Question on tty line discipline

Question on tty line discipline

[Christopher Meller]

Hi,

I have a question concerning the line discipline behaviour for serial
devices.
When the line discipline is set via ioctl from  user space to e.g. N_PPP and the userspace program returns without resetting  the line discipline back to N_TTY, the serial device cannot be used (ENODV) until an appropriate  ioctl (to N_TTY) is performed. Is there any reason for the fact that the line discipline is not reset by the kernel , when closing the device. 

Could you please CC me on answers and comments ?


Kind regards,

Christopher Meller



-- 
Christopher Meller
Software engineer

Innominate Security Technologies AG
protecting industrial networks
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Re: Question on tty line discipline

[Alan]

On Wed, 28 Feb 2007 14:47:12 +0100
Christopher Meller <cmeller@innominate.com> wrote:

> Hi,
> 
> I have a question concerning the line discipline behaviour for serial
> devices.
> When the line discipline is set via ioctl from  user space to e.g. N_PPP and the userspace program returns without resetting  the line discipline back to N_TTY, the serial device cannot be used (ENODV) until an appropriate  ioctl (to N_TTY) is performed. Is there any reason for the fact that the line discipline is not reset by the kernel , when closing the device. 

No special reason, it has simply always been that way. Getty and friends
are expected to put the tty back into a sane state.

Re: Question on tty line discipline

[Tilman Schmidt]

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Am 28.02.2007 14:47 schrieb Christopher Meller:
> When the line discipline is set via ioctl from  user space to e.g. N_PPP and the userspace program returns without resetting  the line discipline back to N_TTY, the serial device cannot be used (ENODV) until an appropriate  ioctl (to N_TTY) is performed. Is there any reason for the fact that the line discipline is not reset by the kernel , when closing the device. 

Is that really so? While testing a line discipline I have written
myself (N_GIGASET_M101) I came to the opposite conclusion.

Specifically, when I set the line discipline on eg. /dev/ttyS1 to
N_GIGASET_M101 from the user space daemon I have written for that
purpose, and that user space daemon exits, my line discipline is
removed, ie. its .close method is called. That is true even if I
kill the user space daemon by sending it an uncaught signal.

-- 
Tilman Schmidt                          E-Mail: tilman@imap.cc
Bonn, Germany
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