Messages in this thread | | | Date | Tue, 7 May 2013 19:02:00 -0700 | From | Greg KH <> | Subject | Re: [PATCH]TTY: Fix tty can't be restarted by TCXONC ioctl request |
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On Wed, May 08, 2013 at 09:55:45AM +0800, Wang YanQing wrote: > 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?
Yes, I can.
> > > 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. > "
What about Peter's comments on this patch?
thanks,
greg k-h
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