dmeventd: event string parser handles empty field

Improve event string parser to avoid unneeded alloc+free.

Daemon talk function uses '-' to mark NULL/missing field.
So restore the NULL pointer back on parser.

This should have made old tools like 'dmevent_tool' work again.
As now 'uuid' or 'dso' could become NULL and then be
properly used in _want_registered_device() function.

Since lvm2 always fill these parameters, this change should
have no effect on lvm2.

2 files changed, 32 insertions, 17 deletions

diff --git a/WHATS_NEW_DM b/WHATS_NEW_DM
index e09ab6394..961aec5ef 100644
--- a/WHATS_NEW_DM
+++ b/WHATS_NEW_DM
@@ -1,5 +1,6 @@
 Version 1.02.110 - 
 ======================================
+  Fix/restore parsing of empty field '-' when processing dmeventd event.
   Enhance dm_tree_node_size_changed() to recognize size reduction.
   Support exit on idle for dmenventd (1 hour).
   Add support to allow unmonitor device from plugin itself.
diff --git a/daemons/dmeventd/dmeventd.c b/daemons/dmeventd/dmeventd.c
index d6accbfea..42c724b8f 100644
--- a/daemons/dmeventd/dmeventd.c
+++ b/daemons/dmeventd/dmeventd.c
@@ -473,34 +473,48 @@ static int _pthread_create_smallstack(pthread_t *t, void *(*fun)(void *), void *
 
 /*
  * Fetch a string off src and duplicate it into *ptr.
- * Pay attention to zero-length strings.
+ * Pay attention to zero-length and 'empty' strings ('-').
  */
 /* FIXME? move to libdevmapper to share with the client lib (need to
    make delimiter a parameter then) */
 static int _fetch_string(char **ptr, char **src, const int delimiter)
 {
-	int ret = 0;
+	int ret = 1;
 	char *p;
 	size_t len;
+	*ptr = NULL; /* Empty field returns NULL pointer */
 
-	if ((p = strchr(*src, delimiter)))
-		*p = 0;
-
-	if ((*ptr = dm_strdup(*src))) {
-		if ((len = strlen(*ptr)))
-			*src += len;
-		else {
-			dm_free(*ptr);
-			*ptr = NULL;
+	if ((*src)[0] == '-') {
+		/* Could be empty field '-', handle without allocation */
+		if ((*src)[1] == '\0') {
+			(*src)++;
+			goto out;
+		} else if ((*src)[1] == delimiter) {
+			(*src) += 2;
+			goto out;
 		}
-
-		(*src)++;
-		ret = 1;
 	}
 
-	if (p)
-		*p = delimiter;
-
+	if ((p = strchr(*src, delimiter))) {
+		if (*src < p) {
+			*p = 0; /* Temporary exit with \0 */
+			if (!(*ptr = dm_strdup(*src))) {
+				log_error("Failed to fetch item %s.", *src);
+				ret = 0; /* Allocation fail */
+			}
+			*p = delimiter;
+			*src = p;
+		}
+		(*src)++; /* Skip delmiter, next field */
+	} else if ((len = strlen(*src))) {
+		/* No delimiter, item ends with '\0' */
+		if (!(*ptr = dm_strdup(*src))) {
+			log_error("Failed to fetch last item %s.", *src);
+			ret = 0; /* Fail */
+		}
+		*src += len + 1;
+	}
+out:
 	return ret;
 }