bug#73101: Regarding a bug in suspend-emacs

[Riza Dindir <riza.dindir@gmail.com>]

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Hello

Note: Sending this a second time, I forgot to confirm my request to
register to the bug-gnu-emacs list.

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.

Or the information relating to the kernel version and CAP_SYS_ADMIN can be
added to the infor page os suspend_emacs, along with the information on how
to set this capability using sysctl.

Kind Regards
Riza Dindir

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