mb2mfs – Multiboot2-Module File System¶

The Multiboot2-Module file system provides Multiboot2 modules as files.

This file system is implemented in

This filesystem provides multiboot2 modules as files.

General Information ¶

Using the Multiboot2 boot protocol, one can specify modules to be loaded into memory during boot. The module’s name – as specified, e.g., in grub.cfg – serves as the file’s absolute path name inside the file system.

Example snippet for grub.cfg:

menuentry "tomOSii" {
        multiboot2 /boot/tomOSii.bin
        module2 /boot/sbin/init/init.bin /sbin/init
        boot
}

In the above snippet, the kernel image is loaded from /boot/tomOSii.bin on the boot volume. A single module is loaded from /boot/sbin/init/init.bin on the boot volume into memory. The name /sbin/init is assigned to the module. This name serves as the path to the respective file provided by the Multiboot2-Module file system. The file’s content is identical to the content of /boot/sbin/init/init.bin. If mb2mfs is mounted to /, then the file is available as /sbin/init.

Initialization ¶

The file system driver is initialized by calling

void fs_mb2mfs_init(void)¶

Initialize the multiboot2-module filesystem.

Register the multiboot2-module filesystem to the filesystem core.

Mounting the File System ¶

A Multiboot2-module file system is mounted by calling the mount operation via the mount system call.

For this file system to work, users will have to provide a pointer to the Multiboot2 info struct as mount data.

The mount operation is implemented in

static inode_t *__fs_mb2mfs_mount(file_system_t *fs, int flags, const char *device, void *data)¶

Mount the file system.

Parameters:

fs – The file system to be mounted
flags – The mount flags – have to be MS_NOT_YET_IMPLEMENTED
device – The device the file system lives on – unused here
data – Additional data – unused here

Looking Up a File ¶

A file, i.e., a multiboot2 module, is looked up by using the lookup operation:

static inode_t *__fs_mb2mfs_lookup(inode_t *dir, const char *name, unsigned int flags)¶

Look up an inode for a path /p name.

Parameters:

dir – The inode representing the file system root
name – The full path of the file to be looked up
flags – unused

Returns:

the inode, on success

Returns:

NULL, on failure

Opening a File ¶

A file, i.e., a multiboot2 module, is opened by using the open operation:

static int __fs_mb2mfs_fops_open(inode_t *inode, file_t *file)¶

Open a multiboot2 module as a file.

There is nothing to be done here. The required steps are already handelled by sys_open.

Returns:: 0

Closing a File ¶

A file, i.e., a multiboot2 module, is closed by using the open operation:

static int __fs_mb2mfs_fops_close(inode_t *inode, file_t *file)¶

Close a multiboot2 module as a file.

There is nothing to be done here. The required steps are already handelled by sys_close.

Returns:: 0

Reading from a File ¶

Reading from a file, i.e., a multiboot2 module, is facilitated by the read operation:

static ssize_t __fs_mb2mfs_fops_read(file_t *file, char *buffer, size_t buffer_size, size_t *offset)¶

Read from a multiboot2 module.

Parameters:

file – The file to read from
buffer – The buffer to read into
buffer_size – The size of the buffer / the number of bytes to read
offset – Pointer to the offset specifying where to start reading

Returns:

The number of bytes read, on success. May be less than buffer_size.

Returns:

0, if reading while already at the end of the file.