log: support strings as level selectors in WIREPLUMBER_DEBUG

This allows for WIREPLUMBER_DEBUG="D" which avoids users having to
remember which numerical value the various levels have. The strings to
select are the ones printed by the logger, i.e. UECWMIDT.

docs/rst/daemon-logging.rst

@@ -10,7 +10,8 @@ Getting debug messages on the command line is a matter of setting the
 
    WIREPLUMBER_DEBUG=level:category1,category2,...
 
-``level`` can be a number from 1 to 5 and defines the minimum debug level to show:
+``level`` can be one of ``CEWMIDT`` or a numerical log level as listed below.
+In either case it defines the minimum debug level to show:
 
   0. critical warnings and fatal errors (``C`` & ``E`` in the log)
   1. warnings (``W``)
@@ -50,13 +51,13 @@ Show all messages:
 
 .. code::
 
-   WIREPLUMBER_DEBUG=5
+   WIREPLUMBER_DEBUG=D
 
 Show all messages up to the *debug* level (E, C, W, M, I & D), excluding *trace*:
 
 .. code::
 
-   WIREPLUMBER_DEBUG=4
+   WIREPLUMBER_DEBUG=M
 
 Show all messages up to the *message* level (E, C, W & M),
 excluding *info*, *debug* & *trace*
@@ -70,13 +71,13 @@ Show all messages from the wireplumber library:
 
 .. code::
 
-   WIREPLUMBER_DEBUG=5:wp-*
+   WIREPLUMBER_DEBUG=D:wp-*
 
 Show all messages from ``wp-registry``, libpipewire and all modules:
 
 .. code::
 
-   WIREPLUMBER_DEBUG=5:wp-registry,pw,m-*
+   WIREPLUMBER_DEBUG=D:wp-registry,pw,m-*
 
 Relationship with the GLib log handler & G_MESSAGES_DEBUG
 ---------------------------------------------------------

lib/wp/log.c

@@ -379,6 +379,19 @@ wp_log_level_is_enabled (GLogLevelFlags log_level)
   return log_level_index (log_level) <= enabled_level;
 }
 
+static gint
+level_index_from_string (const char *str)
+{
+  g_return_val_if_fail (str != NULL, 0);
+
+  for (guint i = 0; i < G_N_ELEMENTS (log_level_info); i++) {
+    if (g_str_equal (str, log_level_info[i].name))
+      return i;
+  }
+
+  return level_index_from_spa (atoi (str));
+}
+
 /*!
  * \brief Configures the log level and enabled categories
  * \ingroup wplog
@@ -406,7 +419,7 @@ wp_log_set_level (const gchar * level_str)
     tokens = pw_split_strv (level_str, ":", 2, &n_tokens);
 
     /* set the log level */
-    enabled_level = level_index_from_spa (atoi (tokens[0]));
+    enabled_level = level_index_from_string (tokens[0]);
 
     /* enable filtering of debug categories */
     if (n_tokens > 1) {