2010.02.12
Fixed two problems. Here's the comments in the code.
 *  I fixed two bugs. First, I accidently typed an index i in qbuf[i]
 *  in the put_user instead of the proper index qbuf[rp].
 *  Second, I fixed an infinite write loop that occurred when the
 *  buffer to write had a length greater than the circular buffer.
 *  This caused the caller to persistently call back waiting to
 *  hear that all of the buffer length of characters had been
 *  written to the device. To fix this I just lied and returned
 *  the caller's buffer length on write instead of the actual
 *  number of characters put into the device circular buffer.
 *  That fix is consistent with just throwing the characters
 *  away, although I should probably have returned
 *  a -EOVERFLOW error or something like that.

2010.02.11
It currently succeeds on write echo hi > ./dev/mydev
followed by cat ./dev/mydev.

It fails in an infinite loop on echo 123456789abcde > ./dev/mydev
The device_write goes into an infinite loop 
and the buffer conditions indicate the buffer has filled.
But it keeps trying to write. Why? Do I need to return something
to echo device write to indicate writing is done?

Also, it dumps tons of garbage to /var/log/syslog that
I just manually deleted. That means it is buffer overflowing.

2010.02.11
Generally got it performing some activities. I needed to
sort out the types ssize_t and size_t and I needed to
stop using 0 terminated string assumptions and move to
buffers with lengths. I needed to explicitly manage buffer
overflow checks. 

2010.02.08
I'm just getting started with this, now that I've finished
my circular buffer prototype in experiment 2. Sigh, it took
forever. 

2010.02.03
In this experiment, derived from experiment one, I want to provide
a device_write function that allows a user to put something into
the device that I'm creating. I'll allow the user to put stuff
into the device until the device is "full". I will be able
to read from the device but the read will return nothing if
the device is empty. 

I'll just have a simple circular character buffer. Each
write will append a sequence of characters and each read
will return a sequence of characters, removing them from
the buffer. When buffer pointers are equal the device
is empty. When write pointer catches the read pointer
less one then the buffer is full.

I should be able to cat characters into the device up to
the size of the device (the buffer size) and I should be
able to cat from the device to empty it. 

Note that this operates like a character FIFO, but is not
yet the Nutt lab 10 because the readers and writers do
not block. Also, I'm only doing one FIFO.

I also don't plan on writing test programs in C. I'll just
use cat on the command line to write and read from the
file. Note that I think the regular cat >mydev will act
like a cat >>mydev. On the other hand, cat mydev will
empty the entire device and I won't get to see a partial
read. Maybe I'll write a get.c function that lets me
read just n characters.