Disconnect swaybg instead of killing it

This is much more reliable. This also fixes race conditions when killing swaybg
while it's doing a wl_display_roundtrip.

4 files changed, 80 insertions, 26 deletions

diff --git a/include/sway/output.h b/include/sway/output.h
index 479897ef..ea7a2174 100644
--- a/include/sway/output.h
+++ b/include/sway/output.h
@@ -21,6 +21,7 @@ struct sway_output {
         struct sway_node node;
         struct wlr_output *wlr_output;
         struct sway_server *server;
+        struct wl_list link;
 
         struct wl_list layers[4]; // sway_layer_surface::link
         struct wlr_box usable_area;
@@ -36,6 +37,8 @@ struct sway_output {
 
         struct sway_output_state current;
 
+        struct wl_client *swaybg_client;
+
         struct wl_listener destroy;
         struct wl_listener mode;
         struct wl_listener transform;
@@ -43,10 +46,7 @@ struct sway_output {
         struct wl_listener present;
         struct wl_listener damage_destroy;
         struct wl_listener damage_frame;
-
-        struct wl_list link;
-
-        pid_t bg_pid;
+        struct wl_listener swaybg_client_destroy;
 
         struct {
                 struct wl_signal destroy;
diff --git a/sway/config/output.c b/sway/config/output.c
index 0f238715..513d03e0 100644
--- a/sway/config/output.c
+++ b/sway/config/output.c
@@ -1,16 +1,17 @@
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
+#include <fcntl.h>
 #include <stdbool.h>
 #include <string.h>
-#include <signal.h>
+#include <sys/socket.h>
 #include <sys/wait.h>
 #include <unistd.h>
-#include <wlr/types/wlr_output.h>
 #include <wlr/types/wlr_output_layout.h>
+#include <wlr/types/wlr_output.h>
+#include "log.h"
 #include "sway/config.h"
 #include "sway/output.h"
 #include "sway/tree/root.h"
-#include "log.h"
 
 int output_name_cmp(const void *item, const void *data) {
         const struct output_config *output = item;
@@ -165,14 +166,71 @@ static bool set_mode(struct wlr_output *output, int width, int height,
         return wlr_output_set_mode(output, best);
 }
 
-void terminate_swaybg(pid_t pid) {
-        int ret = kill(pid, SIGTERM);
-        if (ret != 0) {
-                sway_log(SWAY_ERROR, "Unable to terminate swaybg [pid: %d]", pid);
-        } else {
-                int status;
-                waitpid(pid, &status, 0);
+static void handle_swaybg_client_destroy(struct wl_listener *listener,
+                void *data) {
+        struct sway_output *output =
+                wl_container_of(listener, output, swaybg_client_destroy);
+        wl_list_remove(&output->swaybg_client_destroy.link);
+        wl_list_init(&output->swaybg_client_destroy.link);
+        output->swaybg_client = NULL;
+}
+
+static bool spawn_swaybg(struct sway_output *output, char *const cmd[]) {
+        int sockets[2];
+        if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, sockets) != 0) {
+                sway_log_errno(SWAY_ERROR, "socketpair failed");
+                return false;
+        }
+
+        output->swaybg_client = wl_client_create(server.wl_display, sockets[0]);
+        if (output->swaybg_client == NULL) {
+                sway_log_errno(SWAY_ERROR, "wl_client_create failed");
+                return false;
+        }
+
+        output->swaybg_client_destroy.notify = handle_swaybg_client_destroy;
+        wl_client_add_destroy_listener(output->swaybg_client,
+                &output->swaybg_client_destroy);
+
+        pid_t pid = fork();
+        if (pid < 0) {
+                sway_log_errno(SWAY_ERROR, "fork failed");
+                return false;
+        } else if (pid == 0) {
+                pid = fork();
+                if (pid < 0) {
+                        sway_log_errno(SWAY_ERROR, "fork failed");
+                        exit(EXIT_FAILURE);
+                } else if (pid == 0) {
+                        // Remove the CLOEXEC flag
+                        int flags = fcntl(sockets[1], F_GETFD);
+                        if (flags == -1) {
+                                sway_log_errno(SWAY_ERROR, "fcntl() failed");
+                                exit(EXIT_FAILURE);
+                        }
+                        if (fcntl(sockets[1], F_SETFD, flags & ~FD_CLOEXEC) == -1) {
+                                sway_log_errno(SWAY_ERROR, "fcntl() failed");
+                                exit(EXIT_FAILURE);
+                        }
+
+                        char wayland_socket_str[16];
+                        snprintf(wayland_socket_str, sizeof(wayland_socket_str),
+                                "%d", sockets[1]);
+                        setenv("WAYLAND_SOCKET", wayland_socket_str, true);
+
+                        execvp(cmd[0], cmd);
+                        sway_log_errno(SWAY_ERROR, "execvp failed");
+                        exit(EXIT_FAILURE);
+                }
+                exit(EXIT_SUCCESS);
         }
+
+        if (waitpid(pid, NULL, 0) < 0) {
+                sway_log_errno(SWAY_ERROR, "waitpid failed");
+                return false;
+        }
+
+        return true;
 }
 
 bool apply_output_config(struct output_config *oc, struct sway_output *output) {
@@ -243,8 +301,8 @@ bool apply_output_config(struct output_config *oc, struct sway_output *output) {
                 wlr_output_layout_add_auto(root->output_layout, wlr_output);
         }
 
-        if (output->bg_pid != 0) {
-                terminate_swaybg(output->bg_pid);
+        if (output->swaybg_client != NULL) {
+                wl_client_destroy(output->swaybg_client);
         }
         if (oc && oc->background && config->swaybg_command) {
                 sway_log(SWAY_DEBUG, "Setting background for output %s to %s",
@@ -258,13 +316,8 @@ bool apply_output_config(struct output_config *oc, struct sway_output *output) {
                         oc->background_fallback ? oc->background_fallback : NULL,
                         NULL,
                 };
-
-                output->bg_pid = fork();
-                if (output->bg_pid < 0) {
-                        sway_log_errno(SWAY_ERROR, "fork failed");
-                } else if (output->bg_pid == 0) {
-                        execvp(cmd[0], cmd);
-                        sway_log_errno(SWAY_ERROR, "Failed to execute swaybg");
+                if (!spawn_swaybg(output, cmd)) {
+                        return false;
                 }
         }
 
diff --git a/sway/desktop/output.c b/sway/desktop/output.c
index ad75bb35..c5461ee6 100644
--- a/sway/desktop/output.c
+++ b/sway/desktop/output.c
@@ -506,6 +506,7 @@ static void handle_destroy(struct wl_listener *listener, void *data) {
         wl_list_remove(&output->present.link);
         wl_list_remove(&output->damage_destroy.link);
         wl_list_remove(&output->damage_frame.link);
+        wl_list_remove(&output->swaybg_client_destroy.link);
 
         transaction_commit_dirty();
 }
@@ -612,6 +613,7 @@ void handle_new_output(struct wl_listener *listener, void *data) {
         output->damage_frame.notify = damage_handle_frame;
         wl_signal_add(&output->damage->events.destroy, &output->damage_destroy);
         output->damage_destroy.notify = damage_handle_destroy;
+        wl_list_init(&output->swaybg_client_destroy.link);
 
         struct output_config *oc = output_find_config(output);
         if (!oc || oc->enabled) {
diff --git a/sway/tree/output.c b/sway/tree/output.c
index 138144a7..60e0af9f 100644
--- a/sway/tree/output.c
+++ b/sway/tree/output.c
@@ -233,9 +233,8 @@ void output_disable(struct sway_output *output) {
 
         root_for_each_container(untrack_output, output);
 
-        if (output->bg_pid) {
-                terminate_swaybg(output->bg_pid);
-                output->bg_pid = 0;
+        if (output->swaybg_client != NULL) {
+                wl_client_destroy(output->swaybg_client);
         }
 
         int index = list_find(root->outputs, output);