Add mxs_strerror

Thread-safe version of strerror; thread local buffer used for storing
the message. The performance penalty of a thread local buffer is not
likely to be significant, since this is only called in an error
situation that anyway is likely to interrupt the normal processing.

include/maxscale/log_manager.h

@@ -196,4 +196,21 @@ enum
                                     trailing NULL. If longer, it will be cut. */
 };
 
+/**
+ * Return a thread specific pointer to a string describing the error
+ * code passed as argument. The string is obtained using strerror_r.
+ *
+ * @param error  One of the errno error codes.
+ *
+ * @return Thread specific pointer to string describing the error code.
+ *
+ * @attention The function is thread safe, but not re-entrant. That is,
+ * calling it twice with different error codes between two sequence points
+ * will not work. E.g:
+ *
+ *     printf("EINVAL = %s, EACCESS = %s",
+ *            mxs_strerror(EINVAL), mxs_strerror(EACCESS));
+ */
+const char* mxs_strerror(int error);
+
 MXS_END_DECLS

server/core/log_manager.cc

@@ -24,6 +24,7 @@
 #include <errno.h>
 #include <syslog.h>
 #include <maxscale/atomic.h>
+#include <maxscale/platform.h>
 
 #include <maxscale/hashtable.h>
 #include <maxscale/spinlock.h>
@@ -3011,3 +3012,10 @@ int mxs_log_message(int priority,
 
     return err;
 }
+
+const char* mxs_strerror(int error)
+{
+    static thread_local char errbuf[MXS_STRERROR_BUFLEN];
+
+    return strerror_r(error, errbuf, sizeof(errbuf));
+}