打开次数相同的
释放次数，否则不需要上述函数 */
.show_options = cifs_show_options,
.umount_begin = cifs_umount_begin,
.freeze_fs = cifs_freeze,
#ifdef CONFIG_CIFS_STATS2
.show_stats = cifs_show_stats,
#endif
}; smb没有磁盘索引节点，只有内存索引节点。
/*
* 每个文件 inode 的结构体
*/
struct cifsInodeInfo {
struct netfs_inode netfs; /* Netfslib 上下文和 vfs inode */
bool can_cache_brlcks; // 是否可以缓存字节范围锁
struct list_head llist; /* 该 inode 持有的锁列表 */
/*
* 注意: 有些代码路径会两次调用 down_read(lock_sem)，所以
* 我们必须始终使用 cifs_down_write() 而不是 down_write()
* 来避免此信号量的死锁。
*/
struct rw_semaphore lock_sem; /* 保护上面的字段 */
/* BB 添加用于脏页列表，即 oplock 的写缓存信息 */
struct list_head openFileList; // 打开文件列表
spinlock_t open_file_lock; /* 保护 openFileList */
__u32 cifsAttrs; /* 例如 DOS 归档位、稀疏、压缩、系统等属性 */
unsigned int oplock; /* 我们拥有的 oplock/lease 级别 */
unsigned int epoch; /* 用于跟踪租约状态变化 */
#define CIFS_INODE_PENDING_OPLOCK_BREAK (0) /* 正在进行 oplock 断裂 */
#define CIFS_INODE_PENDING_WRITERS (1) /* 正在进行写操作 */
#define CIFS_INODE_FLAG_UNUSED (2) /* 未使用的标志 */
#define CIFS_INO_DELETE_PENDING (3) /* 服务器上待删除 */
#define CIFS_INO_INVALID_MAPPING (4) /* pagecache 无效 */
#define CIFS_INO_LOCK (5) /* 同步锁位 */
#define CIFS_INO_MODIFIED_ATTR (6) /* 指示 mtime/ctime 的变化 */
#define CIFS_INO_CLOSE_ON_LOCK (7) /* 不要在设置锁时延迟关闭 */
unsigned long flags; // 标志字段
spinlock_t writers_lock; // 写入锁
unsigned int writers; /* 此 inode 的写入者数量 */
unsigned long time; /* inode 最后更新的 jiffies */
u64 server_eof; /* 服务器上的当前文件大小 - 由 i_lock 保护 */
u64 uniqueid; /* 服务器 inode 编号 */
u64 createtime; /* 服务器上的创建时间 */
__u8 lease_key[SMB2_LEASE_KEY_SIZE]; /* 此 inode 的租约密钥 */
struct list_head deferred_closes; /* 延迟关闭列表 */
spinlock_t deferred_lock; /* 保护延迟列表 */
bool lease_granted; /* 标志指示是否授予租约或 oplock。 */
char *symlink_target; // 符号链接目标
}; const struct inode_operations cifs_file_inode_ops = {
.setattr = cifs_setattr,
.getattr = cifs_getattr,
.permission = cifs_permission,
.listxattr = cifs_listxattr,
.fiemap = cifs_fiemap,
.get_acl = cifs_get_acl,
.set_acl = cifs_set_acl,
}; const struct inode_operations cifs_dir_inode_ops = {
.create = cifs_create,
.atomic_open = cifs_atomic_open,
.lookup = cifs_lookup,
.getattr = cifs_getattr,
.unlink = cifs_unlink,
.link = cifs_hardlink,
.mkdir = cifs_mkdir,
.rmdir = cifs_rmdir,
.rename = cifs_rename2,
.permission = cifs_permission,
.setattr = cifs_setattr,
.symlink = cifs_symlink,
.mknod = cifs_mknod,
.listxattr = cifs_listxattr,
.get_acl = cifs_get_acl,
.set_acl = cifs_set_acl,
}; const struct inode_operations cifs_symlink_inode_ops = {
.get_link = cifs_get_link,
.permission = cifs_permission,
.listxattr = cifs_listxattr,
}; static const struct inode_operations cifs_ipc_inode_ops = {
.lookup = cifs_lookup,
};
const struct inode_operations cifs_namespace_inode_operations = {
}; dentry操作const struct dentry_operations cifs_dentry_ops = {
.d_revalidate = cifs_d_revalidate,
.d_automount = cifs_d_automount,
/* d_delete: cifs_d_delete, */ /* 除了调试之外不需要 */
};
const struct dentry_operations cifs_ci_dentry_ops = {
.d_revalidate = cifs_d_revalidate,
.d_hash = cifs_ci_hash,
.d_compare = cifs_ci_compare,
.d_automount = cifs_d_automount,
}; file操作const struct file_operations cifs_file_ops = {
.read_iter = cifs_loose_read_iter,
.write_iter = cifs_file_write_iter,
.open = cifs_open,
.release = cifs_close,
.lock = cifs_lock,
.flock = cifs_flock,
.fsync = cifs_fsync,
.flush = cifs_flush,
.mmap = cifs_file_mmap,
.splice_read = filemap_splice_read,
.splice_write = iter_file_splice_write,
.llseek = cifs_llseek,
.unlocked_ioctl = cifs_ioctl,
.copy_file_range = cifs_copy_file_range,
.remap_file_range = cifs_remap_file_range,
.setlease = cifs_setlease,
.fallocate = cifs_fallocate,
};
const struct file_operations cifs_file_strict_ops = {
.read_iter = cifs_strict_readv,
.write_iter = cifs_strict_writev,
.open = cifs_open,
.release = cifs_close,
.lock = cifs_lock,
.flock = cifs_flock,
.fsync = cifs_strict_fsync,
.flush = cifs_flush,
.mmap = cifs_file_strict_mmap,
.splice_read = filemap_splice_read,
.splice_write = iter_file_splice_write,
.llseek = cifs_llseek,
.unlocked_ioctl = cifs_ioctl,
.copy_file_range = cifs_copy_file_range,
.remap_file_range = cifs_remap_file_range,
.setlease = cifs_setlease,
.fallocate = cifs_fallocate,
};
const struct file_operations cifs_file_direct_ops = {
.read_iter = cifs_direct_readv,
.write_iter = cifs_direct_writev,
.open = cifs_open,
.release = cifs_close,
.lock = cifs_lock,
.flock = cifs_flock,
.fsync = cifs_fsync,
.flush = cifs_flush,
.mmap = cifs_file_mmap,
.splice_read = copy_splice_read,
.splice_write = iter_file_splice_write,
.unlocked_ioctl = cifs_ioctl,
.copy_file_range = cifs_copy_file_range,
.remap_file_range = cifs_remap_file_range,
.llseek = cifs_llseek,
.setlease = cifs_setlease,
.fallocate = cifs_fallocate,
};
const struct file_operations cifs_file_nobrl_ops = {
.read_iter = cifs_loose_read_iter,
.write_iter = cifs_file_write_iter,
.open = cifs_open,
.release = cifs_close,
.fsync = cifs_fsync,
.flush = cifs_flush,
.mmap = cifs_file_mmap,
.splice_read = filemap_splice_read,
.splice_write = iter_file_splice_write,
.llseek = cifs_llseek,
.unlocked_ioctl = cifs_ioctl,
.copy_file_range = cifs_copy_file_range,
.remap_file_range = cifs_remap_file_range,
.setlease = cifs_setlease,
.fallocate = cifs_fallocate,
};
const struct file_operations cifs_file_strict_nobrl_ops = {
.read_iter = cifs_strict_readv,
.write_iter = cifs_strict_writev,
.open = cifs_open,
.release = cifs_close,
.fsync = cifs_strict_fsync,
.flush = cifs_flush,
.mmap = cifs_file_strict_mmap,
.splice_read = filemap_splice_read,
.splice_write = iter_file_splice_write,
.llseek = cifs_llseek,
.unlocked_ioctl = cifs_ioctl,
.copy_file_range = cifs_copy_file_range,
.remap_file_range = cifs_remap_file_range,
.setlease = cifs_setlease,
.fallocate = cifs_fallocate,
};
const struct file_operations cifs_file_direct_nobrl_ops = {
.read_iter = cifs_direct_readv,
.write_iter = cifs_direct_writev,
.open = cifs_open,
.release = cifs_close,
.fsync = cifs_fsync,
.flush = cifs_flush,
.mmap = cifs_file_mmap,
.splice_read = copy_splice_read,
.splice_write = iter_file_splice_write,
.unlocked_ioctl = cifs_ioctl,
.copy_file_range = cifs_copy_file_range,
.remap_file_range = cifs_remap_file_range,
.llseek = cifs_llseek,
.setlease = cifs_setlease,
.fallocate = cifs_fallocate,
}; const struct file_operations cifs_dir_ops = {
.iterate_shared = cifs_readdir,
.release = cifs_closedir,
.read = generic_read_dir,
.unlocked_ioctl = cifs_ioctl,
.copy_file_range = cifs_copy_file_range,
.remap_file_range = cifs_remap_file_range,
.llseek = generic_file_llseek,
.fsync = cifs_dir_fsync,
}; address_space操作const struct address_space_operations cifs_addr_ops = {
.read_folio = cifs_read_folio,
.readahead = cifs_readahead,
.writepages = cifs_writepages,
.write_begin = cifs_write_begin,
.write_end = cifs_write_end,
.dirty_folio = cifs_dirty_folio,
.release_folio = cifs_release_folio,
.direct_IO = cifs_direct_io,
.invalidate_folio = cifs_invalidate_folio,
.launder_folio = cifs_launder_folio,
.migrate_folio = filemap_migrate_folio,
/*
* TODO: 调查一下，如果有用，我们可以添加一个 is_dirty_writeback
* 辅助函数（如果需要的话）
*/
.swap_activate = cifs_swap_activate,
.swap_deactivate = cifs_swap_deactivate,
};
/*
* cifs_readahead 需要服务器支持一个足够大的缓冲区，以容纳
* 头部加上一个完整的数据页。否则，我们需要在地址空间操作中
* 省略 cifs_readahead 。
*/
const struct address_space_operations cifs_addr_ops_smallbuf = {
.read_folio = cifs_read_folio,
.writepages = cifs_writepages,
.write_begin = cifs_write_begin,
.write_end = cifs_write_end,
.dirty_folio = cifs_dirty_folio,
.release_folio = cifs_release_folio,
.invalidate_folio = cifs_invalidate_folio,
.launder_folio = cifs_launder_folio,
.migrate_folio = filemap_migrate_folio,
}; struct file_system_type cifs_fs_type = {
.owner = THIS_MODULE,
.name = "cifs",
.init_fs_context = smb3_init_fs_context,
.parameters = smb3_fs_parameters,
.kill_sb = cifs_kill_sb,
.fs_flags = FS_RENAME_DOES_D_MOVE,
};
struct file_system_type smb3_fs_type = {
.owner = THIS_MODULE,
.name = "smb3",
.init_fs_context = smb3_init_fs_context,
.parameters = smb3_fs_parameters,
.kill_sb = cifs_kill_sb,
.fs_flags = FS_RENAME_DOES_D_MOVE,
}; init_cifs()和exit_cifs()。