src: add udev watcher to improve modem recovery

Most of the modem issues follow a (incomplete) USB device reset. Instead 
of relying solely on the existing timer, this patch adds a udev monitor 
which resets the modem as soon as its associated USB device is reset, 
which greatly improves recovery time.

src/manager.c

@@ -9,6 +9,7 @@
 #include "manager.h"
 #include "mm-iface.h"
 #include "suspend.h"
+#include "udev.h"
 
 #include <fcntl.h>
 #include <signal.h>
@@ -30,6 +31,7 @@ static gboolean quit_app(struct EG25Manager *manager)
     at_destroy(manager);
     mm_iface_destroy(manager);
     suspend_destroy(manager);
+    udev_destroy(manager);
 
     if (manager->modem_state >= EG25_STATE_STARTED) {
         g_message("Powering down the modem...");
@@ -202,6 +204,7 @@ int main(int argc, char *argv[])
     gpio_init(&manager);
     mm_iface_init(&manager);
     suspend_init(&manager);
+    udev_init(&manager);
 
     g_idle_add(G_SOURCE_FUNC(modem_start), &manager);
 

src/manager.h

@@ -8,6 +8,7 @@
 
 #include <glib.h>
 #include <gpiod.h>
+#include <gudev/gudev.h>
 #include <libmm-glib.h>
 
 enum EG25State {
@@ -44,6 +45,7 @@ struct EG25Manager {
     int suspend_inhibit_fd;
     guint suspend_source;
 
+    GUdevClient *udev;
 
     struct gpiod_chip *gpiochip[2];
     struct gpiod_line *gpio_out[5];

src/meson.build

@@ -12,6 +12,7 @@ executable (
         'manager.c', 'manager.h',
         'mm-iface.c', 'mm-iface.h',
         'suspend.c', 'suspend.h',
+        'udev.c', 'udev.h',
     ],
     dependencies : mgr_deps,
     install : true

src/suspend.c

@@ -158,6 +158,10 @@ void suspend_init(struct EG25Manager *manager)
 void suspend_destroy(struct EG25Manager *manager)
 {
     drop_inhibitor(manager);
+    if (manager->suspend_source) {
+        g_source_remove(manager->suspend_source);
+        manager->suspend_source = 0;
+    }
     if (manager->suspend_proxy) {
         g_object_unref(manager->suspend_proxy);
         manager->suspend_proxy = NULL;

src/udev.c

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2020 Arnaud Ferraris <arnaud.ferraris@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include "udev.h"
+
+#include <string.h>
+
+static void udev_event_cb(GUdevClient *client, gchar *action, GUdevDevice *device, gpointer data)
+{
+    struct EG25Manager *manager = data;
+
+    if (strcmp(action, "unbind") != 0 || manager->modem_state == EG25_STATE_RESETTING)
+        return;
+
+    if (strncmp(g_udev_device_get_name(device), manager->modem_usb_id, strlen(manager->modem_usb_id)) == 0 &&
+        manager->reset_timer == 0) {
+        g_message("Lost modem, resetting...");
+        modem_reset(manager);
+    }
+}
+
+void udev_init (struct EG25Manager *manager)
+{
+    const char * const subsystems[] = { "usb", NULL };
+
+    manager->udev = g_udev_client_new(subsystems);
+    g_signal_connect(manager->udev, "uevent", G_CALLBACK(udev_event_cb), manager);
+
+    return;
+}
+
+void udev_destroy (struct EG25Manager *manager)
+{
+    if (manager->udev) {
+        g_object_unref(manager->udev);
+        manager->udev = NULL;
+    }
+}

src/udev.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright (C) 2020 Arnaud Ferraris <arnaud.ferraris@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include "manager.h"
+
+void udev_init (struct EG25Manager *data);
+void udev_destroy (struct EG25Manager *data);