Merge lp:~rhansen/lightdm/multiseat-logging into lp:lightdm

[Richard Hansen]

Extend logging to make it easier to troubleshoot multiseat setups:
  * include seat name in Seat log messages
  * include display server name in DisplayServer log messages
  * include PID in Session log messages
  * log the values of the XDG_SEAT and XDG_VTNR PAM variables

[Robert Ancell (robert-ancell)]

Nice work!

There seems to be no default value set for seats, i.e. if you do:
$ cd tests
$ DEBUG=1 ./test-autologin

you get logs like:

[+0.00s] DEBUG: Seat (null): Creating user session

If the ID is NULL, id expect to see:

[+0.00s] DEBUG: Seat: Creating user session

or at least a valid ID.

You don't need to break at 80 characters, I've fixed the whitespace in this branch:
lp:~robert-ancell/lightdm/multiseat-logging-whitespace
(I suggest you manually patch to keep the attribution to you for the changes).

Also, now the logging is better, we have some redundant text.

[+0.00s] DEBUG: Seat (null): Starting seat

should become

[+0.00s] DEBUG: Seat (null): Starting

Though I wont block this merge on this. We can fix this in a later MP if you like.

review: Needs Fixing

[Richard Hansen (rhansen)]

> There seems to be no default value set for seats, i.e. if you do:
> $ cd tests
> $ DEBUG=1 ./test-autologin
>
> you get logs like:
>
> [+0.00s] DEBUG: Seat (null): Creating user session
>
> If the ID is NULL, id expect to see:
>
> [+0.00s] DEBUG: Seat: Creating user session
>
> or at least a valid ID.

OK, I'll see what I can do to improve it.

>
> You don't need to break at 80 characters

I really dislike lines longer than 80 characters, which is why I
usually wrap long lines when I change them. I'll unwrap, but I'll
feel like I'm violating my own principles. :)

See [1] for why don't I like lines longer than 80 characters.

[1] http://stackoverflow.com/a/111009/712605

>
> Also, now the logging is better, we have some redundant text.
>
> [+0.00s] DEBUG: Seat (null): Starting seat
>
> should become
>
> [+0.00s] DEBUG: Seat (null): Starting
>
> Though I wont block this merge on this. We can fix this in a later
> MP if you like.

I caught some of those (e.g., "starting session with PID=xxx"), but it
looks like I missed some. I'll do an audit.

Unmerged revisions

1762. By Richard Hansen on 2013-08-04

log the values of the XDG_SEAT and XDG_VTNR variables

This makes it easier to debug multiseat setups.

1761. By Richard Hansen on 2013-08-04

delay setting Session pid to 0 (for logging)

The Session pid is currently used in Session log messages. Delay
setting it to 0 so that more log messages have a meaningful prefix (to
make it possible to correlate them with other log messages).

1760. By Richard Hansen on 2013-08-04

add session PID to Session (including Greeter) log messages

This makes it easier to debug multiseat setups.

1759. By Richard Hansen on 2013-08-04

have Session implement the Logger interface

This is a step toward logging the session PID in each Session
log message, which will make it easier to debug multiseat setups.

The PID is set to 0 when the Session process terminates, so it is not
possible to follow a Session's complete lifetime in the logs. But
it's better than nothing.

A future commit could easily change this to log some other identifier,
such as the associated Display or Seat name, or the PID before the
process terminated.

1758. By Richard Hansen on 2013-08-04

add display server name to DisplayServer log messages

This makes it easier to debug multiseat setups.

1757. By Richard Hansen on 2013-08-04

have DisplayServer implement the Logger interface

This is a step toward logging the display server name in each
DisplayServer log message, which will make it easier to debug
multiseat setups.

1756. By Richard Hansen on 2013-08-04

add seat name to Seat log messages

This makes it easier to debug multiseat setups.

1755. By Richard Hansen on 2013-08-04

have Seat implement the Logger interface

This is a step toward logging the seat name in each Seat log message,
which will make it easier to debug multiseat setups.

1754. By Richard Hansen on 2013-08-04

make the Seat available everywhere a log message is generated

This will make it possible to prefix the log messages with the Seat's
name.

1753. By Richard Hansen on 2013-08-04

save the Seat name when parsing the config file

This will be used to prefix each Seat log message with the seat name.

=== modified file 'src/Makefile.am'
--- src/Makefile.am	2013-07-24 23:53:37 +0000
+++ src/Makefile.am	2013-08-05 07:39:31 +0000
@@ -18,6 +18,8 @@
 	guest-account.c \
 	guest-account.h \
 	lightdm.c \
+	logger.c \
+	logger.h \
 	login1.c \
 	login1.h \
 	mir-server.c \

=== modified file 'src/display-server.c'
--- src/display-server.c	2013-07-26 04:50:35 +0000
+++ src/display-server.c	2013-08-05 07:39:31 +0000
@@ -32,7 +32,11 @@
     gboolean stopped;
 };
 
-G_DEFINE_TYPE (DisplayServer, display_server, G_TYPE_OBJECT);
+static void display_server_logger_iface_init (LoggerInterface *iface);
+
+G_DEFINE_TYPE_WITH_CODE (DisplayServer, display_server, G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (
+                             LOGGER_TYPE, display_server_logger_iface_init));
 
 void
 display_server_set_name (DisplayServer *server, const gchar *name)
@@ -176,3 +180,17 @@
                       NULL,
                       G_TYPE_NONE, 0);
 }
+
+static gint
+display_server_real_logprefix (Logger *self, gchar *buf, gulong buflen)
+{
+    DisplayServer *server = DISPLAY_SERVER (self);
+    return g_snprintf (buf, buflen, "DisplayServer %s: ",
+                       display_server_get_name (server));
+}
+
+static void
+display_server_logger_iface_init (LoggerInterface *iface)
+{
+    iface->logprefix = &display_server_real_logprefix;
+}

=== modified file 'src/display-server.h'
--- src/display-server.h	2013-07-26 02:54:55 +0000
+++ src/display-server.h	2013-08-05 07:39:31 +0000
@@ -16,6 +16,7 @@
 
 typedef struct DisplayServer DisplayServer;
 
+#include "logger.h"
 #include "session.h"
 
 G_BEGIN_DECLS

=== modified file 'src/greeter.c'
--- src/greeter.c	2013-07-24 23:53:37 +0000
+++ src/greeter.c	2013-08-05 07:39:31 +0000
@@ -164,7 +164,7 @@
 
     g_io_channel_write_chars (greeter->priv->to_greeter_channel, (gchar *) message, message_length, NULL, &error);
     if (error)
-        g_warning ("Error writing to greeter: %s", error->message);
+        l_warning (greeter, "Error writing to greeter: %s", error->message);
     g_clear_error (&error);
     g_io_channel_flush (greeter->priv->to_greeter_channel, NULL);
 }
@@ -225,7 +225,7 @@
     GHashTableIter iter;
     gpointer key, value;
 
-    g_debug ("Greeter connected version=%s", version);
+    l_debug (greeter, "Greeter connected version=%s", version);
 
     length = string_length (VERSION);
     g_hash_table_iter_init (&iter, greeter->priv->hints);
@@ -260,7 +260,7 @@
     messages_length = session_get_messages_length (session);
 
     /* Respond to d-bus query with messages */
-    g_debug ("Prompt greeter with %d message(s)", messages_length);
+    l_debug (greeter, "Prompt greeter with %d message(s)", messages_length);
     size = int_length () + string_length (session_get_username (session)) + int_length ();
     for (i = 0; i < messages_length; i++)
         size += int_length () + string_length (messages[i].msg);
@@ -308,16 +308,21 @@
 {
     int result;
 
-    g_debug ("Authenticate result for user %s: %s", session_get_username (session), session_get_authentication_result_string (session));
+    l_debug (greeter,
+        "Authenticate result for user %s: %s", session_get_username (session),
+        session_get_authentication_result_string (session));
 
     result = session_get_authentication_result (session);
     if (session_get_is_authenticated (session))
     {
         if (session_get_user (session))
-            g_debug ("User %s authorized", session_get_username (session));
+            l_debug (greeter,
+                "User %s authorized", session_get_username (session));
         else
         {
-            g_debug ("User %s authorized, but no account of that name exists", session_get_username (session));          
+            l_debug (greeter,
+                "User %s authorized, but no account of that name exists",
+                session_get_username (session));
             result = PAM_USER_UNKNOWN;
         }
     }
@@ -349,11 +354,11 @@
 
     if (username[0] == '\0')
     {
-        g_debug ("Greeter start authentication");
+        l_debug (greeter, "Greeter start authentication");
         username = NULL;
     }
     else
-        g_debug ("Greeter start authentication for %s", username);
+        l_debug (greeter, "Greeter start authentication for %s", username);
 
     reset_session (greeter);
 
@@ -392,13 +397,13 @@
 static void
 handle_login_as_guest (Greeter *greeter, guint32 sequence_number)
 {
-    g_debug ("Greeter start authentication for guest account");
+    l_debug (greeter, "Greeter start authentication for guest account");
 
     reset_session (greeter);
 
     if (!greeter->priv->allow_guest)
     {
-        g_debug ("Guest account is disabled");
+        l_debug (greeter, "Guest account is disabled");
         send_end_authentication (greeter, sequence_number, "", PAM_USER_UNKNOWN);
         return;
     }
@@ -449,11 +454,14 @@
 
     if (username[0] == '\0')
     {
-        g_debug ("Greeter start authentication for remote session %s", session_name);
+        l_debug (greeter,
+            "Greeter start authentication for remote session %s", session_name);
         username = NULL;
     }
     else
-        g_debug ("Greeter start authentication for remote session %s as user %s", session_name, username);
+        l_debug (greeter,
+            "Greeter start authentication for remote session %s as user %s",
+            session_name, username);
 
     reset_session (greeter);
 
@@ -518,7 +526,7 @@
         return;
     }
 
-    g_debug ("Continue authentication");
+    l_debug (greeter, "Continue authentication");
 
     /* Build response */
     response = calloc (messages_length, sizeof (struct pam_response));
@@ -548,7 +556,7 @@
     if (greeter->priv->authentication_session == NULL)
         return;
 
-    g_debug ("Cancel authentication");
+    l_debug (greeter, "Cancel authentication");
     reset_session (greeter);
 }
 
@@ -573,15 +581,16 @@
     if (greeter->priv->guest_account_authenticated || session_get_is_authenticated (greeter->priv->authentication_session))
     {
         if (session)
-            g_debug ("Greeter requests session %s", session);
+            l_debug (greeter, "Greeter requests session %s", session);
         else
-            g_debug ("Greeter requests default session");
+            l_debug (greeter, "Greeter requests default session");
         greeter->priv->start_session = TRUE;
         g_signal_emit (greeter, signals[START_SESSION], 0, session_type, session, &result);
     }
     else
     {
-        g_debug ("Ignoring start session request, user is not authorized");
+        l_debug (greeter,
+            "Ignoring start session request, user is not authorized");
         result = FALSE;
     }
 
@@ -597,18 +606,19 @@
 
     if (!greeter->priv->guest_account_authenticated && !session_get_is_authenticated (greeter->priv->authentication_session))
     {
-        g_debug ("Ignoring set language request, user is not authorized");
+        l_debug (greeter,
+            "Ignoring set language request, user is not authorized");
         return;
     }
 
     // FIXME: Could use this
     if (greeter->priv->guest_account_authenticated)
     {
-        g_debug ("Ignoring set language request for guest user");
+        l_debug (greeter, "Ignoring set language request for guest user");
         return;
     }
 
-    g_debug ("Greeter sets language %s", language);
+    l_debug (greeter, "Greeter sets language %s", language);
     user = session_get_user (greeter->priv->authentication_session);
     user_set_language (user, language);
 }
@@ -620,7 +630,9 @@
     guint8 *buffer;
     if (greeter->priv->n_read - *offset < sizeof (guint32))
     {
-        g_warning ("Not enough space for int, need %zu, got %zu", sizeof (guint32), greeter->priv->n_read - *offset);
+        l_warning (greeter,
+            "Not enough space for int, need %zu, got %zu",
+            sizeof (guint32), greeter->priv->n_read - *offset);
         return 0;
     }
     buffer = greeter->priv->read_buffer + *offset;
@@ -640,7 +652,8 @@
 
     if (HEADER_SIZE + payload_length < HEADER_SIZE)
     {
-        g_warning ("Payload length of %u octets too long", payload_length);
+        l_warning (greeter,
+            "Payload length of %u octets too long", payload_length);
         return HEADER_SIZE;
     }
 
@@ -656,7 +669,9 @@
     length = read_int (greeter, offset);
     if (greeter->priv->n_read - *offset < length)
     {
-        g_warning ("Not enough space for string, need %u, got %zu", length, greeter->priv->n_read - *offset);
+        l_warning (greeter,
+            "Not enough space for string, need %u, got %zu",
+            length, greeter->priv->n_read - *offset);
         return g_strdup ("");
     }
 
@@ -697,7 +712,7 @@
 
     if (condition == G_IO_HUP)
     {
-        g_debug ("Greeter closed communication channel");
+        l_debug (greeter, "Greeter closed communication channel");
         return FALSE;
     }
   
@@ -715,7 +730,7 @@
                                       &n_read,
                                       &error);
     if (error)
-        g_warning ("Error reading from greeter: %s", error->message);
+        l_warning (greeter, "Error reading from greeter: %s", error->message);
     g_clear_error (&error);
     if (status != G_IO_STATUS_NORMAL)
         return TRUE;
@@ -767,7 +782,8 @@
         max_secrets = (G_MAXUINT32 - 1) / sizeof (gchar *);
         if (n_secrets > max_secrets)
         {
-            g_warning ("Array length of %u elements too long", n_secrets);
+            l_warning (greeter,
+                "Array length of %u elements too long", n_secrets);
             return FALSE;
         }
         secrets = g_malloc (sizeof (gchar *) * (n_secrets + 1));
@@ -793,7 +809,7 @@
         g_free (language);
         break;
     default:
-        g_warning ("Unknown message from greeter: %d", id);
+        l_warning (greeter, "Unknown message from greeter: %d", id);
         break;
     }
 

=== modified file 'src/lightdm.c'
--- src/lightdm.c	2013-07-24 03:02:30 +0000
+++ src/lightdm.c	2013-08-05 07:39:31 +0000
@@ -1168,8 +1168,9 @@
         gchar *config_section = *i;
         gchar *type;
         Seat *seat;
+        const gchar *const seatpfx = "Seat:";
 
-        if (!g_str_has_prefix (config_section, "Seat:"))
+        if (!g_str_has_prefix (config_section, seatpfx))
             continue;
 
         g_debug ("Loading seat %s", config_section);
@@ -1180,6 +1181,11 @@
         g_free (type);
         if (seat)
         {
+            const gsize seatpfxlen = strlen(seatpfx);
+            gchar *seatname = config_section + seatpfxlen;
+
+            seat_set_property (seat, "seat-name", seatname);
+
             set_seat_properties (seat, config_section);
             display_manager_add_seat (display_manager, seat);
             g_object_unref (seat);

=== added file 'src/logger.c'
--- src/logger.c	1970-01-01 00:00:00 +0000
+++ src/logger.c	2013-08-05 07:39:31 +0000
@@ -0,0 +1,85 @@
+#include "logger.h"
+
+G_DEFINE_INTERFACE (Logger, logger, G_TYPE_INVALID);
+
+static void
+logger_logv_default (Logger *self, GLogLevelFlags log_level,
+                     const gchar *format, va_list ap);
+
+static void
+logger_default_init (LoggerInterface *iface)
+{
+    iface->logv = &logger_logv_default;
+}
+
+gint
+logger_logprefix (Logger *self, gchar *buf, gulong buflen)
+{
+    g_return_val_if_fail (IS_LOGGER (self), -1);
+    return LOGGER_GET_INTERFACE (self)->logprefix (self, buf, buflen);
+}
+
+void
+logger_logv (Logger *self, GLogLevelFlags log_level,
+             const gchar *format, va_list ap)
+{
+    g_return_if_fail (IS_LOGGER (self));
+    LOGGER_GET_INTERFACE (self)->logv (self, log_level, format, ap);
+}
+
+void
+logger_logv_default (Logger *self, GLogLevelFlags log_level,
+                     const gchar *format, va_list ap)
+{
+    va_list ap_copy;
+    gint tmp;
+
+    /* figure out how long the prefix is */
+    tmp = logger_logprefix (self, NULL, 0);
+    if (tmp < 0)
+    {
+        g_error ("failed to get log prefix");
+        return;
+    }
+
+    /* print the prefix to a variable length array (to avoid malloc) */
+    gchar pfx[tmp + 1];
+    tmp = logger_logprefix (self, pfx, sizeof(pfx));
+    if (tmp < 0)
+    {
+        g_error ("failed to get log prefix");
+        return;
+    }
+
+    /* figure out how long the formatted message is */
+    va_copy (ap_copy, ap);
+    tmp = g_vsnprintf (NULL, 0, format, ap_copy);
+    va_end (ap_copy);
+    if (tmp < 0)
+    {
+        g_error ("failed to format log message");
+        return;
+    }
+
+    /* print the message to a variable length array (to avoid malloc) */
+    gchar msg[tmp+1];
+    tmp = g_vsnprintf (msg, sizeof(msg), format, ap);
+    if (tmp < 0)
+    {
+        g_error ("failed to format log message");
+        return;
+    }
+
+    /* log the message with the prefix */
+    g_log (G_LOG_DOMAIN, log_level, "%s%s", pfx, msg);
+}
+
+void
+logger_log (Logger *self, GLogLevelFlags log_level,
+            const gchar *format, ...)
+{
+    va_list ap;
+    va_start (ap, format);
+    logger_logv (self, log_level, format, ap);
+    va_end (ap);
+}

=== added file 'src/logger.h'
--- src/logger.h	1970-01-01 00:00:00 +0000
+++ src/logger.h	2013-08-05 07:39:31 +0000
@@ -0,0 +1,64 @@
+#ifndef LOGGER_H_
+#define LOGGER_H_
+
+#include <glib-object.h>
+
+#ifdef __cplusplus
+#include <cstdarg>  /* for va_list */
+#else
+#include <stdarg.h>  /* for va_list */
+#endif
+
+G_BEGIN_DECLS
+
+#define LOGGER_TYPE (logger_get_type ())
+#define LOGGER(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), LOGGER_TYPE, Logger))
+#define IS_LOGGER(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), LOGGER_TYPE))
+#define LOGGER_GET_INTERFACE(obj) \
+    (G_TYPE_INSTANCE_GET_INTERFACE ((obj), LOGGER_TYPE, LoggerInterface))
+
+typedef struct Logger Logger;
+
+typedef struct {
+    GTypeInterface parent;
+
+    gint (*logprefix) (Logger *self, gchar *buf, gulong buflen);
+    void (*logv) (Logger *self, GLogLevelFlags log_level,
+                  const gchar *format, va_list ap);
+} LoggerInterface;
+
+GType logger_get_type (void);
+
+/*!
+ * \brief instruct \c self to generate a log message prefix
+ *
+ * the semantics of the \c buf and \c buflen arguments and the return
+ * value are the same as g_snprintf()
+ *
+ * there is no default implementation
+ */
+gint logger_logprefix (Logger *self, gchar *buf, gulong buflen);
+
+/*!
+ * \brief instruct \c self to log the given message
+ *
+ * the default implementation prefixes the log message with the
+ * output of logger_logprefix() and then passes the result to
+ * g_log()
+ */
+void logger_logv (Logger *self, GLogLevelFlags log_level,
+                  const gchar *format, va_list ap);
+
+/*! \brief convenience wrapper around \c logger_logv() */
+void logger_log (Logger *self, GLogLevelFlags log_level,
+                 const gchar *format, ...);
+
+/* convenience wrappers around logger_log() */
+#define l_debug(self, ...) \
+    logger_log (LOGGER (self), G_LOG_LEVEL_DEBUG, __VA_ARGS__)
+#define l_warning(self, ...) \
+    logger_log (LOGGER (self), G_LOG_LEVEL_WARNING, __VA_ARGS__)
+
+G_END_DECLS
+
+#endif /* !LOGGER_H_ */

=== modified file 'src/seat-unity.c'
--- src/seat-unity.c	2013-08-05 07:39:31 +0000
+++ src/seat-unity.c	2013-08-05 07:39:31 +0000
@@ -108,13 +108,13 @@
     /* If stopped before it was ready, then revert to VT mode */
     if (!seat->priv->compositor_ready)
     {
-        g_debug ("Compositor failed to start, switching to VT mode");
+        l_debug (seat, "Compositor failed to start, switching to VT mode");
         seat->priv->use_vt_switching = TRUE;
         SEAT_CLASS (seat_unity_parent_class)->start (SEAT (seat));
         return;
     }
 
-    g_debug ("Stopping Unity seat, compositor terminated");
+    l_debug (seat, "Stopping Unity seat, compositor terminated");
 
     seat_stop (SEAT (seat));
 }
@@ -136,7 +136,9 @@
 
          fd = g_open (seat->priv->log_file, O_WRONLY | O_CREAT | O_TRUNC, 0600);
          if (fd < 0)
-             g_warning ("Failed to open log file %s: %s", seat->priv->log_file, g_strerror (errno));
+             l_warning (seat,
+                 "Failed to open log file %s: %s",
+                 seat->priv->log_file, g_strerror (errno));
          else
          {
              dup2 (fd, STDOUT_FILENO);
@@ -161,7 +163,7 @@
 
     errno = 0;
     if (write (seat->priv->to_compositor_pipe[1], data, data_length) != data_length)
-        g_warning ("Failed to write to compositor: %s", strerror (errno));
+        l_warning (seat, "Failed to write to compositor: %s", strerror (errno));
 }
 
 static gboolean
@@ -174,7 +176,7 @@
   
     if (condition == G_IO_HUP)
     {
-        g_debug ("Compositor closed communication channel");
+        l_debug (seat, "Compositor closed communication channel");
         return FALSE;
     }
 
@@ -204,7 +206,8 @@
                                           &n_read,
                                           &error);
         if (error)
-            g_warning ("Failed to read from compositor: %s", error->message);
+            l_warning (seat,
+                "Failed to read from compositor: %s", error->message);
         if (status != G_IO_STATUS_NORMAL)
             return TRUE;
         g_clear_error (&error);
@@ -225,28 +228,30 @@
     switch (id)
     {
     case USC_MESSAGE_PING:
-        g_debug ("PING!");
+        l_debug (seat, "PING!");
         write_message (seat, USC_MESSAGE_PONG, NULL, 0);
         break;
     case USC_MESSAGE_PONG:
-        g_debug ("PONG!");
+        l_debug (seat, "PONG!");
         break;
     case USC_MESSAGE_READY:
-        g_debug ("READY");
+        l_debug (seat, "READY");
         if (!seat->priv->compositor_ready)
         {
             seat->priv->compositor_ready = TRUE;
-            g_debug ("Compositor ready");
+            l_debug (seat, "Compositor ready");
             g_source_remove (seat->priv->compositor_timeout);
             seat->priv->compositor_timeout = 0;
             SEAT_CLASS (seat_unity_parent_class)->start (SEAT (seat));
         }
         break;
     case USC_MESSAGE_SESSION_CONNECTED:
-        g_debug ("SESSION CONNECTED");
+        l_debug (seat, "SESSION CONNECTED");
         break;
     default:
-        g_warning ("Ingoring unknown message %d with %d octets from system compositor", id, payload_length);
+        l_warning (seat,
+            "Ignoring unknown message %d with %d octets from system compositor",
+            id, payload_length);
         break;
     }
 
@@ -310,7 +315,10 @@
             plymouth_quit (TRUE);
         }
         else
-            g_debug ("Plymouth is running on VT %d, but this is less than the configured minimum of %d so not replacing it", active_vt, vt_get_min ());
+            l_debug (seat,
+                "Plymouth is running on VT %d,"
+                " but this is less than the configured minimum of %d"
+                " so not replacing it", active_vt, vt_get_min ());
     }
     if (plymouth_get_is_active ())
         plymouth_quit (FALSE);
@@ -318,7 +326,7 @@
         SEAT_UNITY (seat)->priv->vt = vt_get_unused ();
     if (SEAT_UNITY (seat)->priv->vt < 0)
     {
-        g_debug ("Failed to get a VT to run on");
+        l_debug (seat, "Failed to get a VT to run on");
         return FALSE;
     }
     vt_ref (SEAT_UNITY (seat)->priv->vt);
@@ -326,7 +334,8 @@
     /* Create pipes to talk to compositor */
     if (pipe (SEAT_UNITY (seat)->priv->to_compositor_pipe) < 0 || pipe (SEAT_UNITY (seat)->priv->from_compositor_pipe) < 0)
     {
-        g_debug ("Failed to create compositor pipes: %s", g_strerror (errno));
+        l_debug (seat,
+            "Failed to create compositor pipes: %s", g_strerror (errno));
         return FALSE;
     }
 
@@ -341,7 +350,7 @@
     /* Setup logging */
     dir = config_get_string (config_get_instance (), "LightDM", "log-directory");
     SEAT_UNITY (seat)->priv->log_file = g_build_filename (dir, "unity-system-compositor.log", NULL);
-    g_debug ("Logging to %s", SEAT_UNITY (seat)->priv->log_file);
+    l_debug (seat, "Logging to %s", SEAT_UNITY (seat)->priv->log_file);
     g_free (dir);
 
     SEAT_UNITY (seat)->priv->mir_socket_filename = g_strdup ("/tmp/mir_socket"); // FIXME: Use this socket by default as XMir is hardcoded to this
@@ -372,7 +381,7 @@
     timeout = seat_get_integer_property (seat, "unity-compositor-timeout");
     if (timeout <= 0)
         timeout = 60;
-    g_debug ("Waiting for system compositor for %ds", timeout);
+    l_debug (seat, "Waiting for system compositor for %ds", timeout);
     SEAT_UNITY (seat)->priv->compositor_timeout = g_timeout_add (timeout * 1000, compositor_timeout_cb, seat);
 
     return TRUE;
@@ -386,7 +395,7 @@
     gboolean allow_tcp;
     gint port = 0;
 
-    g_debug ("Starting X server on Unity compositor");
+    l_debug (seat, "Starting X server on Unity compositor");
 
     x_server = x_server_local_new ();
 
@@ -441,7 +450,7 @@
         keys = g_key_file_new ();
         result = g_key_file_load_from_file (keys, path, G_KEY_FILE_NONE, &error);
         if (error)
-            g_debug ("Error getting key %s", error->message);
+            l_debug (seat, "Error getting key %s", error->message);
         g_clear_error (&error);
 
         if (result)
@@ -451,7 +460,7 @@
             if (g_key_file_has_key (keys, "keyring", key_name, NULL))
                 key = g_key_file_get_string (keys, "keyring", key_name, NULL);
             else
-                g_debug ("Key %s not defined", key_name);
+                l_debug (seat, "Key %s not defined", key_name);
 
             if (key)
                 x_server_local_set_xdmcp_key (x_server, key);
@@ -498,7 +507,8 @@
         return create_mir_server (seat);
     else
     {
-        g_warning ("Can't create unsupported display server '%s'", session_type);
+        l_warning (seat,
+            "Can't create unsupported display server '%s'", session_type);
         return NULL;
     }
 }
@@ -507,16 +517,22 @@
 seat_unity_create_greeter_session (Seat *seat)
 {
     Greeter *greeter_session;
+    const gchar *xdg_seat;
 
     greeter_session =
         SEAT_CLASS (seat_unity_parent_class)->create_greeter_session (seat);
-    session_set_env (SESSION (greeter_session), "XDG_SEAT", "seat0");
+    xdg_seat = "seat0";
+    l_debug (seat, "Setting XDG_SEAT=%s", xdg_seat);
+    session_set_env (SESSION (greeter_session), "XDG_SEAT", xdg_seat);
     if (!SEAT_UNITY (seat)->priv->use_vt_switching)
     {
         gchar *value = g_strdup_printf ("%d", SEAT_UNITY (seat)->priv->vt);
+        l_debug (seat, "Setting XDG_VTNR=%s", value);
         session_set_env (SESSION (greeter_session), "XDG_VTNR", value);
         g_free (value);
     }
+    else
+        l_debug (seat, "Not setting XDG_VTNR");
 
     return greeter_session;
 }
@@ -525,15 +541,21 @@
 seat_unity_create_session (Seat *seat)
 {
     Session *session;
+    const gchar *xdg_seat;
 
     session = SEAT_CLASS (seat_unity_parent_class)->create_session (seat);
-    session_set_env (session, "XDG_SEAT", "seat0");
+    xdg_seat = "seat0";
+    l_debug (seat, "Setting XDG_SEAT=%s", xdg_seat);
+    session_set_env (session, "XDG_SEAT", xdg_seat);
     if (!SEAT_UNITY (seat)->priv->use_vt_switching)
     {
         gchar *value = g_strdup_printf ("%d", SEAT_UNITY (seat)->priv->vt);
+        l_debug (seat, "Setting XDG_VTNR=%s", value);
         session_set_env (SESSION (session), "XDG_VTNR", value);
         g_free (value);
     }
+    else
+        l_debug (seat, "Not setting XDG_VTNR");
 
     return session;
 }
@@ -572,11 +594,11 @@
 
         if (id)
         {
-            g_debug ("Switching to Mir session %s", id);
+            l_debug (seat, "Switching to Mir session %s", id);
             write_message (SEAT_UNITY (seat), USC_MESSAGE_SET_ACTIVE_SESSION, (const guint8 *) id, strlen (id));
         }
         else
-            g_warning ("Failed to work out session ID");
+            l_warning (seat, "Failed to work out session ID");
     }
 
     SEAT_CLASS (seat_unity_parent_class)->set_active_session (seat, session);

=== modified file 'src/seat-xlocal.c'
--- src/seat-xlocal.c	2013-07-26 04:52:07 +0000
+++ src/seat-xlocal.c	2013-08-05 07:39:31 +0000
@@ -69,9 +69,9 @@
     gint vt = -1, port = 0;
 
     if (vt > 0)
-        g_debug ("Starting local X display on VT %d", vt);
+        l_debug (seat, "Starting local X display on VT %d", vt);
     else
-        g_debug ("Starting local X display");
+        l_debug (seat, "Starting local X display");
   
     x_server = x_server_local_new ();
 
@@ -95,7 +95,10 @@
             plymouth_deactivate ();
         }
         else
-            g_debug ("Plymouth is running on VT %d, but this is less than the configured minimum of %d so not replacing it", active_vt, vt_get_min ());
+            l_debug (seat,
+                "Plymouth is running on VT %d,"
+                " but this is less than the configured minimum of %d"
+                " so not replacing it", active_vt, vt_get_min ());
     }
     if (plymouth_get_is_active ())
         plymouth_quit (FALSE);
@@ -138,7 +141,7 @@
         keys = g_key_file_new ();
         result = g_key_file_load_from_file (keys, path, G_KEY_FILE_NONE, &error);
         if (error)
-            g_debug ("Error getting key %s", error->message);
+            l_debug (seat, "Error getting key %s", error->message);
         g_clear_error (&error);      
 
         if (result)
@@ -148,7 +151,7 @@
             if (g_key_file_has_key (keys, "keyring", key_name, NULL))
                 key = g_key_file_get_string (keys, "keyring", key_name, NULL);
             else
-                g_debug ("Key %s not defined", key_name);
+                l_debug (seat, "Key %s not defined", key_name);
 
             if (key)
                 x_server_local_set_xdmcp_key (x_server, key);
@@ -166,9 +169,12 @@
 seat_xlocal_create_greeter_session (Seat *seat)
 {
     Greeter *greeter_session;
+    const gchar *xdg_seat;
 
     greeter_session = SEAT_CLASS (seat_xlocal_parent_class)->create_greeter_session (seat);
-    session_set_env (SESSION (greeter_session), "XDG_SEAT", "seat0");
+    xdg_seat = "seat0";
+    l_debug (seat, "Setting XDG_SEAT=%s", xdg_seat);
+    session_set_env (SESSION (greeter_session), "XDG_SEAT", xdg_seat);
 
     return greeter_session;
 }
@@ -177,9 +183,12 @@
 seat_xlocal_create_session (Seat *seat)
 {
     Session *session;
+    const gchar *xdg_seat;
 
     session = SEAT_CLASS (seat_xlocal_parent_class)->create_session (seat);
-    session_set_env (SESSION (session), "XDG_SEAT", "seat0");
+    xdg_seat = "seat0";
+    l_debug (seat, "Setting XDG_SEAT=%s", xdg_seat);
+    session_set_env (SESSION (session), "XDG_SEAT", xdg_seat);
 
     return session;
 }

=== modified file 'src/seat-xremote.c'
--- src/seat-xremote.c	2013-07-24 23:53:37 +0000
+++ src/seat-xremote.c	2013-08-05 07:39:31 +0000
@@ -33,7 +33,9 @@
 
     if (strcmp (session_type, "x") != 0)
     {
-        g_warning ("X remote seat only supports X display servers, not '%s'", session_type);
+        l_warning (seat,
+            "X remote seat only supports X display servers, not '%s'",
+            session_type);
         return NULL;
     }
 
@@ -42,7 +44,7 @@
         hostname = "localhost";
     number = seat_get_integer_property (seat, "xserver-display-number");
 
-    g_debug ("Starting remote X display %s:%d", hostname, number);
+    l_debug (seat, "Starting remote X display %s:%d", hostname, number);
 
     x_server = x_server_remote_new (hostname, number, NULL);
 
@@ -53,9 +55,12 @@
 seat_xremote_create_greeter_session (Seat *seat)
 {
     Greeter *greeter_session;
+    const gchar *xdg_seat;
 
     greeter_session = SEAT_CLASS (seat_xremote_parent_class)->create_greeter_session (seat);
-    session_set_env (SESSION (greeter_session), "XDG_SEAT", "seat0");
+    xdg_seat = "seat0";
+    l_debug (seat, "Setting XDG_SEAT=%s", xdg_seat);
+    session_set_env (SESSION (greeter_session), "XDG_SEAT", xdg_seat);
 
     return greeter_session;
 }
@@ -64,9 +69,12 @@
 seat_xremote_create_session (Seat *seat)
 {
     Session *session;
+    const gchar *xdg_seat;
 
     session = SEAT_CLASS (seat_xremote_parent_class)->create_session (seat);
-    session_set_env (SESSION (session), "XDG_SEAT", "seat0");
+    xdg_seat = "seat0";
+    l_debug (seat, "Setting XDG_SEAT=%s", xdg_seat);
+    session_set_env (SESSION (session), "XDG_SEAT", xdg_seat);
 
     return session;
 }

=== modified file 'src/seat.c'
--- src/seat.c	2013-07-30 14:04:44 +0000
+++ src/seat.c	2013-08-05 07:39:31 +0000
@@ -63,7 +63,11 @@
 #define USER_SERVICE      "lightdm"
 #define AUTOLOGIN_SERVICE "lightdm-autologin"
 
-G_DEFINE_TYPE (Seat, seat, G_TYPE_OBJECT);
+static void seat_logger_iface_init (LoggerInterface *iface);
+
+G_DEFINE_TYPE_WITH_CODE (Seat, seat, G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (
+                             LOGGER_TYPE, seat_logger_iface_init));
 
 typedef struct
 {
@@ -191,7 +195,7 @@
 
         if (IS_GREETER (s))
         {
-            g_debug ("Stopping greeter");
+            l_debug (seat, "Stopping greeter");
             session_stop (s);
         }
     }
@@ -261,7 +265,9 @@
         exit_status = process_get_exit_status (script);
         if (WIFEXITED (exit_status))
         {
-            g_debug ("Exit status of %s: %d", script_name, WEXITSTATUS (exit_status));
+            l_debug (seat,
+                "Exit status of %s: %d",
+                script_name, WEXITSTATUS (exit_status));
             result = WEXITSTATUS (exit_status) == EXIT_SUCCESS;
         }
     }
@@ -299,7 +305,7 @@
         g_list_length (seat->priv->sessions) == 0)
     {
         seat->priv->stopped = TRUE;
-        g_debug ("Seat stopped");
+        l_debug (seat, "Seat stopped");
         g_signal_emit (seat, signals[STOPPED], 0);
     }
 }
@@ -316,7 +322,7 @@
     GList *list, *link;
     Session *active_session;
 
-    g_debug ("Display server stopped");
+    l_debug (seat, "Display server stopped");
 
     g_signal_handlers_disconnect_matched (display_server, G_SIGNAL_MATCH_DATA, 0, 0, NULL, NULL, seat);
     seat->priv->display_servers = g_list_remove (seat->priv->display_servers, display_server);
@@ -344,11 +350,12 @@
             !session_get_is_started (session) &&
             g_list_length (seat->priv->display_servers) == 0)
         {
-            g_debug ("Stopping seat, greeter display server failed to start");
+            l_debug (seat,
+                "Stopping seat, greeter display server failed to start");
             seat_stop (seat);
         }
 
-        g_debug ("Stopping session");
+        l_debug (seat, "Stopping session");
         session_stop (session);
     }
     g_list_free_full (list, g_object_unref);
@@ -359,7 +366,7 @@
         active_session = seat_get_active_session (seat);
         if (!active_session || session_get_display_server (active_session) == display_server)
         {
-            g_debug ("Active display server stopped, starting greeter");
+            l_debug (seat, "Active display server stopped, starting greeter");
             seat_switch_to_greeter (seat);
         }
     }
@@ -396,7 +403,7 @@
         display_server = create_display_server (seat, session_get_session_type (session));
         if (!display_server_start (display_server))
         {
-            g_debug ("Failed to start display server for greeter");
+            l_debug (seat, "Failed to start display server for greeter");
             seat_stop (seat);
         }
 
@@ -431,12 +438,12 @@
 
     if (IS_GREETER (session))
     {
-        g_debug ("Failed to start greeter");
+        l_debug (seat, "Failed to start greeter");
         display_server_stop (session_get_display_server (session));
         return;
     }
 
-    g_debug ("Failed to start session, starting greeter");
+    l_debug (seat, "Failed to start session, starting greeter");
     switch_to_greeter_from_failed_session (seat, session);
 }
 
@@ -451,7 +458,7 @@
         script = seat_get_string_property (seat, "session-setup-script");
     if (script && !run_script (seat, session_get_display_server (session), script, NULL))
     {
-        g_debug ("Switching to greeter due to failed setup script");
+        l_debug (seat, "Switching to greeter due to failed setup script");
         switch_to_greeter_from_failed_session (seat, session);
         return;
     }
@@ -479,17 +486,17 @@
 {
     if (session_get_is_authenticated (session))
     {
-        g_debug ("Session authenticated, running command");
+        l_debug (seat, "Session authenticated, running command");
         run_session (seat, session);
     }
     else if (!IS_GREETER (session))
     {
-        g_debug ("Switching to greeter due to failed authentication");
+        l_debug (seat, "Switching to greeter due to failed authentication");
         switch_to_greeter_from_failed_session (seat, session);
     }
     else
     {
-        g_debug ("Stopping session that failed authentication");
+        l_debug (seat, "Stopping session that failed authentication");
         session_stop (session);
     }
 }
@@ -499,7 +506,7 @@
 {
     DisplayServer *display_server;
 
-    g_debug ("Session stopped");
+    l_debug (seat, "Session stopped");
 
     g_signal_handlers_disconnect_matched (session, G_SIGNAL_MATCH_DATA, 0, 0, NULL, NULL, seat);
     seat->priv->sessions = g_list_remove (seat->priv->sessions, session);
@@ -552,12 +559,13 @@
 
             if (session_get_is_authenticated (s))
             {
-                g_debug ("Greeter stopped, running session");
+                l_debug (seat, "Greeter stopped, running session");
                 run_session (seat, s);
             }
             else
             {
-                g_debug ("Greeter stopped, starting session authentication");
+                l_debug (seat,
+                    "Greeter stopped, starting session authentication");
                 start_session (seat, s);
             }
             break;
@@ -569,13 +577,13 @@
         g_list_length (seat->priv->display_servers) == 1 &&
         g_list_nth_data (seat->priv->display_servers, 0) == display_server)
     {
-        g_debug ("Stopping seat, failed to start a greeter");
+        l_debug (seat, "Stopping seat, failed to start a greeter");
         seat_stop (seat);
     }
     /* If we were the active session, switch to a greeter */
     else if (!IS_GREETER (session) && session == seat_get_active_session (seat))
     {
-        g_debug ("Active session stopped, starting greeter");
+        l_debug (seat, "Active session stopped, starting greeter");
         seat_switch_to_greeter (seat);
     }
 
@@ -595,7 +603,7 @@
         }
         if (n_sessions == 0)
         {
-            g_debug ("Stopping display server, no sessions require it");
+            l_debug (seat, "Stopping display server, no sessions require it");
             display_server_stop (display_server);
         }
     }
@@ -652,7 +660,8 @@
 }
 
 static gchar **
-get_session_argv (SessionConfig *session_config, const gchar *session_wrapper)
+get_session_argv (Seat *seat, SessionConfig *session_config,
+                  const gchar *session_wrapper)
 {
     gboolean result;
     int argc;
@@ -673,7 +682,8 @@
     /* Split command into an array listing and make command absolute */
     result = g_shell_parse_argv (session_config_get_command (session_config), &argc, &argv, &error);
     if (error)
-        g_debug ("Invalid session command '%s': %s", session_config_get_command (session_config), error->message);
+        l_debug (seat, "Invalid session command '%s': %s",
+                 session_config_get_command (session_config), error->message);
     g_clear_error (&error);
     if (!result)
         return NULL;
@@ -688,7 +698,8 @@
 }
 
 static SessionConfig *
-find_session_config (const gchar *sessions_dir, const gchar *session_name)
+find_session_config (Seat *seat, const gchar *sessions_dir,
+                     const gchar *session_name)
 {
     gchar **dirs;
     SessionConfig *session_config = NULL;
@@ -712,7 +723,8 @@
             break;
 
         if (dirs[i+1] == NULL)
-            g_debug ("Failed to find session configuration %s", session_name);
+            l_debug (seat, "Failed to find session configuration %s",
+                     session_name);
         g_clear_error (&error);
     }
     g_strfreev (dirs);
@@ -729,13 +741,13 @@
     SessionConfig *session_config;
     Session *session = NULL;
 
-    g_debug ("Creating user session");
+    l_debug (seat, "Creating user session");
 
     /* Load user preferences */
     user = accounts_get_user_by_name (username);
     if (!user)
     {
-        g_debug ("Can't login unknown user '%s'", username);
+        l_debug (seat, "Can't login unknown user '%s'", username);
         return NULL;
     }
     session_name = user_get_xsession (user);
@@ -744,7 +756,7 @@
     if (!session_name)
         session_name = seat_get_string_property (seat, "user-session");
     sessions_dir = config_get_string (config_get_instance (), "LightDM", "sessions-directory");
-    session_config = find_session_config (sessions_dir, session_name);
+    session_config = find_session_config (seat, sessions_dir, session_name);
     g_free (sessions_dir);
     if (session_config)
     {
@@ -762,14 +774,18 @@
         session_set_pam_service (session, AUTOLOGIN_SERVICE);
         session_set_username (session, username);
         session_set_do_authenticate (session, TRUE);
-        argv = get_session_argv (session_config, seat_get_string_property (seat, "session-wrapper"));
+        argv = get_session_argv (
+            seat, session_config,
+            seat_get_string_property (seat, "session-wrapper"));
         session_set_argv (session, argv);
         g_strfreev (argv);
 
         g_object_unref (session_config);
     }
     else
-        g_debug ("Can't find session '%s'", seat_get_string_property (seat, "user-session"));
+        l_debug (seat,
+            "Can't find session '%s'",
+            seat_get_string_property (seat, "user-session"));
 
 
     g_object_unref (user);
@@ -785,11 +801,14 @@
     Session *session;
 
     sessions_dir = config_get_string (config_get_instance (), "LightDM", "sessions-directory");
-    session_config = find_session_config (sessions_dir, seat_get_string_property (seat, "user-session"));
+    session_config = find_session_config (
+        seat, sessions_dir, seat_get_string_property (seat, "user-session"));
     g_free (sessions_dir);
     if (!session_config)
     {
-        g_debug ("Can't find session '%s'", seat_get_string_property (seat, "user-session"));
+        l_debug (seat,
+            "Can't find session '%s'",
+            seat_get_string_property (seat, "user-session"));
         return NULL;
     }
 
@@ -797,7 +816,9 @@
     session_set_session_type (session, session_config_get_session_type (session_config));
     session_set_do_authenticate (session, TRUE);
     session_set_is_guest (session, TRUE);
-    argv = get_session_argv (session_config, seat_get_string_property (seat, "session-wrapper"));
+    argv = get_session_argv (
+        seat, session_config,
+        seat_get_string_property (seat, "session-wrapper"));
     g_object_unref (session_config);
     session_set_argv (session, argv);
     g_strfreev (argv);
@@ -885,7 +906,7 @@
     existing_session = find_user_session (seat, username);
     if (existing_session && session != existing_session)
     {
-        g_debug ("Returning to existing user session %s", username);
+        l_debug (seat, "Returning to existing user session %s", username);
         session_stop (session);
         seat_set_active_session (seat, existing_session);
         return TRUE;
@@ -916,16 +937,20 @@
     if (user)
         user_set_xsession (session_get_user (session), session_name);
 
-    session_config = find_session_config (sessions_dir, session_name);
+    session_config = find_session_config (seat, sessions_dir, session_name);
     g_free (sessions_dir);
     if (!session_config)
     {
-        g_debug ("Can't find session '%s'", seat_get_string_property (seat, "user-session"));
+        l_debug (seat,
+            "Can't find session '%s'",
+            seat_get_string_property (seat, "user-session"));
         return FALSE;
     }
 
     session_set_session_type (session, session_config_get_session_type (session_config));
-    argv = get_session_argv (session_config, seat_get_string_property (seat, "session-wrapper"));
+    argv = get_session_argv (
+        seat, session_config,
+        seat_get_string_property (seat, "session-wrapper"));
     session_set_argv (session, argv);
     g_strfreev (argv);
     session_set_env (session, "DESKTOP_SESSION", session_name);
@@ -943,7 +968,9 @@
     if (can_share_display_server (seat, display_server) &&
         strcmp (display_server_get_session_type (display_server), session_get_session_type (session)) == 0)
     {
-        g_debug ("Stopping greeter; display server will be re-used for user session");
+        l_debug (seat,
+            "Stopping greeter; display server will be re-used"
+            " for user session");
 
         /* Run on the same display server after the greeter has stopped */
         session_set_display_server (session, display_server);
@@ -960,7 +987,7 @@
         session_set_display_server (session, display_server);
         if (!display_server_start (display_server))
         {
-            g_debug ("Failed to start display server for new session");
+            l_debug (seat, "Failed to start display server for new session");
             return FALSE;
         }
 
@@ -977,15 +1004,16 @@
     gchar *greeter_user;
     const gchar *greeter_wrapper;
 
-    g_debug ("Creating greeter session");
+    l_debug (seat, "Creating greeter session");
 
     sessions_dir = config_get_string (config_get_instance (), "LightDM", "greeters-directory");
-    session_config = find_session_config (sessions_dir, seat_get_string_property (seat, "greeter-session"));
+    session_config = find_session_config (
+        seat, sessions_dir, seat_get_string_property (seat, "greeter-session"));
     g_free (sessions_dir);
     if (!session_config)
         return NULL;
 
-    argv = get_session_argv (session_config, NULL);
+    argv = get_session_argv (seat, session_config, NULL);
     greeter_wrapper = seat_get_string_property (seat, "greeter-wrapper");
     if (greeter_wrapper)
     {
@@ -1052,7 +1080,7 @@
     script = seat_get_string_property (seat, "display-setup-script");
     if (script && !run_script (seat, display_server, script, NULL))
     {
-        g_debug ("Stopping display server due to failed setup script");
+        l_debug (seat, "Stopping display server due to failed setup script");
         display_server_stop (display_server);
         return;
     }
@@ -1069,18 +1097,19 @@
     {
         if (session_get_is_authenticated (session))
         {
-            g_debug ("Display server ready, running session");
+            l_debug (seat, "Display server ready, running session");
             run_session (seat, session);
         }
         else
         {
-            g_debug ("Display server ready, starting session authentication");
+            l_debug (seat,
+                "Display server ready, starting session authentication");
             start_session (seat, session);
         }
     }
     else
     {
-        g_debug ("Stopping not required display server");
+        l_debug (seat, "Stopping not required display server");
         display_server_stop (display_server);
     }
 }
@@ -1090,7 +1119,7 @@
 {
     DisplayServer *display_server;
 
-    g_debug ("Creating display server of type %s", session_type);
+    l_debug (seat, "Creating display server of type %s", session_type);
 
     display_server = SEAT_GET_CLASS (seat)->create_display_server (seat, session_type);
     if (!display_server)
@@ -1133,7 +1162,7 @@
     greeter_session = find_greeter_session (seat);
     if (greeter_session)
     {
-        g_debug ("Switching to existing greeter");
+        l_debug (seat, "Switching to existing greeter");
         seat_set_active_session (seat, SESSION (greeter_session));
         return TRUE;
     }
@@ -1163,12 +1192,12 @@
     if (!seat->priv->can_switch)
         return FALSE;
 
-    g_debug ("Switching to user %s", username);
+    l_debug (seat, "Switching to user %s", username);
 
     session = find_user_session (seat, username);
     if (session)
     {
-        g_debug ("Switching to existing user session %s", username);
+        l_debug (seat, "Switching to existing user session %s", username);
         seat_set_active_session (seat, session);
         return TRUE;
     }
@@ -1219,7 +1248,9 @@
     session = find_guest_session (seat);
     if (session)
     {
-        g_debug ("Switching to existing guest account %s", session_get_username (session));
+        l_debug (seat,
+            "Switching to existing guest account %s",
+            session_get_username (session));
         seat_set_active_session (seat, session);
         return TRUE;
     }
@@ -1252,13 +1283,13 @@
     if (!seat->priv->can_switch)
         return FALSE;
 
-    g_debug ("Locking seat");
+    l_debug (seat, "Locking seat");
 
     /* Switch to greeter if one open (shouldn't be though) */
     greeter_session = find_greeter_session (seat);
     if (greeter_session)
     {
-        g_debug ("Switching to existing greeter");
+        l_debug (seat, "Switching to existing greeter");
         seat_set_active_session (seat, SESSION (greeter_session));
         return TRUE;
     }
@@ -1290,7 +1321,7 @@
     if (seat->priv->stopping)
         return;
 
-    g_debug ("Stopping seat");
+    l_debug (seat, "Stopping seat");
     seat->priv->stopping = TRUE;
     SEAT_GET_CLASS (seat)->stop (seat);
 }
@@ -1322,7 +1353,7 @@
     gboolean autologin_in_background;
     Session *session = NULL, *background_session = NULL;
 
-    g_debug ("Starting seat");
+    l_debug (seat, "Starting seat");
 
     /* If this display server doesn't have a session running on it, just start it */
     if (!get_start_local_sessions (seat))
@@ -1370,7 +1401,8 @@
             session_set_display_server (session, display_server);
             if (!display_server || !display_server_start (display_server))
             {
-                g_debug ("Can't create display server for automatic login");
+                l_debug (seat,
+                    "Can't create display server for automatic login");
                 session_stop (session);
                 if (display_server)
                     display_server_stop (display_server);
@@ -1388,7 +1420,7 @@
         greeter_session = create_greeter_session (seat);
         if (!greeter_session)
         {
-            g_debug ("Failed to create greeter session");
+            l_debug (seat, "Failed to create greeter session");
             return FALSE;
         }
 
@@ -1414,7 +1446,7 @@
         session_set_display_server (session, display_server);
         if (!display_server || !display_server_start (display_server))
         {
-            g_debug ("Can't create display server for greeter");
+            l_debug (seat, "Can't create display server for greeter");
             session_stop (session);
             if (display_server)
                 display_server_stop (display_server);
@@ -1437,7 +1469,8 @@
         background_display_server = create_display_server (seat, session_get_session_type (background_session));
         session_set_display_server (background_session, background_display_server);
         if (!display_server_start (background_display_server))
-            g_warning ("Failed to start display server for background session");
+            l_warning (seat,
+                "Failed to start display server for background session");
     }
 
     seat->priv->started = TRUE;
@@ -1486,7 +1519,7 @@
         DisplayServer *display_server = link->data;
         if (!display_server_get_is_stopping (display_server))
         {
-            g_debug ("Stopping display server");
+            l_debug (seat, "Stopping display server");
             display_server_stop (display_server);
         }
     }
@@ -1499,7 +1532,7 @@
         Session *session = link->data;
         if (!session_get_is_stopping (session))
         {
-            g_debug ("Stopping session");
+            l_debug (seat, "Stopping session");
             session_stop (session);
         }
     }
@@ -1593,3 +1626,17 @@
                       NULL,
                       G_TYPE_NONE, 0);
 }
+
+static gint
+seat_real_logprefix (Logger *self, gchar *buf, gulong buflen)
+{
+    Seat *seat = SEAT (self);
+    return g_snprintf (buf, buflen, "Seat %s: ",
+                       seat_get_string_property (seat, "seat-name"));
+}
+
+static void
+seat_logger_iface_init (LoggerInterface *iface)
+{
+    iface->logprefix = &seat_real_logprefix;
+}

=== modified file 'src/seat.h'
--- src/seat.h	2013-07-25 23:40:02 +0000
+++ src/seat.h	2013-08-05 07:39:31 +0000
@@ -17,6 +17,7 @@
 #include "greeter.h"
 #include "session.h"
 #include "process.h"
+#include "logger.h"
 
 G_BEGIN_DECLS
 

=== modified file 'src/session.c'
--- src/session.c	2013-07-26 02:27:41 +0000
+++ src/session.c	2013-08-05 07:39:31 +0000
@@ -120,7 +120,11 @@
 /* Maximum length of a string to pass between daemon and session */
 #define MAX_STRING_LENGTH 65535
 
-G_DEFINE_TYPE (Session, session, G_TYPE_OBJECT);
+static void session_logger_iface_init (LoggerInterface *iface);
+
+G_DEFINE_TYPE_WITH_CODE (Session, session, G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (
+                             LOGGER_TYPE, session_logger_iface_init));
 
 Session *
 session_new (void)
@@ -338,7 +342,7 @@
 write_data (Session *session, const void *buf, size_t count)
 {
     if (write (session->priv->to_child_input, buf, count) != count)
-        g_warning ("Error writing to session: %s", strerror (errno));
+        l_warning (session, "Error writing to session: %s", strerror (errno));
 }
 
 static void
@@ -382,7 +386,7 @@
     ssize_t n_read;
     n_read = read (session->priv->from_child_output, buf, count);
     if (n_read < 0)
-        g_warning ("Error reading from session: %s", strerror (errno));
+        l_warning (session, "Error reading from session: %s", strerror (errno));
     return n_read;
 }
 
@@ -398,7 +402,7 @@
         return NULL;
     if (length > MAX_STRING_LENGTH)
     {
-        g_warning ("Invalid string length %d from child", length);
+        l_warning (session, "Invalid string length %d from child", length);
         return NULL;
     }
 
@@ -414,17 +418,18 @@
 {
     Session *session = data;
 
-    session->priv->pid = 0;
-
     if (WIFEXITED (status))
-        g_debug ("Session %d exited with return value %d", pid, WEXITSTATUS (status));
+        l_debug (session, "exited with return value %d", WEXITSTATUS (status));
     else if (WIFSIGNALED (status))
-        g_debug ("Session %d terminated with signal %d", pid, WTERMSIG (status));
+        l_debug (session, "terminated with signal %d", WTERMSIG (status));
+
+    /* do this as late as possible for log messages prefix */
+    session->priv->pid = 0;
 
     /* If failed during authentication then report this as an authentication failure */
     if (session->priv->authentication_started && !session->priv->authentication_complete)
     {
-        g_debug ("Session %d failed during authentication", pid);
+        l_debug (session, "failed during authentication");
         session->priv->authentication_complete = TRUE;
         session->priv->authentication_result = PAM_CONV_ERR;
         g_free (session->priv->authentication_result_string);
@@ -473,7 +478,7 @@
     /* Check if authentication completed */
     n_read = read_from_child (session, &auth_complete, sizeof (auth_complete));
     if (n_read < 0)
-        g_debug ("Error reading from child: %s", strerror (errno));
+        l_debug (session, "Error reading from child: %s", strerror (errno));
     if (n_read <= 0)
     {
         session->priv->from_child_watch = 0;
@@ -487,7 +492,10 @@
         g_free (session->priv->authentication_result_string);
         session->priv->authentication_result_string = read_string_from_child (session);
 
-        g_debug ("Session %d authentication complete with return value %d: %s", session->priv->pid, session->priv->authentication_result, session->priv->authentication_result_string);
+        l_debug (session,
+            "authentication complete with return value %d: %s",
+            session->priv->authentication_result,
+            session->priv->authentication_result_string);
 
         /* No longer expect any more messages */
         session->priv->from_child_watch = 0;
@@ -510,7 +518,8 @@
             m->msg = read_string_from_child (session);
         }
 
-        g_debug ("Session %d got %d message(s) from PAM", session->priv->pid, session->priv->messages_length);
+        l_debug (session,
+            "got %d message(s) from PAM", session->priv->messages_length);
 
         g_signal_emit (G_OBJECT (session), signals[GOT_MESSAGES], 0);
     }
@@ -616,7 +625,9 @@
     write_string (session, session->priv->xdisplay);
     write_xauth (session, session->priv->x_authority);
 
-    g_debug ("Started session %d with service '%s', username '%s'", session->priv->pid, session->priv->pam_service, session->priv->username);
+    l_debug (session,
+        "Started with service '%s', username '%s'",
+        session->priv->pam_service, session->priv->username);
 
     return TRUE;
 }
@@ -727,7 +738,7 @@
     session->priv->command_run = TRUE;
 
     command = g_strjoinv (" ", session->priv->argv);
-    g_debug ("Session %d running command %s", session->priv->pid, command);
+    l_debug (session, "running command %s", command);
     g_free (command);
 
     /* Create authority location */
@@ -740,11 +751,15 @@
         g_free (run_dir);
 
         if (g_mkdir_with_parents (dir, S_IRWXU) < 0)
-            g_warning ("Failed to set create system authority dir %s: %s", dir, strerror (errno));          
+            l_warning (session,
+                "Failed to set create system authority dir %s: %s",
+                dir, strerror (errno));
         if (getuid () == 0)
         {
             if (chown (dir, user_get_uid (session_get_user (session)), user_get_gid (session_get_user (session))) < 0)
-                g_warning ("Failed to set ownership of user authority dir: %s", strerror (errno));
+                l_warning (session,
+                    "Failed to set ownership of user authority dir: %s",
+                    strerror (errno));
         }
 
         x_authority_filename = g_build_filename (dir, "xauthority", NULL);
@@ -819,7 +834,7 @@
 
     if (session->priv->pid > 0)
     {
-        g_debug ("Session %d: Sending SIGTERM", session->priv->pid);
+        l_debug (session, "Sending SIGTERM");
         kill (session->priv->pid, SIGTERM);
         // FIXME: Handle timeout
     }
@@ -920,3 +935,19 @@
                       NULL,
                       G_TYPE_NONE, 0);
 }
+
+static gint
+session_real_logprefix (Logger *self, gchar *buf, gulong buflen)
+{
+    Session *session = SESSION (self);
+    if (session->priv->pid != 0)
+        return g_snprintf (buf, buflen, "Session pid=%d: ", session->priv->pid);
+    else
+        return g_snprintf (buf, buflen, "Session (not running): ");
+}
+
+static void
+session_logger_iface_init (LoggerInterface *iface)
+{
+    iface->logprefix = &session_real_logprefix;
+}

=== modified file 'src/session.h'
--- src/session.h	2013-07-26 02:27:41 +0000
+++ src/session.h	2013-08-05 07:39:31 +0000
@@ -21,6 +21,7 @@
 #include "display-server.h"
 #include "accounts.h"
 #include "x-authority.h"
+#include "logger.h"
 
 G_BEGIN_DECLS
 

=== modified file 'src/x-server-local.c'
--- src/x-server-local.c	2013-07-26 01:23:05 +0000
+++ src/x-server-local.c	2013-08-05 07:39:31 +0000
@@ -333,7 +333,9 @@
 
          fd = g_open (server->priv->log_file, O_WRONLY | O_CREAT | O_TRUNC, 0600);
          if (fd < 0)
-             g_warning ("Failed to open log file %s: %s", server->priv->log_file, g_strerror (errno));
+             l_warning (server,
+                 "Failed to open log file %s: %s",
+                 server->priv->log_file, g_strerror (errno));
          else
          {
              dup2 (fd, STDOUT_FILENO);
@@ -352,7 +354,9 @@
     if (signum == SIGUSR1 && !server->priv->got_signal)
     {
         server->priv->got_signal = TRUE;
-        g_debug ("Got signal from X server :%d", x_server_get_display_number (X_SERVER (server)));
+        l_debug (server,
+            "Got signal from X server :%d",
+            x_server_get_display_number (X_SERVER (server)));
 
         // FIXME: Check return value
         DISPLAY_SERVER_CLASS (x_server_local_parent_class)->start (DISPLAY_SERVER (server));
@@ -362,7 +366,7 @@
 static void
 stopped_cb (Process *process, XServerLocal *server)
 {
-    g_debug ("X server stopped");
+    l_debug (server, "X server stopped");
 
     /* Release VT and display number for re-use */
     if (server->priv->have_vt_ref)
@@ -374,7 +378,8 @@
   
     if (x_server_get_authority (X_SERVER (server)) && server->priv->authority_file)
     {
-        g_debug ("Removing X server authority %s", server->priv->authority_file);
+        l_debug (server,
+            "Removing X server authority %s", server->priv->authority_file);
 
         g_unlink (server->priv->authority_file);
 
@@ -404,17 +409,20 @@
         dir = g_build_filename (run_dir, "root", NULL);
         g_free (run_dir);
         if (g_mkdir_with_parents (dir, S_IRWXU) < 0)
-            g_warning ("Failed to make authority directory %s: %s", dir, strerror (errno));
+            l_warning (server,
+                "Failed to make authority directory %s: %s",
+                dir, strerror (errno));
 
         server->priv->authority_file = g_build_filename (dir, x_server_get_address (X_SERVER (server)), NULL);
         g_free (dir);
     }
 
-    g_debug ("Writing X server authority to %s", server->priv->authority_file);
+    l_debug (server,
+        "Writing X server authority to %s", server->priv->authority_file);
 
     x_authority_write (authority, XAUTH_WRITE_MODE_REPLACE, server->priv->authority_file, &error);
     if (error)
-        g_warning ("Failed to write authority: %s", error->message);
+        l_warning (server, "Failed to write authority: %s", error->message);
     g_clear_error (&error);
 }
 
@@ -442,14 +450,16 @@
     filename = g_strdup_printf ("%s.log", display_server_get_name (display_server));
     dir = config_get_string (config_get_instance (), "LightDM", "log-directory");
     server->priv->log_file = g_build_filename (dir, filename, NULL);
-    g_debug ("Logging to %s", server->priv->log_file);
+    l_debug (display_server, "Logging to %s", server->priv->log_file);
     g_free (filename);
     g_free (dir);
 
     absolute_command = get_absolute_command (server->priv->command);
     if (!absolute_command)
     {
-        g_debug ("Can't launch X server %s, not found in path", server->priv->command);
+        l_debug (display_server,
+            "Can't launch X server %s, not found in path",
+            server->priv->command);
         stopped_cb (server->priv->x_server_process, X_SERVER_LOCAL (server));
         return FALSE;
     }
@@ -496,7 +506,7 @@
     process_set_command (server->priv->x_server_process, command->str);
     g_string_free (command, TRUE);
 
-    g_debug ("Launching X Server");
+    l_debug (display_server, "Launching X Server");
 
     /* If running inside another display then pass through those variables */
     if (g_getenv ("DISPLAY"))
@@ -524,7 +534,9 @@
     result = process_start (server->priv->x_server_process, FALSE);
 
     if (result)
-        g_debug ("Waiting for ready signal from X server :%d", x_server_get_display_number (X_SERVER (server)));
+        l_debug (display_server,
+            "Waiting for ready signal from X server :%d",
+            x_server_get_display_number (X_SERVER (server)));
 
     if (!result)
         stopped_cb (server->priv->x_server_process, X_SERVER_LOCAL (server));

=== modified file 'src/x-server-xvnc.c'
--- src/x-server-xvnc.c	2013-07-26 02:27:41 +0000
+++ src/x-server-xvnc.c	2013-08-05 07:39:31 +0000
@@ -144,7 +144,9 @@
 
          fd = g_open (server->priv->log_file, O_WRONLY | O_CREAT | O_TRUNC, 0600);
          if (fd < 0)
-             g_warning ("Failed to open log file %s: %s", server->priv->log_file, g_strerror (errno));
+             l_warning (server,
+                 "Failed to open log file %s: %s",
+                 server->priv->log_file, g_strerror (errno));
          else
          {
              dup2 (fd, STDERR_FILENO);
@@ -162,7 +164,9 @@
     if (signum == SIGUSR1 && !server->priv->got_signal)
     {
         server->priv->got_signal = TRUE;
-        g_debug ("Got signal from Xvnc server :%d", x_server_get_display_number (X_SERVER (server)));
+        l_debug (server,
+            "Got signal from Xvnc server :%d",
+            x_server_get_display_number (X_SERVER (server)));
 
         // FIXME: Check return value
         DISPLAY_SERVER_CLASS (x_server_xvnc_parent_class)->start (DISPLAY_SERVER (server));
@@ -172,14 +176,15 @@
 static void
 stopped_cb (Process *process, XServerXVNC *server)
 {
-    g_debug ("Xvnc server stopped");
+    l_debug (server, "Xvnc server stopped");
 
     g_object_unref (server->priv->x_server_process);
     server->priv->x_server_process = NULL;
 
     x_server_local_release_display_number (x_server_get_display_number (X_SERVER (server)));
 
-    g_debug ("Removing X server authority %s", server->priv->authority_file);
+    l_debug (server,
+        "Removing X server authority %s", server->priv->authority_file);
 
     g_unlink (server->priv->authority_file);
     g_free (server->priv->authority_file);
@@ -219,14 +224,16 @@
     filename = g_strdup_printf ("%s.log", display_server_get_name (display_server));
     dir = config_get_string (config_get_instance (), "LightDM", "log-directory");
     server->priv->log_file = g_build_filename (dir, filename, NULL);
-    g_debug ("Logging to %s", server->priv->log_file);
+    l_debug (display_server, "Logging to %s", server->priv->log_file);
     g_free (filename);
     g_free (dir);
 
     absolute_command = get_absolute_command (server->priv->command);
     if (!absolute_command)
     {
-        g_debug ("Can't launch X server %s, not found in path", server->priv->command);
+        l_debug (display_server,
+            "Can't launch X server %s, not found in path",
+            server->priv->command);
         stopped_cb (server->priv->x_server_process, X_SERVER_XVNC (server));
         return FALSE;
     }
@@ -241,16 +248,20 @@
     dir = g_build_filename (run_dir, "root", NULL);
     g_free (run_dir);
     if (g_mkdir_with_parents (dir, S_IRWXU) < 0)
-        g_warning ("Failed to make authority directory %s: %s", dir, strerror (errno));
+        l_warning (display_server,
+            "Failed to make authority directory %s: %s",
+            dir, strerror (errno));
 
     server->priv->authority_file = g_build_filename (dir, x_server_get_address (X_SERVER (server)), NULL);
     g_free (dir);
 
-    g_debug ("Writing X server authority to %s", server->priv->authority_file);
+    l_debug (display_server,
+        "Writing X server authority to %s", server->priv->authority_file);
 
     x_authority_write (authority, XAUTH_WRITE_MODE_REPLACE, server->priv->authority_file, &error);
     if (error)
-        g_warning ("Failed to write authority: %s", error->message);
+        l_warning (display_server,
+            "Failed to write authority: %s", error->message);
     g_clear_error (&error);
   
     command = g_string_new (absolute_command);
@@ -267,7 +278,7 @@
     process_set_command (server->priv->x_server_process, command->str);
     g_string_free (command, TRUE);
 
-    g_debug ("Launching Xvnc server");
+    l_debug (display_server, "Launching Xvnc server");
 
     /* Variable required for regression tests */
     if (g_getenv ("LIGHTDM_TEST_ROOT"))
@@ -279,7 +290,9 @@
     result = process_start (server->priv->x_server_process, FALSE);
 
     if (result)
-        g_debug ("Waiting for ready signal from Xvnc server :%d", x_server_get_display_number (X_SERVER (server)));
+        l_debug (display_server,
+            "Waiting for ready signal from Xvnc server :%d",
+            x_server_get_display_number (X_SERVER (server)));
 
     if (!result)
         stopped_cb (server->priv->x_server_process, X_SERVER_XVNC (server));

=== modified file 'src/x-server.c'
--- src/x-server.c	2013-07-30 15:56:44 +0000
+++ src/x-server.c	2013-08-05 07:39:31 +0000
@@ -133,11 +133,12 @@
     }
 
     /* Open connection */  
-    g_debug ("Connecting to XServer %s", x_server_get_address (server));
+    l_debug (server, "Connecting to XServer %s", x_server_get_address (server));
     server->priv->connection = xcb_connect_to_display_with_auth_info (x_server_get_address (server), auth, NULL);
     if (xcb_connection_has_error (server->priv->connection))
     {
-        g_debug ("Error connecting to XServer %s", x_server_get_address (server));
+        l_debug (server,
+            "Error connecting to XServer %s", x_server_get_address (server));
         return FALSE;
     }
 
@@ -161,9 +162,12 @@
         g_free (t);
 
         t = g_strdup_printf ("%d", vt);
+        l_debug (session, "Setting XDG_VTNR=%s", t);
         session_set_env (session, "XDG_VTNR", t);
         g_free (t);
     }
+    else
+        l_debug (session, "Not setting XDG_VTNR");
 
     session_set_env (session, "DISPLAY", x_server_get_address (X_SERVER (display_server)));
     session_set_tty (session, x_server_get_address (X_SERVER (display_server)));