For any particular partition, it is presumed that only one of the normal filesystems such as FAT, FFS, or ext2fs can be used, so there is a switch table managed by the functions in `disk_io.c'. The notation is that you can only mount one at a time.
The blocklist filesystem has a special place in the system. In addition to the normal filesystem (or even without one mounted), you can access disk blocks directly (in the indicated partition) via the blocklist notation. Using the blocklist filesystem doesn't effect any other filesystem mounts.
The variables which can be read by the filesystem backend are:
current_drive
current_partition
current_slice
saved_drive
saved_partition
part_start
part_length
print_possibilities
dir
function should print the possible completions
of a file, and false when it should try to actually open a file of that
name.
FSYS_BUF
The variables which need to be written by a filesystem backend are:
filepos
filemax
disk_read_func
NULL
at all other times (it will be
NULL
by default). If this isn't done correctly, then the
testload
and install
commands won't work
correctly.
The functions expected to be used by the filesystem backend are:
devread
grub_read
grub_read
can be used, after setting block_file
to 1.
The functions expected to be defined by the filesystem backend are described at least moderately in the file `filesys.h'. Their usage is fairly evident from their use in the functions in `disk_io.c', look for the use of the fsys_table array.
Caution: The semantics are such that then `mount'ing the filesystem, presume the filesystem buffer FSYS_BUF is corrupted, and (re-)load all important contents. When opening and reading a file, presume that the data from the `mount' is available, and doesn't get corrupted by the open/read (i.e. multiple opens and/or reads will be done with only one mount if in the same filesystem).
Go to the first, previous, next, last section, table of contents.