Re: Is tty->receive_room no longer usable w/ SMP?

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2014-02-13, Peter Hurley <peter@hurleysoftware.com> wrote:
> On 02/13/2014 01:50 PM, Grant Edwards wrote:

>> For example, it turns out almost nobody on the planet uses IXANY. It
>> got left out of both our automated and manual regression testing, and
>> (embarassingly) it took 10+ years for somebody to realize that it
>> didn't work.  And that "somebody" was a customer that still had 2.4
>> kenels running in production machines.
>
> Not unusual. The N_TTY ldisc just had a bug fixed in 3.10 where
> turning off IXON with an already-stopped tty permanently hung the
> tty.

Yea, over the years, Xon/Xoff flow control is probably a larger source
of headaches than any other feature.  In fact, I think our serial core
drivers currently have to disable the UART's hardware Xon/Xoff
handling because the serial core API doesn't notify the driver when
the user makes a termios call to change the Xon/Xoff characters.  [Not
that anybody really uses that feature either...]

> We should extend the serial-core to add rx methods that work with
> your UARTs in their fastest and most native way. The idea behind
> serial-core is only to abstract the busy-work away from the i/o, not
> become an ill-fitting shoe that enforces The One True Way.

The prepare/push flip buffer API was pretty close to ideal.

It eliminates one set of buffer copy operations involved in the
room/insert/push method.  But, given the speed of in-memory buffer
copies, I doubt the difference is noticeable.

-- 
Grant Edwards               grant.b.edwards        Yow! for ARTIFICIAL
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