Re: [PATCH][RFC] kill TTY_DONT_FLIP

[Paul Fulghum <paulkf@microgate.com>]

Alan Cox wrote:
> Looks good to me on a first review.

I looked at the paths taken by n_tty_receive_buf()
for how they would effect read_chan():

* tty state (put_tty_queue,eraser,finish_erasing,etc)
* read wakeups
* start_tty/stop_tty
* put_char/opost

everything looks OK without TTY_DONT_FLIP

2.0.X relied on the BKL (and dinosaurs roamed the Earth)

2.1.X introduced TTY_DONT_FLIP to prevent read_chan and
n_tty_receive_buf from executing at the same time.

2.2.15 added tty->read_lock around the N_TTY read buffer,
which is the only thing needing protection in this context.

The usual progression to finer grained locking.
This looks like a safe removal.

The review also revealed a spot in reset_buffer_flags()
where tty->read_lock needs to be extended around
modifications of canon_head, canon_data, and read_flags.
I'll make a patch for that.

--
Paul Fulghum
Microgate Systems, Ltd.
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