On 10/18/2010 4:18 PM, Christopher Faylor wrote:
On Mon, Oct 18, 2010 at 03:40:21PM -0400, Ken Brown wrote:
On 10/18/2010 2:34 PM, Christopher Faylor wrote:
On Sat, Oct 16, 2010 at 02:06:56PM -0400, Ken Brown wrote:
On 10/16/2010 1:17 PM, Ken Brown wrote:
I could use some help fixing a longstanding bug in the Cygwin build of
emacs, in which emacs is unable to send signals to subprocesses. A
symptom from the user's point of view is that one cannot interrupt a
process in shell mode by typing C-c C-c. I've found a workaround that
handles that case (SIGINT), as well as SIGQUIT and SIGTSTP. But as long
as I'm fixing this, I'd like to do it right and figure out how to handle
all signals.
This boils down to finding the right process group ID to pass to 'kill'.
On systems that have TIOCGPGRP, emacs uses the following code (in
src/process.c) to get this ID:
/* Return the foreground process group for the tty/pty that
the process P uses. */
static int
emacs_get_tty_pgrp (p)
struct Lisp_Process *p;
{
int gid = -1;
#ifdef TIOCGPGRP
if (ioctl (p->infd, TIOCGPGRP,&gid) == -1&& ! NILP (p->tty_name))
{
int fd;
/* Some OS:es (Solaris 8/9) does not allow TIOCGPGRP from the
master side. Try the slave side. */
fd = emacs_open (SDATA (p->tty_name), O_RDONLY, 0);
if (fd != -1)
{
ioctl (fd, TIOCGPGRP,&gid);
emacs_close (fd);
}
}
#endif /* defined (TIOCGPGRP ) */
return gid;
}
What's the right way to do this in Cygwin?
I guess it's clear from the context, but I should have said that the
problem only arises when emacs has to communicate with the subprocess
through a tty that is not the controlling tty of emacs. So tcgetpgrp()
doesn't work.
I am a little confused as to the difference between tcgetpgrp and
TIOCGPGRP given this man page description from "man 4 tty_ioctl" on
linux:
TIOCGPGRP pid_t *argp
When successful, equivalent to *argp = tcgetpgrp(fd).
Get the process group ID of the foreground process group on
this terminal.
TIOCSPGRP const pid_t *argp
Equivalent to tcsetpgrp(fd, *argp).
Set the foreground process group ID of this terminal.
Do you have a simple test case which demonstrates the difference between
the calls? It seems odd that TIOCGPGRP would allow more access to a tty
than tcgetpgrp.
The difference is that, according to POSIX, tcgetpgrp is required to
fail unless fd references the controlling terminal of the calling
process. Ironically, Cygwin's tcgetpgrp used to succeed in this
situation until Corinna fixed it a year ago:
http://www.cygwin.com/ml/cygwin-patches/2009-q4/msg00045.html
Yes, I got that but TIOCGPGRP seems to have that same limitation on
Linux. That's why I quoted the above man page.
Sorry, I missed the point. In view of the use of TIOCGPGRP in emacs,
there must be some unix-like systems (BSD?) where TIOCGPGRP is not
subject to that limitation. Is it necessary to keep the limitation in
Cygwin? I guess it boils down to how important Linux compatibility is,
given that POSIX (as far as I know) is silent about TIOCGPGRP.
This is not a big deal from my point of view. As I said in my first
message, I have a workaround for the most important uses in emacs. I
think it might be more of an issue for mintty.
Ken
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