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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> 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>

OK, that is less complex than I'd feared.
I guess there's something probably nice to do with name/integer mapping
for warning levels that we could use from one of the libraries.

Dave

> ---
>  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
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK