attach: introduce explicit personality macro

src/lxc/attach.c

@@ -1147,7 +1147,7 @@ __noreturn static void do_attach(struct attach_payload *ap)
 	if (options->attach_flags & LXC_ATTACH_SET_PERSONALITY) {
 		long new_personality;
 
-		if (options->personality < 0)
+		if (options->personality == LXC_ATTACH_DETECT_PERSONALITY)
 			new_personality = ctx->personality;
 		else
 			new_personality = options->personality;

src/lxc/attach_options.h

@@ -82,6 +82,8 @@ typedef struct lxc_groups_t {
 	gid_t *list;
 } lxc_groups_t;
 
+#define LXC_ATTACH_DETECT_PERSONALITY ~0L
+
 /*!
  * LXC attach options for \ref lxc_container \c attach().
  */
@@ -92,7 +94,7 @@ typedef struct lxc_attach_options_t {
 	/*! The namespaces to attach to (CLONE_NEW... flags) */
 	int namespaces;
 
-	/*! Initial personality (\c -1 to autodetect).
+	/*! Initial personality (\c LXC_ATTACH_DETECT_PERSONALITY to autodetect).
 	 * \warning This may be ignored if lxc is compiled without personality
 	 * support)
 	 */
@@ -160,7 +162,7 @@ typedef struct lxc_attach_options_t {
 	{                                               		\
 		.attach_flags	= LXC_ATTACH_DEFAULT,   		\
 		.namespaces	= -1,					\
-		.personality	= -1,			\
+		.personality	= LXC_ATTACH_DETECT_PERSONALITY,	\
 		.initial_cwd	= NULL,					\
 		.uid		= (uid_t)-1,            		\
 		.gid		= (gid_t)-1,            		\