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Changed the type for block addresses from size_t to uint16_t.
Added the '%c' conversion specifier to vsprintf(), so that it can now
output individual characters passed as arguments.
Added a an errno.h header containing a list of commonly used error
codes, as well as a basic strerror() routine to fetch corresponding
human-readable strings from a table.
Implemented barebones floppy driver. Currently lacking many (essential)
features, see TODO notes in floppy.c for more details.
Buffer structs now have a b_present flag to indicate whether or not the
data section is populated, as well as a b_wait element, as a queue for
any tasks waiting on the buffer. All tasks waiting on a block wait in
this queue, however, the task that originally called the driver to read,
may wait in a separate queue maintained by the driver. This system may
change in the future, and will likely depend on how head scheduling is
implemented in the driver.
The buffer_get_block() routine is now publically available in
kernel/fs.h. It can be called to retrieve a block from the buffer cache
(if readily available), or from the specified block device otherwise.
This routine returns a pointer to the buffer containing the cache.
The block_read() function now passes arguments and return values to the
floppy driver regardless of the device specified. The block_write()
function now indicates an error condition by setting b_device to zero in
the allocated buffer structure, as no devices with write functionality
currently exist. This behaviour will be updated in future, as more block
devices are added.
The mount_root() function has been modified to call buffer_get_block(),
instead of calling block_read() directly. As of now, nothing should call
block_read() or block_write() directly, as those functions are intended
for use by the buffer subsystem only.
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after hd_init() failed (on a system without a disk), would hang. Now,
hd_read_block() will fail if no hard disk is present on the system (as
indicated by the nblocks count being equal to zero). The same fix also
applies to the hd_write_block() function.
The hd_init() function now returns a status indicating either successful
drive detection and initialization, or failure. This return status won't
likely be needed due to the above bug-fix, but may prove useful in the
future.
Added framework for a block buffer subsystem. This subsystem uses
pre-allocated memory to cache blocks that are requested from the block
device subsystem. Cached blocks are stored on a linked list sorted in
order of usage frequency.
Modified the block read/write functions so that they no longer accept a
length parameter. The block I/O functions will only read or write a
single block at a time. If multiple blocks are required, multiple calls
will have to be made. This is to reduce complexity of block device
drivers and make integration with the new buffer subsystem easier.
Removed all calls to the ATA hard-disk driver. For now, it seems that
floppy media will be best as it allows for real-world hardware testing.
Furthermore, large portions of the hard-disk driver will need to be
re-written anyway once the block buffer subsystem is complete as it only
supports PIO transfers, whilst a buffer system will require DMA
transfers. As the hard-disk was previously the only supported block
device, the block device read/write functions will now always fail,
returning -1.
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