[PATCH spice-common 3/4] RFC: Add spice log categories

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From: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>

A log category is defined with SPICE_LOG_CATEGORY(). The macro will
register a structure with a constructor (and unregister it on
unloading with a destructor).

spice_log_init() must be called at initialization time, to set enabled
categories and add the 'Spice' glib domain to G_MESSAGES_DEBUG (NB: if
useful, we could have other log domains automatically associated with
categories and enable them too).

A category can be enabled with SPICE_DEBUG="cat_name foo*" (*? are
accepted glob-like wildcards). All categories are enabled with
SPICE_DEBUG=1 or 'all'. To list available categories, you can run the
program with SPICE_DEBUG=help.

spice_log() will log the debug message using structured logging if
available (or fallback on regular glog). The associated Spice log in
the journal will have the SPICE_LOG_CATEGORY field set accordingly.

If deemed necessary, you can also avoid expensive log computation with
SPICE_LOG_ENABLED() macro help.

TODO: add tests

Signed-off-by: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
---
 common/log.c         | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
 common/log.h         | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 tests/test-logging.c |  1 +
 3 files changed, 139 insertions(+), 1 deletion(-)

diff --git a/common/log.c b/common/log.c
index 6a15a30..029e279 100644
--- a/common/log.c
+++ b/common/log.c
@@ -18,3 +18,70 @@
 #ifdef HAVE_CONFIG_H
 #include <config.h>
 #endif
+
+#include "log.h"
+
+static GSList *log_categories = NULL; /* all registered log categories */
+
+void spice_log_category_register(SpiceLogCategory *cat)
+{
+    if (!g_slist_find(log_categories, cat)) {
+        log_categories = g_slist_prepend(log_categories, cat);
+    }
+}
+
+void spice_log_category_unregister(SpiceLogCategory *cat)
+{
+    log_categories = g_slist_remove(log_categories, cat);
+}
+
+void spice_log_init(void)
+{
+    bool all = false;
+    const char *env = g_getenv("SPICE_DEBUG");
+    const char *genv = g_getenv("G_MESSAGES_DEBUG");
+
+    if (g_strcmp0(env, "help") == 0) {
+        g_printerr("SPICE_DEBUG=1 or 'all' to enable all debug\n");
+        g_printerr("SPICE_DEBUG=\"cat1* cat2\" to enable specific categories\n");
+        g_printerr("Available Spice debug categories:\n");
+        for (GSList *l = log_categories; l != NULL; l = g_slist_next(l)) {
+            SpiceLogCategory *cat = l->data;
+            g_printerr("%-20s - %s\n", cat->name, cat->desc);
+        }
+        return;
+    }
+
+    /* Make sure GLib default log handler will show the debug
+     * messages. Messing with environment variables like this is
+     * rather ugly, but done for historical reasons.
+     */
+    if (env && *env != '\0') {
+        if (genv == NULL) {
+            g_setenv("G_MESSAGES_DEBUG", G_LOG_DOMAIN, TRUE);
+        } else if (!g_str_equal(genv, "all")) {
+            char *new_env = g_strconcat(genv, " ", G_LOG_DOMAIN, NULL);
+            g_setenv("G_MESSAGES_DEBUG", new_env, TRUE);
+            g_free(new_env);
+        }
+    }
+
+    all = g_strcmp0(env, "1") == 0 || g_strcmp0(env, "all") == 0;
+    if (all) {
+        for (GSList *l = log_categories; l != NULL; l = g_slist_next(l)) {
+            SpiceLogCategory *cat = l->data;
+            cat->enabled = true;
+        }
+    } else if (env) {
+        char **cat_sel = g_strsplit(env, " ", -1);
+        for (char **strv = cat_sel; *strv != NULL; strv++) {
+            GPatternSpec *pat = g_pattern_spec_new(*strv);
+            for (GSList *l = log_categories; l != NULL; l = g_slist_next(l)) {
+                SpiceLogCategory *cat = l->data;
+                cat->enabled = g_pattern_match_string(pat, cat->name);
+            }
+            g_pattern_spec_free(pat);
+        }
+        g_strfreev(cat_sel);
+    }
+}
diff --git a/common/log.h b/common/log.h
index b86fd08..e202563 100644
--- a/common/log.h
+++ b/common/log.h
@@ -28,6 +28,63 @@
 
 G_BEGIN_DECLS
 
+typedef struct SpiceLogCategory {
+    const char *name;
+    const char *desc;
+    bool enabled;
+} SpiceLogCategory;
+
+/* This is only useful if the category is shared in several units. */
+/* The code could probably be better organized instead. */
+#define SPICE_LOG_CATEGORY_DECLARE(Name)                        \
+    extern SpiceLogCategory G_PASTE(spice_log_category_, Name);
+
+#define SPICE_LOG_CATEGORY(Name, Desc)                                  \
+    SpiceLogCategory G_PASTE(spice_log_category_, Name) = {             \
+        .name = G_STRINGIFY(Name),                                      \
+        .desc = Desc,                                                   \
+        .enabled = false,                                               \
+    };                                                                  \
+    SPICE_CONSTRUCTOR_FUNC(G_PASTE(spice_log_category_ctor_, Name)) {   \
+        spice_log_category_register(&G_PASTE(spice_log_category_, Name)); \
+    }                                                                   \
+    SPICE_DESTRUCTOR_FUNC(G_PASTE(spice_log_category_dtor_, Name)) {    \
+        spice_log_category_unregister(&G_PASTE(spice_log_category_, Name)); \
+    }
+
+#define SPICE_LOG_ENABLED(Name)                                 \
+    G_UNLIKELY(G_PASTE(spice_log_category_, Name).enabled)
+
+#if G_LOG_USE_STRUCTURED
+/* override future deprecation warning */
+#define g_log_structured(Domain, Level, ...) G_STMT_START {     \
+    G_GNUC_BEGIN_IGNORE_DEPRECATIONS                            \
+        g_log_structured(Domain, Level, ## __VA_ARGS__);        \
+    G_GNUC_END_IGNORE_DEPRECATIONS                              \
+} G_STMT_END
+
+#define spice_log(Name, Msg, ...) G_STMT_START {                        \
+    if (SPICE_LOG_ENABLED(Name)) {                                      \
+        g_log_structured(G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG,               \
+                         "CODE_FILE", __FILE__,                         \
+                         "CODE_LINE", G_STRINGIFY(__LINE__),            \
+                         "CODE_FUNC", G_STRFUNC,                        \
+                         "SPICE_LOG_CATEGORY", G_STRINGIFY(Name),       \
+                         "MESSAGE", G_STRINGIFY(Name)": " Msg, ## __VA_ARGS__); \
+    }                                                                   \
+} G_STMT_END
+#else /* !G_LOG_USE_STRUCTURED */
+#define spice_log(Name, Msg, ...) G_STMT_START {                \
+    if (SPICE_LOG_ENABLED(Name)) {                              \
+        g_debug(G_STRINGIFY(Name)": " Msg, ## __VA_ARGS__);     \
+    }                                                           \
+} G_STMT_END
+#endif
+
+void spice_log_category_register(SpiceLogCategory *cat);
+void spice_log_category_unregister(SpiceLogCategory *cat);
+void spice_log_init(void);
+
 /* deprecated, please use glib directly */
 #define spice_return_if_fail(x) g_return_if_fail(x)
 #define spice_return_val_if_fail(x, val) g_return_val_if_fail(x, val)
@@ -36,7 +93,7 @@ G_BEGIN_DECLS
 #define spice_assert(x) g_assert(x)
 #define spice_static_assert(x) G_STATIC_ASSERT(x)
 
-/* deprecated */
+/* deprecated, use spice_log() instead */
 #ifndef SPICE_LOG_DOMAIN
 #define SPICE_LOG_DOMAIN __FILE__
 #endif
@@ -61,7 +118,20 @@ static inline void _spice_debug(const char *domain, const char *file,
     if (msg) {
         g_string_append_vprintf(s, msg, args);
     }
+#if G_LOG_USE_STRUCTURED
+    G_GNUC_BEGIN_IGNORE_DEPRECATIONS
+    const GLogField fields[] = {
+        { "GLIB_DOMAIN", G_LOG_DOMAIN, -1 },
+        { "MESSAGE", s->str, -1 },
+        { "CODE_FILE", file, -1 },
+        { "CODE_LINE", line, -1 },
+        { "CODE_FUNC", func, -1 },
+    };
+    g_log_structured_array(G_LOG_LEVEL_DEBUG, fields, G_N_ELEMENTS(fields));
+    G_GNUC_END_IGNORE_DEPRECATIONS
+#else
     g_debug("%s", s->str);
+#endif
     va_end(args);
     g_string_free(s, true);
 }
diff --git a/tests/test-logging.c b/tests/test-logging.c
index 03f367a..cfe63e4 100644
--- a/tests/test-logging.c
+++ b/tests/test-logging.c
@@ -87,6 +87,7 @@ int main(int argc, char **argv)
     fatal_mask = (GLogLevelFlags)g_log_set_always_fatal((GLogLevelFlags) G_LOG_FATAL_MASK);
 
     g_test_init(&argc, &argv, NULL);
+    spice_log_init();
 
     /* Reset fatal mask set by g_test_init() as we don't want
      * warnings/criticals to be fatal by default since this is what some of the
-- 
2.13.0.91.g00982b8dd

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