So to implement notifications on top of pipes, I've hacked it together a bit
in the following ways:
(1) I'm passing O_TMPFILE to the pipe2() system call to indicate that you
want a notifications pipe. This prohibits splice and co. from being
called on it as I don't want to have to try to fix iov_iter_revert() to
handle kernel notifications being intermixed with splices.
The choice of O_TMPFILE was just for convenience, but it needs to be
something different. I could, for instance, add a constant,
O_NOTIFICATION_PIPE with the same *value* as O_TMPFILE. I don't think
it's likely that it will make sense to use O_TMPFILE with a pipe, but I
also don't want to eat up another O_* constant just for this.
Unfortunately, pipe2() doesn't have any other arguments into from which I
can steal a bit.
(2) I've added a pair of ioctls to configure the notifications bits. They're
ioctls as I just reused the ioctl code from my devmisc driver. Should I
use fcntl() instead, such as is done for F_SETPIPE_SZ?
The ioctls do two things: set the ring size to a number of slots (so
similarish to F_SETPIPE_SZ) and set filters.
Any thoughts on how better to represent these bits?
Thanks,
David
