NaiveFS

Naive file system based on fuse.

About FUSE

• File System in Userspace: the most widely used user-space file system framework.
• Provides simple API and easy to understand its internal architecture and implementation details.
• FUSE's kernel module registers a fuse file-system driver and a /dev/fuse block device (like a shared space between user daemon and kernel module for exchanging requests and responses).
• VFS will route file requests from userspace to registered fuse kernel driver. The kernel driver allocates a FUSE request structure and puts it in a FUSE queue. Process wait for the request handled by user daemon of fuse. Processing the request might require re-entering the kernel again:
  • In our implementation, we have to handle requests by accessing virtual disk /dev/disk to simulate real file system driver. So one request from user processes will at least trap into kernel 3 times: 1. user process submits request; 2. fuse user daemon (our file system) handles virtual disk; 3. fuse user daemon submits response.
  • The user process will be suspended until all the processes above is finished.
  • Crash may happens at any point of these processes, so we need to manage consistency and persistency.
• User-kernel protocol:
  • handle requests from FUSE's kernel driver which have a direct mapping to traditional VFS operations;
  • Request structure:
    • type
    • sequence number
    • node ID: an unsigned 64-bit integer
• FUSE request queues:
  • interrupts: INTERRUPT,
  • forgets: FORGET (selected fairly with non-FORGET requests)
  • pending: synchronous requests (e.g., Metadata)
  • processing: the oldest pending request is moved to user space and the processing queue
  • background: asynchronous requests (read requests and write requests if the writeback cache is enabled)

Linux User API

TODO List

• A makefile for whole project. Thus we can run tests and build targets in different environments.

• FUSE operations:

  • Special：
    • INIT
    • DESTROY
  • Metadata:
    • OPEN
    • CREATE
    • STATFS
    • LINK
    • UNLINK
    • RELEASE
    • ACCESS
    • CHMOD
    • CHOWN
    • TRUNCATE
    • UTIMENS
    • RENAME
  • Data: (yfzcsc)
    • READ
    • WRITE
    • FLUSH
    • FSYNC
    • COPY_FILE_RANGE (not necessary)
    • WRITE_BUF (not necessary)
    • READ_BUF (not necessary)
  • Attributes: (yfzcsc)
    • GETATTR
    • SETATTR
  • Extended Attributes: (yfzcsc)
    • SETXATTR (not necessary)
    • GETXATTR (not necessary)
    • LISTXATTR (not necessary)
    • REMOVEXATTR (not necessary)
  • Symlinks: (yfzcsc)
    • SYMLINK
    • READLINK
  • Directory: (yfzcsc)
    • MKDIR
    • RMDIR
    • OPENDIR (not necessary)
    • RELEASEDIR (not necessary)
    • READDIR
    • FSYNCDIR (not necessary)
  • Locking:
    • LOCK
    • FLOCK
  • Misc: (yfzcsc)
    • BMAP
    • FALLOCATE
    • MKNOD
    • LOCTL
    • POLL

Run

bash run.sh