Fix lsinfo and add for mounted databases.

If `SimpleDatabase::Visit` is called on a database that contains a mounted directry the URIs of the elements passed to the callbacks are not prefixed by the mountpoint path. This leads to lsinfo and add not working because they use the wrong URI. This pull request is using the `WalkMount` helper function to create prefixed versions of `VisitDirectory`, `VisitSong` and `VisitPlaylist` to add the correct prefix to the parameters of the callback functions.

src/db/plugins/simple/Directory.cxx

@@ -230,7 +230,7 @@ Directory::Walk(bool recursive, const SongFilter *filter,
 		   call will lock it again */
 		const ScopeDatabaseUnlock unlock;
 		WalkMount(GetPath(), *mounted_database,
-			  recursive, filter,
+			  "", recursive, filter,
 			  visit_directory, visit_song,
 			  visit_playlist);
 		return;

src/db/plugins/simple/Mount.cxx

@@ -72,7 +72,7 @@ PrefixVisitPlaylist(const char *base, const VisitPlaylist &visit_playlist,
 
 void
 WalkMount(const char *base, const Database &db,
-	  bool recursive, const SongFilter *filter,
+	  const char* uri, bool recursive, const SongFilter *filter,
 	  const VisitDirectory &visit_directory, const VisitSong &visit_song,
 	  const VisitPlaylist &visit_playlist)
 {
@@ -93,5 +93,5 @@ WalkMount(const char *base, const Database &db,
 		vp = std::bind(PrefixVisitPlaylist,
 			       base, std::ref(visit_playlist), _1, _2);
 
-	db.Visit(DatabaseSelection("", recursive, filter), vd, vs, vp);
+	db.Visit(DatabaseSelection(uri, recursive, filter), vd, vs, vp);
 }

src/db/plugins/simple/Mount.hxx

@@ -27,7 +27,7 @@ class SongFilter;
 
 void
 WalkMount(const char *base, const Database &db,
-	  bool recursive, const SongFilter *filter,
+	  const char* uri, bool recursive, const SongFilter *filter,
 	  const VisitDirectory &visit_directory, const VisitSong &visit_song,
 	  const VisitPlaylist &visit_playlist);
 

src/db/plugins/simple/SimpleDatabasePlugin.cxx

@@ -20,6 +20,7 @@
 #include "config.h"
 #include "SimpleDatabasePlugin.hxx"
 #include "PrefixedLightSong.hxx"
+#include "Mount.hxx"
 #include "db/DatabasePlugin.hxx"
 #include "db/Selection.hxx"
 #include "db/Helpers.hxx"
@@ -270,6 +271,18 @@ SimpleDatabase::Visit(const DatabaseSelection &selection,
 	ScopeDatabaseLock protect;
 
 	auto r = root->LookupDirectory(selection.uri.c_str());
+
+	if (r.directory->IsMount()) {
+		/* pass the request and the remaining uri to the mounted database */
+		protect.unlock();
+
+		WalkMount(r.directory->GetPath(), *(r.directory->mounted_database),
+			(r.uri == nullptr)?"":r.uri, selection.recursive, selection.filter,
+			visit_directory, visit_song, visit_playlist);
+
+		return;
+	}
+
 	if (r.uri == nullptr) {
 		/* it's a directory */