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cage: switch SIGCHLD handling for pipe

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As explained in [1] and [2], SIGCHLD is a tricky signal to handle. A
pipe can be used to signal completion instead.

[1]: https://github.com/swaywm/wlroots/issues/2012#issuecomment-578908333
[2]: https://stackoverflow.com/questions/8976004/using-waitpid-or-sigaction/8976461#8976461
This commit is contained in:
Jente Hidskes 2020-01-28 21:32:45 +01:00
parent 6be4306b4d
commit 009cca3fa9
1 changed files with 36 additions and 6 deletions
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42
cage.c
View file

@ -49,14 +49,40 @@
#include "xwayland.h"
#endif
static bool
spawn_primary_client(char *argv[], pid_t *pid_out)
static int
sigchld_handler(int fd, uint32_t mask, void *data)
{
struct wl_display *display = data;
/* Close Cage's read pipe. */
close(fd);
if (mask & WL_EVENT_HANGUP) {
wlr_log(WLR_DEBUG, "Child process closed normally");
} else if (mask & WL_EVENT_ERROR) {
wlr_log(WLR_DEBUG, "Connection closed by server");
}
wl_display_terminate(display);
return 0;
}
static bool
spawn_primary_client(struct wl_display *display, char *argv[], pid_t *pid_out, struct wl_event_source **sigchld_source)
{
int fd[2];
if (pipe(fd) != 0) {
wlr_log(WLR_ERROR, "Unable to create pipe");
return false;
}
pid_t pid = fork();
if (pid == 0) {
sigset_t set;
sigemptyset(&set);
sigprocmask(SIG_SETMASK, &set, NULL);
/* Close read, we only need write in the primary client process. */
close(fd[0]);
execvp(argv[0], argv);
_exit(1);
} else if (pid == -1) {
@ -64,6 +90,13 @@ spawn_primary_client(char *argv[], pid_t *pid_out)
return false;
}
/* Close write, we only need read in Cage. */
close(fd[1]);
struct wl_event_loop *event_loop = wl_display_get_event_loop(display);
uint32_t mask = WL_EVENT_HANGUP | WL_EVENT_ERROR;
*sigchld_source = wl_event_loop_add_fd(event_loop, fd[0], mask, sigchld_handler, display);
*pid_out = pid;
wlr_log(WLR_DEBUG, "Child process created with pid %d", pid);
return true;
@ -111,8 +144,6 @@ handle_signal(int signal, void *data)
case SIGINT:
/* Fallthrough */
case SIGTERM:
/* Fallthrough */
case SIGCHLD:
wl_display_terminate(display);
return 0;
default:
@ -230,7 +261,6 @@ main(int argc, char *argv[])
event_loop = wl_display_get_event_loop(server.wl_display);
sigint_source = wl_event_loop_add_signal(event_loop, SIGINT, handle_signal, &server.wl_display);
sigterm_source = wl_event_loop_add_signal(event_loop, SIGTERM, handle_signal, &server.wl_display);
sigchld_source = wl_event_loop_add_signal(event_loop, SIGCHLD, handle_signal, &server.wl_display);
server.backend = wlr_backend_autocreate(server.wl_display, NULL);
if (!server.backend) {
@ -420,7 +450,7 @@ main(int argc, char *argv[])
#endif
pid_t pid;
if (!spawn_primary_client(argv + optind, &pid)) {
if (!spawn_primary_client(server.wl_display, argv + optind, &pid, &sigchld_source)) {
ret = 1;
goto end;
}