[dm-devel] [PATCH v3 13/21] libmultipath: provide defaults for {get, put}_multipath_config

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

Add an implementation of get_multipath_config() and put_multipath_config()
to libmultipath. The linker's symbol lookup rules will make sure that
applications can override these functions if they need to. Defining
these functions in libmultipath avoids the need to provide stubs
for these functions in every appliation linking to libmultipath.

libmultipath's internal functions simply refer to a static "struct config".
It must be initialized with init_config() rather than load_config(),
which always allocates a new struct for backward compatibility, and must
be teared down using uninit_config().

Reviewed-by: Benjamin Marzinski <bmarzins at redhat.com>
Signed-off-by: Martin Wilck <mwilck at suse.com>
---
 libmultipath/config.c             | 75 ++++++++++++++++++++++++++-----
 libmultipath/config.h             | 21 +++++++--
 libmultipath/libmultipath.version | 10 +++++
 3 files changed, 93 insertions(+), 13 deletions(-)

diff --git a/libmultipath/config.c b/libmultipath/config.c
index 5c91a09..01b77df 100644
--- a/libmultipath/config.c
+++ b/libmultipath/config.c
@@ -27,6 +27,26 @@
 #include "mpath_cmd.h"
 #include "propsel.h"
 
+static struct config __internal_config;
+struct config *libmp_get_multipath_config(void)
+{
+	if (!__internal_config.hwtable)
+		/* not initialized */
+		return NULL;
+	return &__internal_config;
+}
+
+struct config *get_multipath_config(void)
+	__attribute__((weak, alias("libmp_get_multipath_config")));
+
+void libmp_put_multipath_config(void *conf __attribute__((unused)))
+{
+	/* empty */
+}
+
+void put_multipath_config(void *conf)
+	__attribute__((weak, alias("libmp_put_multipath_config")));
+
 static int
 hwe_strmatch (const struct hwentry *hwe1, const struct hwentry *hwe2)
 {
@@ -574,17 +594,15 @@ restart:
 	return;
 }
 
-struct config *
-alloc_config (void)
+static struct config *alloc_config (void)
 {
 	return (struct config *)MALLOC(sizeof(struct config));
 }
 
-void
-free_config (struct config * conf)
+static void _uninit_config(struct config *conf)
 {
 	if (!conf)
-		return;
+		conf = &__internal_config;
 
 	if (conf->multipath_dir)
 		FREE(conf->multipath_dir);
@@ -650,7 +668,27 @@ free_config (struct config * conf)
 	free_hwtable(conf->hwtable);
 	free_hwe(conf->overrides);
 	free_keywords(conf->keywords);
-	FREE(conf);
+
+	memset(conf, 0, sizeof(*conf));
+}
+
+void uninit_config(void)
+{
+	_uninit_config(&__internal_config);
+}
+
+void free_config(struct config *conf)
+{
+	if (!conf)
+		return;
+	else if (conf == &__internal_config) {
+		condlog(0, "ERROR: %s called for internal config. Use uninit_config() instead",
+			__func__);
+		return;
+	}
+
+	_uninit_config(conf);
+	free(conf);
 }
 
 /* if multipath fails to process the config directory, it should continue,
@@ -719,12 +757,29 @@ static void set_max_checkint_from_watchdog(struct config *conf)
 }
 #endif
 
+static int _init_config (const char *file, struct config *conf);
+
+int init_config(const char *file)
+{
+	return _init_config(file, &__internal_config);
+}
+
 struct config *load_config(const char *file)
 {
 	struct config *conf = alloc_config();
 
+	if (conf && !_init_config(file, conf))
+		return conf;
+
+	free(conf);
+	return NULL;
+}
+
+int _init_config (const char *file, struct config *conf)
+{
+
 	if (!conf)
-		return NULL;
+		conf = &__internal_config;
 
 	/*
 	 * internal defaults
@@ -896,10 +951,10 @@ struct config *load_config(const char *file)
 	    !conf->wwids_file || !conf->prkeys_file)
 		goto out;
 
-	return conf;
+	return 0;
 out:
-	free_config(conf);
-	return NULL;
+	_uninit_config(conf);
+	return 1;
 }
 
 char *get_uid_attribute_by_attrs(struct config *conf,
diff --git a/libmultipath/config.h b/libmultipath/config.h
index ace403b..0329de2 100644
--- a/libmultipath/config.h
+++ b/libmultipath/config.h
@@ -252,10 +252,25 @@ void free_mptable (vector mptable);
 int store_hwe (vector hwtable, struct hwentry *);
 
 struct config *load_config (const char *file);
-struct config * alloc_config (void);
 void free_config (struct config * conf);
-extern struct config *get_multipath_config(void);
-extern void put_multipath_config(void *);
+int init_config(const char *file);
+void uninit_config(void);
+
+/*
+ * libmultipath provides default implementations of
+ * get_multipath_config() and put_multipath_config().
+ * Applications using these should use init_config(file, NULL)
+ * to load the configuration, rather than load_config(file).
+ * Likewise, uninit_config() should be used for teardown, but
+ * using free_config() for that is supported, too.
+ * Applications can define their own {get,put}_multipath_config()
+ * functions, which override the library-internal ones, but
+ * could still call libmp_{get,put}_multipath_config().
+ */
+struct config *libmp_get_multipath_config(void);
+struct config *get_multipath_config(void);
+void libmp_put_multipath_config(void *);
+void put_multipath_config(void *);
 
 int parse_uid_attrs(char *uid_attrs, struct config *conf);
 char *get_uid_attribute_by_attrs(struct config *conf,
diff --git a/libmultipath/libmultipath.version b/libmultipath/libmultipath.version
index 97acdbb..3e780fc 100644
--- a/libmultipath/libmultipath.version
+++ b/libmultipath/libmultipath.version
@@ -251,3 +251,13 @@ global:
 	libmp_dm_task_run;
 	cleanup_mutex;
 } LIBMULTIPATH_2.0.0;
+
+LIBMULTIPATH_2.2.0 {
+global:
+	libmp_get_multipath_config;
+	get_multipath_config;
+	libmp_put_multipath_config;
+	put_multipath_config;
+	init_config;
+	uninit_config;
+} LIBMULTIPATH_2.1.0;
-- 
2.28.0