bus: add new sd_bus_creds object to encapsulate process credentials

This way we can unify handling of credentials that are attached to
messages, or can be queried for bus name owners or connection peers.

This also adds the ability to extend incomplete credential information
with data from /proc,

Also, provide a convenience call that will automatically determine the
most appropriate credential object for an incoming message, by using the
the attached information if possible, the sending name information if
available and otherwise the peer's credentials.

src/machine/machine-dbus.c

@@ -154,6 +154,7 @@ int machine_object_find(sd_bus *bus, const char *path, const char *interface, vo
         assert(m);
 
         if (streq(path, "/org/freedesktop/machine1/machine/self")) {
+                _cleanup_bus_creds_unref_ sd_bus_creds *creds = NULL;
                 sd_bus_message *message;
                 pid_t pid;
 
@@ -161,9 +162,13 @@ int machine_object_find(sd_bus *bus, const char *path, const char *interface, vo
                 if (!message)
                         return 0;
 
-                r = sd_bus_get_owner_pid(bus, sd_bus_message_get_sender(message), &pid);
+                r = sd_bus_query_sender_creds(message, SD_BUS_CREDS_PID, &creds);
                 if (r < 0)
-                        return 0;
+                        return r;
+
+                r = sd_bus_creds_get_pid(creds, &pid);
+                if (r < 0)
+                        return r;
 
                 r = manager_get_machine_by_pid(m, pid, &machine);
                 if (r <= 0)

src/machine/machined-dbus.c

@@ -102,7 +102,13 @@ static int method_get_machine_by_pid(sd_bus *bus, sd_bus_message *message, void
                 return r;
 
         if (pid == 0) {
-                r = sd_bus_get_owner_pid(bus, sd_bus_message_get_sender(message), &pid);
+                _cleanup_bus_creds_unref_ sd_bus_creds *creds = NULL;
+
+                r = sd_bus_query_sender_creds(message, SD_BUS_CREDS_PID, &creds);
+                if (r < 0)
+                        return r;
+
+                r = sd_bus_creds_get_pid(creds, &pid);
                 if (r < 0)
                         return r;
         }
@@ -216,9 +222,15 @@ static int method_create_machine(sd_bus *bus, sd_bus_message *message, void *use
                 return r;
 
         if (leader == 0) {
+                _cleanup_bus_creds_unref_ sd_bus_creds *creds = NULL;
+
+                r = sd_bus_query_sender_creds(message, SD_BUS_CREDS_PID, &creds);
+                if (r < 0)
+                        return r;
+
                 assert_cc(sizeof(uint32_t) == sizeof(pid_t));
 
-                r = sd_bus_get_owner_pid(bus, sd_bus_message_get_sender(message), (pid_t*) &leader);
+                r = sd_bus_creds_get_pid(creds, (pid_t*) &leader);
                 if (r < 0)
                         return r;
         }