and NBD use it to access storage services provided by Curve. The client provids posix-like interface, such as read/write/aioread/aiowrite in data plane and open/create/rename/extend, etc in control will call the function that we pass in through the user state machine to complete the disk write operation. CurveFS architecture Curvefs implements the file system interface based on FUSE.

{ OK = 0; // UNKNOWN_ERROR = 1; // NOSPACE = 2; // } // fs interface message GetFsInfoRequest { optional uint32 fsId = 1; // fs id optional string fsName DeleteFsInfoResponse { required MetaStatusCode statusCode = 1; } service MdsService { // fs interface rpc CreateFs(CreateFsRequest) returns (CreateFsResponse); rpc MountFs(MountFsRequest) returns OK = 0; // UNKNOWN_ERROR = 1; // NOSPACE = 2; // } // dentry interface© XXX Page 7 of 15 message GetDentryRequest { required uint32 fsId = 1; required uint64

即使文件/目录已经被另一个进程删除了（nlink==0） 这样的语义。 这部分内容在fuse的相关接口中也有描述如下： /** * Forget about an inode * * This function is called when the kernel removes an inode * from its internal caches. * * The inode's lookup removal of the inode * until the lookup count reaches zero (see description of the * forget function). * * Valid replies: * fuse_reply_err * * @param req request handle * @param parent removal of the * inode until the lookup count reaches zero (see description * of the forget function). *© XXX Page 6 of 15 * Valid replies: * fuse_reply_err * * @param req request handle

CurveFS can manage different storages (HDFS, OSS, EBS) below • Apps access data by POSIX interface • Infrequent data is moved to OSS, and frequent data is moved to high speed storage transparentlyData

SpaceStatusCode status = 1; // required uint64 chunkId = 2; } service SpaceAllocService { // space interface rpc InitSpace(InitSpaceRequest) returns (InitSpaceResponse); rpc AllocateSpace(AllocateSpaceRequest)

unique: 69, error: -38 (Function not implemented), outsize: 16 unique: 70, opcode: SETXATTR (21), nodeid: 2, insize: 116, pid: 2081159 unique: 70, error: -38 (Function not implemented), outsize: