[virt-viewer PATCH v2] remote-viewer: add handler for SIGINT signal

[Francesco Giudici]

When remote-viewer is started from terminal, CTRL-C sends a SIGINT
signal to the program causing immediate termination. On linux clients
usb redirected devices are left without any kernel driver attached,
causing them to appear as no more available to the host.
Add a SIGINT handler to allow a clean exit, in particular to allow
the kernel to attach back the host driver.
The issue is present on linux only.

To perform usb device redirection, virt-viewer leverages spice-gtk
library, which in turn relies on usbredir library, which uses libusb.
In order to take control of the usb device the auto-loaded kernel
driver must be detached. This is achieved (in the very end) with
libusb_detach_kernel_driver(). Then the device interfaces can be claimed
with libusb_claim_interface() and get in control to the application.
During normal application termination, the usb channel is teared down,
performing a reset of the usb device and giving back the control of the
device to the kernel (libusb_attach_kernel_driver()).
If the application quits without doing this, the device interfaces will
end up with no driver attached, making them not usable in the host
system.

Note that enabling libusb_set_auto_detach_kernel_driver() does not solve
the issue, as this is just a convenient API from libusb: libusb will
take care of detaching/attaching the driver to the interfaces of the usb
device each time a call to libusb_release_interface() and
libusb_claim_interface() is performed. An unexpected quit of the
application will skip the libusb_release_interface() call too, leaving
the interfaces without any driver attached.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1713311

Signed-off-by: Francesco Giudici <fgiudici at redhat.com>
---
 src/virt-viewer-app.c | 79 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/src/virt-viewer-app.c b/src/virt-viewer-app.c
index da8cfa9..06e237b 100644
--- a/src/virt-viewer-app.c
+++ b/src/virt-viewer-app.c
@@ -36,6 +36,7 @@
 #include <glib/gprintf.h>
 #include <glib/gi18n.h>
 #include <errno.h>
+#include <fcntl.h>
 
 #ifdef HAVE_SYS_SOCKET_H
 #include <sys/socket.h>
@@ -1756,6 +1757,74 @@ static gboolean opt_fullscreen = FALSE;
 static gboolean opt_kiosk = FALSE;
 static gboolean opt_kiosk_quit = FALSE;
 
+#ifndef G_OS_WIN32
+static int sigint_pipe[2];
+
+static void
+sigint_handler(int signum)
+{
+    int savedErrno;
+
+    g_return_if_fail(signum == SIGINT);
+
+    savedErrno = errno;
+    if (write(sigint_pipe[1], "x", 1) == -1 && errno != EAGAIN)
+        g_debug("SIGINT handler failure\n");
+    errno = savedErrno;
+}
+
+static void
+register_sigint_handler()
+{
+    int flags, i;
+    struct sigaction sa;
+
+    if (pipe(sigint_pipe) == -1)
+        goto err;
+
+    for (i = 0; i < 2; i++) {
+        flags = fcntl(sigint_pipe[i], F_GETFL);
+        if (flags == -1)
+            goto err;
+        flags |= O_NONBLOCK;
+        if (fcntl(sigint_pipe[i], F_SETFL, flags) == -1)
+            goto err;
+    }
+
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_RESTART;
+    sa.sa_handler = sigint_handler;
+    if (sigaction(SIGINT, &sa, NULL) == -1)
+        goto err;
+
+    return;
+
+err:
+    g_debug("Cannot register SIGINT handler\n");
+}
+
+static gboolean
+sigint_cb(GIOChannel *source,
+          GIOCondition condition,
+          gpointer data)
+{
+    VirtViewerApp *self = VIRT_VIEWER_APP(data);
+    VirtViewerAppPrivate *priv = self->priv;
+    gchar sbuf;
+
+    g_assert(condition == G_IO_IN);
+
+    g_debug("got SIGINT, quitting\n");
+    if (priv->started)
+        virt_viewer_app_quit(self);
+    else
+        exit(0);
+
+    g_io_channel_read_chars (source, &sbuf, 1, NULL, NULL);
+    return TRUE;
+}
+#endif
+
 static void
 title_maybe_changed(VirtViewerApp *self, GParamSpec* pspec G_GNUC_UNUSED, gpointer user_data G_GNUC_UNUSED)
 {
@@ -1766,10 +1835,20 @@ static void
 virt_viewer_app_init(VirtViewerApp *self)
 {
     GError *error = NULL;
+#ifndef G_OS_WIN32
+    GIOChannel *sigint_channel = NULL;
+#endif
+
     self->priv = virt_viewer_app_get_instance_private(self);
 
     gtk_window_set_default_icon_name("virt-viewer");
 
+#ifndef G_OS_WIN32
+    register_sigint_handler();
+    sigint_channel = g_io_channel_unix_new(sigint_pipe[0]);
+    g_io_add_watch(sigint_channel, G_IO_IN, sigint_cb, self);
+#endif
+
     self->priv->displays = g_hash_table_new_full(g_direct_hash, g_direct_equal, NULL, g_object_unref);
     self->priv->config = g_key_file_new();
     self->priv->config_file = g_build_filename(g_get_user_config_dir(),
-- 
2.21.1