Messages in this thread | | | Date | Wed, 8 May 2013 09:55:45 +0800 | From | Wang YanQing <> | Subject | Re: [PATCH]TTY: Fix tty can't be restarted by TCXONC ioctl request |
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On Tue, May 07, 2013 at 11:58:00AM -0700, Greg KH wrote: > On Wed, May 08, 2013 at 02:47:34AM +0800, Wang YanQing wrote: > > The reason is before emacs takeover control the tty, > > we use CTRL-S to XOFF it. Then when emacs takeover the > > control, it may don't use the flow-control, so emacs hang. > > But after search the emacs's startup codes, I find they use TCXONC > > to workaround this situation: > > > > /* This code added to insure that, if flow-control is not to be used, > > we have an unlocked terminal at the start. */ > > if (!tty_out->flow_control) ioctl (fileno (tty_out->input), TCXONC, 1); > > ioctl (fileno (tty_out->input), TCXONC, 1);
The second line of ioctl: "ioctl (fileno (tty_out->input), TCXONC, 1);"
It is not there in emacs' code, I add it for debuging, and forget to delete it. Greg KH, could you delete it from ChangeLog if you accept this patch?
> > But this workaround never work due the kernel's current code. > > This patch fix it. > > > > Below is the ChangeLog introduce the tty->flow_stopped flag: > > > > Thu Nov 21 10:05:22 1996 Theodre Ts'o <tytso@localhost.mit.edu> > > > > * tty_ioctl.c (tty_wait_until_sent): Always check the driver > > wait_until_ready routine, even if there are no characters > > in the xmit buffer. (There may be charactes in the device > > FIFO.) > > (n_tty_ioctl): Add new flag tty->flow_stopped which > > indicates whether the tty is stopped due to a request by > > the TCXONC ioctl (used by tcflow). If so, don't let an > > incoming XOFF character restart the tty. The tty can only > > be restarted by another TCXONC request. > > > > So I think this patch make TCXONC can restart tty which stopped by > > STOP_CHAR don't break the original meaning. > > > > This patch will fix some strange tty relation hang problem, > > I believe I meet it with vim in ssh, and also see below bug report: > > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=465823 > > So this has been a problem since 1996? Or is it newly introduced due to > some changes in this area in a newer kernel?
I have tested the v2.6.32.45, and have the same issue, my current environment can't compile and test v2.6.24/v2.6.25, due make version maybe.
But after explore history codes, I want to say, yes, this issue since 1996 that we can't use TCXONC to restart tty which be stopped by STOP_CHAR.
Kernel process the STOP_CHAR/START_CHAR to implement flow control, but userspace should have methold to START/STOP it by ioctl or others' similar positive method which don't depend on another side, that's TCXONC.
According http://en.wikibooks.org/wiki/Serial_Programming/termio
" TCXONC Start or stop the output. "
Thanks.
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