On Fri, Mar 04 2022, Phillip Wood wrote:
> From: Phillip Wood <phillip.wood@xxxxxxxxxxxxx>
>
> If the user suspends git while it is waiting for a keypress reset the
> terminal before stopping and restore the settings when git resumes. If
> the user tries to resume in the background print an error
> message (taking care to use async safe functions) before stopping
> again. Ideally we would reprint the prompt for the user when git
> resumes but this patch just restarts the read().
>
> The signal handler is established with sigaction() rather than using
> sigchain_push() as this allows us to control the signal mask when the
> handler is invoked and ensure SA_RESTART is used to restart the
> read() when resuming.
>
> Signed-off-by: Phillip Wood <phillip.wood@xxxxxxxxxxxxx>
> ---
> compat/terminal.c | 124 ++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 120 insertions(+), 4 deletions(-)
>
> diff --git a/compat/terminal.c b/compat/terminal.c
> index 5d516ff546..79ab54c2f8 100644
> --- a/compat/terminal.c
> +++ b/compat/terminal.c
> @@ -1,4 +1,4 @@
> -#include "git-compat-util.h"
> +#include "cache.h"
> #include "compat/terminal.h"
> #include "sigchain.h"
> #include "strbuf.h"
> @@ -23,6 +23,89 @@ static void restore_term_on_signal(int sig)
> static int term_fd = -1;
> static struct termios old_term;
>
> +static char *background_resume_msg;
> +static char *restore_error_msg;
> +static volatile sig_atomic_t ttou_received;
> +
> +static void write_msg(const char *msg)
> +{
> + write_in_full(2, msg, strlen(msg));
> + write_in_full(2, "\n", 1);
> +}
> +
> +static void print_background_resume_msg(int signo)
> +{
> + int saved_errno = errno;
> + sigset_t mask;
> + struct sigaction old_sa;
> + struct sigaction sa = { .sa_handler = SIG_DFL };
> +
> + ttou_received = 1;
> + write_msg(background_resume_msg);
> + sigaction(signo, &sa, &old_sa);
> + raise(signo);
> + sigemptyset(&mask);
> + sigaddset(&mask, signo);
> + sigprocmask(SIG_UNBLOCK, &mask, NULL);
> + /* Stopped here */
> + sigprocmask(SIG_BLOCK, &mask, NULL);
> + sigaction(signo, &old_sa, NULL);
> + errno = saved_errno;
> +}
> +
> +static void restore_terminal_on_suspend(int signo)
> +{
> + int saved_errno = errno;
> + int res;
> + struct termios t;
> + sigset_t mask;
> + struct sigaction old_sa;
> + struct sigaction sa = { .sa_handler = SIG_DFL };
> + int can_restore = 1;
> +
> + if (tcgetattr(term_fd, &t) < 0)
> + can_restore = 0;
> +
> + if (tcsetattr(term_fd, TCSAFLUSH, &old_term) < 0)
> + write_msg(restore_error_msg);
> +
> + sigaction(signo, &sa, &old_sa);
> + raise(signo);
> + sigemptyset(&mask);
> + sigaddset(&mask, signo);
> + sigprocmask(SIG_UNBLOCK, &mask, NULL);
> + /* Stopped here */
> + sigprocmask(SIG_BLOCK, &mask, NULL);
> + sigaction(signo, &old_sa, NULL);
> + if (!can_restore) {
> + write_msg(restore_error_msg);
> + goto out;
> + }
> + /*
> + * If we resume in the background then we receive SIGTTOU when calling
> + * tcsetattr() below. Set up a handler to print an error message in that
> + * case.
> + */
> + sigemptyset(&mask);
> + sigaddset(&mask, SIGTTOU);
> + sa.sa_mask = old_sa.sa_mask;
> + sa.sa_handler = print_background_resume_msg;
> + sa.sa_flags = SA_RESTART;
> + sigaction(SIGTTOU, &sa, &old_sa);
> + again:
> + ttou_received = 0;
> + sigprocmask(SIG_UNBLOCK, &mask, NULL);
> + res = tcsetattr(term_fd, TCSAFLUSH, &t);
> + sigprocmask(SIG_BLOCK, &mask, NULL);
> + if (ttou_received)
> + goto again;
> + else if (res < 0)
> + write_msg(restore_error_msg);
> + sigaction(SIGTTOU, &old_sa, NULL);
> + out:
> + errno = saved_errno;
> +}
> +
> void restore_term(void)
> {
> if (term_fd < 0)
> @@ -32,10 +115,19 @@ void restore_term(void)
> close(term_fd);
> term_fd = -1;
> sigchain_pop_common();
> + if (restore_error_msg) {
> + signal(SIGTTIN, SIG_DFL);
> + signal(SIGTTOU, SIG_DFL);
> + signal(SIGTSTP, SIG_DFL);
> + FREE_AND_NULL(restore_error_msg);
> + FREE_AND_NULL(background_resume_msg);
> + }
> }
>
> int save_term(unsigned flags)
> {
> + struct sigaction sa;
> +
> if (term_fd < 0)
> term_fd = (flags & SAVE_TERM_STDIN) ? 0
> : open("/dev/tty", O_RDWR);
> @@ -44,6 +136,26 @@ int save_term(unsigned flags)
> if (tcgetattr(term_fd, &old_term) < 0)
> return -1;
> sigchain_push_common(restore_term_on_signal);
> + /*
> + * If job control is disabled then the shell will have set the
> + * disposition of SIGTSTP to SIG_IGN.
> + */
> + sigaction(SIGTSTP, NULL, &sa);
> + if (sa.sa_handler == SIG_IGN)
> + return 0;
> +
> + /* avoid calling gettext() from signal handler */
> + background_resume_msg = xstrdup(_("error: cannot resume in the background"));
> + restore_error_msg = xstrdup(_("error: cannot restore terminal settings"));
You don't need to xstrdup() the return values of gettext() (here _()),
you'll get a pointer to static storage that's safe to hold on to for the
duration of the program.
In this case I think it would make sense to skip "error: " from the
message itself.
Eventually we'll get to making usage.c have that prefix translated, and
can have some utility function exposed there (I have WIP patches for
this already since a while ago).
To translators it'll look like the same thing, and avoid churn when we
make the "error: " prefix translatable.
Aside: If you do keep the xstrdup() (perhaps an xstrfmt() with the above
advice...) doesn't it make sense to add the "\n" here, so you'll have
one write_in_full() above?
