Bluejay Filesystem

Filesystem drivers are still a work in progress. To test a file system you will want to create and mount a virtual block device. The makefile in src/kernel will generate an hd0_ext2.img EXT2 disk image for you automatically. The default size is 32 megabytes, but you can create your own of any size if you want. Once the image has been created it will be loaded by QEMU automatically.

In order to write to the virtual hard disk from your host operating system you should mount it. The make mount command in src/kernel mount the image to $(BLUEJAY_ROOT)/mnt. If you are using an EXT2 filesystem you should probably change the owner of that directory once it is mounted so that you can write to it.

Virtual Filesystem

The Bluejay VFS is heavily inspired by UNIX. It relies on inodes and a tree of file nodes. The source can be found in src/kernel/vfs.c. This also exports a very low-level API for dealing with files – including the usual read(), write(), readdir(), etc – but this should not be used for much longer. A high level API utilizing file descriptors will be implemented to make this simpler.

Filesystem Drivers

The current filesystem driver(s) available in Bluejay are:

  • ext2
    • Read-only support, write support is in progress

Creating a Virtual Drive in QEMU

By default make qemu will load hd0_$(FS).img as the virtual hard drive for Bluejay. FS defaults to ext2 but can be set in your Jmk.options to any value. If this file does not exist it will be created using mkfs.$(FS), ie mkfs.ext2 by default. The default size of the file system is 35 megabytes, although you can create one of any size manually if you want. 35 megabytes is plenty for testing though.

The make mount command will mount the current virtual hard drive in $(ROOT)/mnt (where $(ROOT) is the root directory of the Bluejay sources, not /). This command requires superuser privileges. If you want to give your (host) user account write permissions use chown -R user:group /path/to/mnt where user and group are the user and group you want to own the files.

Currently Bluejay ignores file permissions so it doesn’t matter who you set the owner to.