Hello Eli, I am new to the code base, and it was just a suggestion to check for the ioctl call for any failures and take precautions, maybe inform the user of the issue that the suspend-emacs command did not run correctly. Since the command was not printing out anything when called with 'M-: (suspend-emacs "pwd")' I was not sure what was happening.
For users that use the linux kernel 6.2+ the ioctl command does not work correctly. When the STUFFSTRING is passed to the suspend-emacs command, it does nothing. The problem with kernel 6.2+ is that it requires CAP_SYS_ADMIN capability (https://www.man7.org/linux/man-pages/man2/TIOCSTI.2const.html). In the code at some point suspend-emacs command calls stuff_char, which uses ioctl (code snippet below, from https://git.savannah.gnu.org/cgit/emacs.git/tree/src/sysdep.c#n403). The ioctl call fails. But in the code there is no check for that, that might confuse people that use linux kernel 6.2+. I wanted to use suspend-emacs with "pwd" as the string (as shown in the example in the documentation in https://www.gnu.org/software/emacs/manual/html_node/elisp/Suspending-Emacs.html). But the "pwd" command was not displaying anything. Because it was not being sent/stuffed to the superior process. /* Should perhaps error if in batch mode */#ifdef TIOCSTI ioctl (fileno (CURTTY()->input), TIOCSTI, &c);#else /* no TIOCSTI */ error ("Cannot stuff terminal input characters in this version of Unix");#endif /* no TIOCSTI */ I have downloaded the code for emacs 29.4 and compiled it with a simple error check and the ioctl call failed on my system silently (with kernel 6.6.47). To add a check is of course for the people who develop emacs to decide. I have seen the code today, and am not in a position to suggest anything at this stage. Maybe there would be a better way of handling this error. Adding an error check would be one of the solutions. The other solution might be to add a piece of information to the documentation for suspend-emacs, (and maybe to the documentation string for suspend-emacs) regarding this problem. So that people that use linux kernel 6.2+ would be aware of this issue. The issue is fixable by just setting the dev.tty.legacy_tiocsti sysctl variable to 1. This variable was set to 0 on my system. Hence the ioctl call for TIOCSTI was failing, and no indication of the error was given. After I have read the man page for TIOCSTI, and set the sysctl variable dev.tty.legacy_tiocsti to 1 was I able to call suspend-emacs with a STUFFSTRING and it worked. It was displaying the output of the "pwd" command. Regards Riza On Sat, Sep 7, 2024, 18:20 Eli Zaretskii <e...@gnu.org> wrote: > > From: Riza Dindir <riza.din...@gmail.com> > > Date: Sat, 7 Sep 2024 15:37:17 +0300 > > > > I am running Linux with kernel 6.6.47 and am running emacs in xterm, > using the -nw command line argument. > > > > I am new to emacs and was experimenting with the suspend-emacs command. > Following the example on > > > https://www.gnu.org/software/emacs/manual/html_node/elisp/Suspending-Emacs.html > . > > > > When following the example, I added the suspend-resume-hook to my > .emacs.d/init.el file. When I run M-: > > (suspend-emacs "pwd") it does not show the current working directory. > But when I do fg from the terminal that I > > got into, I see the "Resumed!" message. > > > > I asked in the libera chat about that, and also in the gnu-help-emacs > list. I have been talking to wasamasa on > > libera chat (#emacs-beginners) and we pinpointed the problem to the > stuff_char function (in > > https://git.savannah.gnu.org/cgit/emacs.git/tree/src/sysdep.c#n403). We > came to this point from > > stuff_buffered_input ( > https://git.savannah.gnu.org/cgit/emacs.git/tree/src/keyboard.c#n11963), > and from > > suspend-emacs function definition (in > https://git.savannah.gnu.org/cgit/emacs.git/tree/src/keyboard.c#n11908). > > > > The stuff_char function is using ioctl with TIOCSTI. TIOCSTI requires > CAP_SYS_ADMIN capability. You can set > > this capability using sysctl setting dev.tty.legacy_tiocsti to 1. > > > > Unless I had set "dev.tty.legacy_tiocsti" to 1 I could not run the > suspend-emacs command with an argument > > string. > > > > Either emacs can check the return value of ioctl in stuff_char and if > there return value is EPERM, then handle > > this accordingly, with a message regarding the problem. > > You mean, you want suspend-emacs signal an error if it is called with > STUFFSTRING argument, but fails to stuff the string into the > terminal's input buffer? >
