The TTY driver now respects the ICANON flag, enabling basic line
editing like VKILL, VERASE, VEOF and VWERASE. Additionally,
ICANON is now set by default.
Basic echoing has can now be enabled via the ECHO flag, though
more complicated echoing like ECHOCTL or ECHONL has not been
implemented.
TTY::emit is called from an IRQ handler, and is used to push input data
into a buffer for later retrieval. Previously this was using DoubleBuffer,
but that class wants to take a lock. Our lock code wants to make sure
interrupts are enabled, but they're disabled while an IRQ handler is
running. This made the kernel sad, but this CircularQueue cheers it up by
avoiding the lock requirement completely.
After reading a bunch of POSIX specs, I've learned that a file descriptor
is the number that refers to a file description, not the description itself.
So this patch renames FileDescriptor to FileDescription, and Process now has
FileDescription* file_description(int fd).
