[Qemu-devel] [RFC 2/3] virtiofsd: add DBus server to handle log level changes

[Stefan Hajnoczi <stefanha@redhat.com>]

Introduce a DBus server thread that runs alongside the other virtiofsd
threads.  It processes changes to the /org/qemu/virtiofsd object which
can be accessed at the org.qemu.virtiofsd location on the bus.

This code does not use locking because we are the only writer to the
int current_log_level variable.  More advanced management commands would
require locking to prevent race conditions with the other threads.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 contrib/virtiofsd/Makefile.objs    |   3 +-
 contrib/virtiofsd/dbus.h           |   9 ++
 contrib/virtiofsd/dbus.c           | 162 +++++++++++++++++++++++++++++
 contrib/virtiofsd/passthrough_ll.c |   8 +-
 4 files changed, 180 insertions(+), 2 deletions(-)
 create mode 100644 contrib/virtiofsd/dbus.h
 create mode 100644 contrib/virtiofsd/dbus.c

diff --git a/contrib/virtiofsd/Makefile.objs b/contrib/virtiofsd/Makefile.objs
index 9b2af1bc23..d59ab60f3d 100644
--- a/contrib/virtiofsd/Makefile.objs
+++ b/contrib/virtiofsd/Makefile.objs
@@ -8,7 +8,8 @@ virtiofsd-obj-y = buffer.o \
                   helper.o \
                   passthrough_ll.o \
                   seccomp.o \
-                  gdbus_generated.o
+                  gdbus_generated.o \
+                  dbus.o
 
 seccomp.o-cflags := $(SECCOMP_CFLAGS)
 seccomp.o-libs := $(SECCOMP_LIBS)
diff --git a/contrib/virtiofsd/dbus.h b/contrib/virtiofsd/dbus.h
new file mode 100644
index 0000000000..aa18e47408
--- /dev/null
+++ b/contrib/virtiofsd/dbus.h
@@ -0,0 +1,9 @@
+#ifndef DBUS_H
+#define DBUS_H
+
+#include <stdbool.h>
+
+bool setup_dbus(void);
+void cleanup_dbus(void);
+
+#endif /* DBUS_H */
diff --git a/contrib/virtiofsd/dbus.c b/contrib/virtiofsd/dbus.c
new file mode 100644
index 0000000000..bc2308e34b
--- /dev/null
+++ b/contrib/virtiofsd/dbus.c
@@ -0,0 +1,162 @@
+#include <assert.h>
+#include <stdio.h>
+#include <glib.h>
+#include "fuse_log.h"
+#include "dbus.h"
+#include "gdbus_generated.h"
+
+static GThread *the_dbus_thread;
+static GMainContext *the_dbus_context;
+static GMainLoop *the_dbus_loop;
+
+/* Set the string property based on the current log level */
+static void refresh_log_level(Virtiofsd *virtiofsd)
+{
+    switch (current_log_level) {
+        case LOG_ERR:
+            virtiofsd_set_log_level(virtiofsd, "err");
+            break;
+        case LOG_WARNING:
+            virtiofsd_set_log_level(virtiofsd, "warning");
+            break;
+        case LOG_INFO:
+            virtiofsd_set_log_level(virtiofsd, "info");
+            break;
+        case LOG_DEBUG:
+            virtiofsd_set_log_level(virtiofsd, "debug");
+            break;
+    }
+}
+
+/* Handle changes to Virtiofsd object properties */
+static void notify(GObject *object, GParamSpec *pspec)
+{
+    Virtiofsd *virtiofsd = VIRTIOFSD(object);
+
+    fprintf(stderr, "%s %s\n", __func__, pspec->name);
+
+    if (strcmp(pspec->name, "log-level") == 0) {
+        const char *s = virtiofsd_get_log_level(virtiofsd);
+
+        if (strcmp(s, "err") == 0) {
+            current_log_level = LOG_ERR;
+        } else if (strcmp(s, "warning") == 0) {
+            current_log_level = LOG_WARNING;
+        } else if (strcmp(s, "info") == 0) {
+            current_log_level = LOG_INFO;
+        } else if (strcmp(s, "debug") == 0) {
+            current_log_level = LOG_DEBUG;
+        } else {
+            /* Invalid, reset the log level property */
+            refresh_log_level(virtiofsd);
+        }
+    }
+}
+
+typedef struct {
+    Virtiofsd *virtiofsd;
+    pthread_barrier_t *started;
+} GBusOwnNameData;
+
+static void bus_acquired(GDBusConnection *connection, const gchar *name,
+        gpointer user_data)
+{
+    GBusOwnNameData *data = user_data;
+    GError *error = NULL;
+
+    if (!g_dbus_interface_skeleton_export(
+                G_DBUS_INTERFACE_SKELETON(data->virtiofsd),
+                connection, "/org/qemu/virtiofsd", &error)) {
+        fuse_err("g_dbus_interface_skeleton_export: %s\n", error->message);
+        g_error_free(error);
+        exit(EXIT_FAILURE);
+    }
+}
+
+static void name_acquired(GDBusConnection *connection, const gchar *name,
+        gpointer user_data)
+{
+    GBusOwnNameData *data = user_data;
+
+    pthread_barrier_wait(data->started);
+}
+
+static void name_lost(GDBusConnection *connection, const gchar *name,
+        gpointer user_data)
+{
+    if (connection) {
+        fuse_err("unable to own dbus name\n");
+    } else {
+        fuse_err("unable to connect to dbus\n");
+    }
+    exit(EXIT_FAILURE);
+}
+
+static gpointer dbus_thread(gpointer opaque)
+{
+    GBusOwnNameData data;
+    Virtiofsd *virtiofsd;
+    guint owner_id;
+
+    g_main_context_push_thread_default(the_dbus_context);
+
+    virtiofsd = virtiofsd_skeleton_new();
+    refresh_log_level(virtiofsd);
+    g_signal_connect(virtiofsd, "notify", G_CALLBACK(notify), NULL);
+
+    data.virtiofsd = virtiofsd;
+    data.started = opaque;
+
+    owner_id = g_bus_own_name(G_BUS_TYPE_SESSION, "org.qemu.virtiofsd",
+            G_BUS_NAME_OWNER_FLAGS_DO_NOT_QUEUE, bus_acquired, name_acquired,
+            name_lost, &data, NULL);
+
+    g_main_loop_run(the_dbus_loop);
+    g_bus_unown_name(owner_id);
+    g_object_unref(virtiofsd);
+
+    g_main_context_pop_thread_default(the_dbus_context);
+    return NULL;
+}
+
+/**
+ * Start DBus server thread.
+ *
+ * Returns: true on success, false on failure
+ */
+bool setup_dbus(void)
+{
+    pthread_barrier_t started;
+
+    assert(!the_dbus_thread);
+
+    fuse_info("Using dbus address %s\n",
+              getenv("DBUS_SESSION_BUS_ADDRESS") ?: "(null)");
+
+    pthread_barrier_init(&started, NULL, 2);
+
+    the_dbus_context = g_main_context_new();
+    the_dbus_loop = g_main_loop_new(the_dbus_context, FALSE);
+    the_dbus_thread = g_thread_new("dbus-thread", dbus_thread, &started);
+
+    pthread_barrier_wait(&started);
+    pthread_barrier_destroy(&started);
+
+    return true;
+}
+
+/**
+ * Stop DBus server thread.
+ */
+void cleanup_dbus(void)
+{
+    g_main_loop_quit(the_dbus_loop);
+    g_thread_join(the_dbus_thread);
+    the_dbus_thread = NULL;
+
+    g_main_loop_unref(the_dbus_loop);
+    the_dbus_loop = NULL;
+
+    g_main_context_unref(the_dbus_context);
+    the_dbus_context = NULL;
+}
diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
index 0ef01b7e3f..0ddd7d280a 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -66,6 +66,7 @@
 #include <gmodule.h>
 #include "fuse_log.h"
 #include "seccomp.h"
+#include "dbus.h"
 
 /* Keep track of inode posix locks for each owner. */
 struct lo_inode_plock {
@@ -2989,6 +2990,9 @@ int main(int argc, char *argv[])
 	if (fuse_session_mount(se) != 0)
 	    goto err_out3;
 
+	if (!setup_dbus())
+	    goto err_out4;
+
 	fuse_daemonize(opts.foreground);
 
 	if (lo.ireg_sock != -1) {
@@ -2998,7 +3002,7 @@ int main(int argc, char *argv[])
 		if (ret) {
 			warnx("pthread_create: %s", strerror(ret));
 			ret = 1;
-			goto err_out4;
+			goto err_out5;
 		}
 
 		get_shared(&lo, &lo.root);
@@ -3014,6 +3018,8 @@ int main(int argc, char *argv[])
 	/* Block until ctrl+c or fusermount -u */
         ret = virtio_loop(se);
 
+err_out5:
+	cleanup_dbus();
 err_out4:
 	fuse_session_unmount(se);
 err_out3:
-- 
2.21.0