u-a: When changing slave links do not warn that the link group is broken

When new slave links are added or the targets for existing ones are
changed, we should not give bogus and confusing warnings as if the link
group was broken on disk and needs to be updated. Instead detect these
cases and give an informative message noting that the link group needs
to be updated due to the slave links changes. But still warn in case any
of the slaves is not being updated and is trully broken.

debian/changelog

@@ -44,6 +44,9 @@ dpkg (1.17.2) UNRELEASED; urgency=low
     Reported by Shawn Landden <shawnlandden@gmail.com>.
   * Recognize «start-stop-daemon -C» as documented. Closes: #719746
     Reported by Brian S. Julin <bri@abrij.org>.
+  * When update-alternatives is told to change slave links, do not warn that
+    the link group is broken, just print a notice that the alternative is
+    being updated due to the changes.
 
   [ Updated programs translations ]
   * German (Sven Joachim).

utils/update-alternatives.c

@@ -634,6 +634,7 @@ struct slave_link {
 	struct slave_link *next;
 	char *name;
 	char *link;
+	bool updated;
 };
 
 struct commit_operation {
@@ -649,6 +650,12 @@ struct commit_operation {
 	char *arg_b;
 };
 
+enum alternative_update_reason {
+	ALT_UPDATE_NO,
+	ALT_UPDATE_SLAVE_CHANGED,
+	ALT_UPDATE_LINK_BROKEN,
+};
+
 struct alternative {
 	char *master_name;
 	char *master_link;
@@ -945,7 +952,7 @@ alternative_add_choice(struct alternative *a, struct fileset *fs)
 }
 
 /* slave_name and slave_link must be allocated with malloc */
-static void
+static struct slave_link *
 alternative_add_slave(struct alternative *a, char *slave_name,
                       char *slave_link)
 {
@@ -956,7 +963,7 @@ alternative_add_slave(struct alternative *a, char *slave_name,
 		if (strcmp(sl->name, slave_name) == 0) {
 			free(sl->link);
 			sl->link = xstrdup(slave_link);
-			return;
+			return sl;
 		}
 		if (sl->next == NULL)
 			break;
@@ -966,17 +973,23 @@ alternative_add_slave(struct alternative *a, char *slave_name,
 	new = xmalloc(sizeof(*new));
 	new->name = slave_name;
 	new->link = slave_link;
+	new->updated = false;
 	new->next = NULL;
 	if (sl)
 		sl->next = new;
 	else
 		a->slaves = new;
+
+	return sl;
 }
 
 static void
 alternative_copy_slave(struct alternative *a, struct slave_link *sl)
 {
-	alternative_add_slave(a, xstrdup(sl->name), xstrdup(sl->link));
+	struct slave_link *sl_new;
+
+	sl_new = alternative_add_slave(a, xstrdup(sl->name), xstrdup(sl->link));
+	sl_new->updated = sl->updated;
 }
 
 static const char *
@@ -1887,9 +1900,10 @@ alternative_has_broken_slave(struct slave_link *sl, struct fileset *fs)
 	return false;
 }
 
-static bool
-alternative_is_broken(struct alternative *a)
+static enum alternative_update_reason
+alternative_needs_update(struct alternative *a)
 {
+	enum alternative_update_reason reason = ALT_UPDATE_NO;
 	const char *current;
 	char *altlnk, *wanted;
 	struct fileset *fs;
@@ -1898,12 +1912,12 @@ alternative_is_broken(struct alternative *a)
 	/* Check master link */
 	altlnk = areadlink(a->master_link);
 	if (!altlnk)
-		return true;
+		return ALT_UPDATE_LINK_BROKEN;
 	xasprintf(&wanted, "%s/%s", altdir, a->master_name);
 	if (strcmp(altlnk, wanted) != 0) {
 		free(wanted);
 		free(altlnk);
-		return true;
+		return ALT_UPDATE_LINK_BROKEN;
 	}
 	free(wanted);
 	free(altlnk);
@@ -1911,20 +1925,24 @@ alternative_is_broken(struct alternative *a)
 	/* Stop if we have an unmanaged alternative */
 	current = alternative_get_current(a);
 	if (current == NULL)
-		return true;
+		return ALT_UPDATE_LINK_BROKEN;
 
 	if (!alternative_has_choice(a, current))
-		return false;
+		return ALT_UPDATE_NO;
 
 	fs = alternative_get_fileset(a, current);
 
 	/* Check slaves */
 	for (sl = a->slaves; sl; sl = sl->next) {
-		if (alternative_has_broken_slave(sl, fs))
-			return true;
+		if (alternative_has_broken_slave(sl, fs)) {
+			if (sl->updated)
+				reason = ALT_UPDATE_SLAVE_CHANGED;
+			else
+				return ALT_UPDATE_LINK_BROKEN;
+		}
 	}
 
-	return false;
+	return reason;
 }
 
 struct alternative_map {
@@ -2253,6 +2271,8 @@ alternative_evolve_slave(struct alternative *a, const char *cur_choice,
 		} else {
 			checked_rm(old);
 		}
+
+		sl->updated = true;
 	}
 	free(new_file);
 }
@@ -2277,6 +2297,9 @@ alternative_evolve(struct alternative *a, struct alternative *b,
 	for (sl = b->slaves; sl; sl = sl->next) {
 		if (alternative_has_slave(a, sl->name))
 			alternative_evolve_slave(a, cur_choice, sl, fs);
+		else
+			sl->updated = true;
+
 		alternative_copy_slave(a, sl);
 	}
 }
@@ -2285,6 +2308,8 @@ static void
 alternative_update(struct alternative *a,
                    const char *current_choice, const char *new_choice)
 {
+	enum alternative_update_reason reason;
+
 	/* No choice left, remove everything. */
 	if (!alternative_choices_count(a)) {
 		log_msg("link group %s fully removed", a->master_name);
@@ -2303,11 +2328,19 @@ alternative_update(struct alternative *a,
 		                                  _("manual mode"));
 		debug("prepare_install(%s)", new_choice);
 		alternative_prepare_install(a, new_choice);
-	} else if (alternative_is_broken(a)) {
-		log_msg("auto-repair link group %s", a->master_name);
-		warning(_("forcing reinstallation of alternative %s because "
-		          "link group %s is broken"), current_choice,
-		        a->master_name);
+	} else if ((reason = alternative_needs_update(a))) {
+		if (reason == ALT_UPDATE_SLAVE_CHANGED) {
+			log_msg("link group %s updated with changed slaves",
+			        a->master_name);
+			info(_("updating alternative %s "
+			       "because link group %s has changed slave links"),
+			     current_choice, a->master_name);
+		} else {
+			log_msg("auto-repair link group %s", a->master_name);
+			warning(_("forcing reinstallation of alternative %s "
+			          "because link group %s is broken"),
+			        current_choice, a->master_name);
+		}
 
 		if (current_choice && !alternative_has_choice(a, current_choice)) {
 			struct fileset *best = alternative_get_best(a);