Mail Archives: opendos/1997/02/09/10:28:37
> > Hmm, there is an interesting question. If filesystem support is loaded
> > from CONFIG.SYS, and you want to have a 100% VFAT or even ext2fs
> > filesystem, how will DOS be able to read the filesystem to find CONFIG.SYS
> > so that it can load the file system driver that is required to read things
> > from the filesystem that CONFIG.SYS is held on....
>
> The root filesystem type will HAVE to be compiled into the kernel
> directly, otherwise how can ANY files be read off of it? Other
> filesystems may either be "built in", or can be added via boot
> time commands or loaded on the fly with some kind of module
> loader. (Preferably one that resides in XMS :o)
Not quite so, IMHO. Think about how are IBMDOS.COM and IBMBIO.COM loaded at
boot time? Neither MBR nor BR code knows anything about the file system. The
physical location of these files on the disk is know at the format time and
hard-coded into the BR code. To allow mounting *any* FS as the root *without
the need to compile any driver into the kernel* one should only know location
of the superblock on the disk. During the partition formatting, user selects
which file systems may be used as root and the formatter allocates enough
space in the superblock to store all the drivers, mount table (config file)
and map of the driver modules stored in the superblock. Now, the code stored
in BR reads the mount table and the map, finds which driver is to be loaded
and then reads in and executes the system image (which might be stored in the
superblock as well), Should the code be too big to fit in the BR, a system
loader may be stored in the superblock.
In this setup user may shuffle the root FS changing between all the drivers
stored in superblock. BTW. I think that superblock is a good idea to protect
the kernel from a too inquisitive, yet unexperienced, user.
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