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SubjectRe: [PATCH v4 1/9] tty: n_gsm: fix user open not possible at responder until initiator open
On Fri, Jul 01, 2022 at 08:16:44AM +0200, D. Starke wrote:
> From: Daniel Starke <>
> After setting up the control channel on both sides the responder side may
> want to open a virtual tty to listen on until the initiator starts an
> application on a user channel. The current implementation allows the
> open() but no other operation, like termios. These fail with EINVAL.
> The responder sided application has no means to detect an open by the
> initiator sided application this way. And the initiator sided applications
> usually expect the responder sided application to listen on the user
> channel upon open.
> Set the user channel into half-open state on responder side once a user
> application opens the virtual tty to allow IO operations on it.
> Furthermore, keep the user channel constipated until the initiator side
> opens it to give the responder sided application the chance to detect the
> new connection and to avoid data loss if the responder sided application
> starts sending before the user channel is open.
> Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
> Signed-off-by: Daniel Starke <>
> ---
> drivers/tty/n_gsm.c | 31 +++++++++++++++++++++++++++++--
> 1 file changed, 29 insertions(+), 2 deletions(-)
> Stable backport remark has been removed compared to v3. No other changes applied.
> Link:

Not all patches in this series would apply to my tree. Please rebase
the remaining ones and resend.


greg k-h

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