Very Computer

Hi there,

I'm getting into some operating system development, and it would make my
life a lot easier right now if I could use the Linux device drivers for
the time being to format my disks and such.

My question then becomes, how can I use /dev/fd0 directly?  I realise
I'd have to be root, that's no problem.  My understanding would be that
I can just open /dev/fd0 as a file and read and write to it.  I tried
this, but had some troubles.  I think I was reading correctly, but not
writting.

I know a "cat /dev/fd0" will give me the contents of the disk, so it
obviously acts as if it's a file, but it's actually a block device.
Does this mean that "fseek(file, 10, SEEK_SET)" will get me to the 10th
byte, or the 10th block?  If block, how do I find out the size (I'm
assuming it'd be 512 bytes, for a regular disk) of the block?

Any information on this topic would be helpfull.

Thanks,
Jeff

PS: Please respond via email if possible.

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|> I know a "cat /dev/fd0" will give me the contents of the disk, so it
|> obviously acts as if it's a file, but it's actually a block device.
|> Does this mean that "fseek(file, 10, SEEK_SET)" will get me to the 10th
|> byte, or the 10th block?

The offset will always be in bytes, for all types of files.  (Actually you
will get at the 11th byte, the first one being at offset 0.)

--
Andreas Schwab                                      "And now for something

Block size is irrelevant because you are dealing with a block
device, not a raw or character device. All block devices have
the same logical block size of one kilobyte, but this is
an implementation detail of the operating system that you
don't need to worry about.

Blocks don't necessarily correspond to physical sectors; they are a
logical entity defined by the buffer cache implementation.
When you write to the floppy, you are actually writing to the
system's buffer cache which will be flushed at some later time.

Block sizes do matter when you write to a raw character device
such as a tape drive, because then each read() or write() request
may be interpreted as writing or reading a new tape block.
The use of an incorrect block size can lead to blocks
that are partially filled, or worse, that are truncated.

This could never happen with a block device. You can write
one byte, or you can write a megabyte. In all cases, the
opearting system will properly execute the request and
update the appropriate buffers. The low-level driver will
then correctly write the modified buffers to the hardware
device.