exfat: use diff structs 4 vol labels and filenames

... and rename the structs to reflect this.

* Volume labels contain up to 11 uint16s (11 2-byte UTF-16 characters).
* Filenames are packed into 1 to 17 structs of 15 uint16s each (for a total
  of 255 2-byte UTF-16 characters).
* Use 2 different packed structs in the exfat_entry union (same bytes, accessed
  with different structs) to access these 2 things.
* Remove a check that assumed the length returned the number of 2-byte UTF-16
  characters, i.e. the number of uint16s the string uses. It doesn't, it
  returns the number of characters contained in the string which might be 2 or
  4-bytes wide. We're doing the conversion wrong for 4-byte UTF-16 characters
  anyway, more on that later.

src/add-ons/kernel/file_systems/exfat/DirectoryIterator.cpp

@@ -208,9 +208,9 @@ DirectoryIterator::_GetNext(uchar* name, size_t* _nameLength, ino_t* _id,
 				visitor->VisitFileInfo(fCurrent);
 		} else if (fCurrent->type == EXFAT_ENTRY_TYPE_FILENAME) {
 			TRACE("DirectoryIterator::_GetNext() Filename\n");
-			memcpy((uint8*)name + nameIndex, fCurrent->label.name,
+			memcpy((uint8*)name + nameIndex, fCurrent->file_name.name,
-				sizeof(fCurrent->label.name));
+				sizeof(fCurrent->file_name.name));
-			nameIndex += sizeof(fCurrent->label.name);
+			nameIndex += sizeof(fCurrent->file_name.name);
 			name[nameIndex] = '\0';
 			chunkCount--;
 			if (visitor != NULL)

src/add-ons/kernel/file_systems/exfat/Utility.cpp

@@ -30,14 +30,9 @@ get_volume_name(struct exfat_entry* entry, char* name, size_t length)
 	if (entry->type == EXFAT_ENTRY_TYPE_NOT_IN_USE)
 		name = "";
 	else if (entry->type == EXFAT_ENTRY_TYPE_LABEL) {
-		// UCS-2 can encode codepoints in the range U+0000 to U+FFFF
+		status_t result
-		// UTF-8 needs at most 3 bytes to encode values in this range
+			= unicode_to_utf8((const uchar*)entry->volume_label.name,
-		size_t utf8NameLength = entry->label.length * 3;
+				entry->volume_label.length * 2, (uint8*)name, &length);
-		if (length < utf8NameLength)
-			return B_NAME_TOO_LONG;
-
-		status_t result = unicode_to_utf8((const uchar*)entry->label.name,
-			entry->label.length * 2, (uint8*)name, &utf8NameLength);
 		if (result != B_OK)
 			return result;
 	} else

src/add-ons/kernel/file_systems/exfat/exfat.h

@@ -104,14 +104,14 @@ struct exfat_entry {
 			uint8 length;
 			uint16 name[11];
 			uint8 reserved[8];
-		} _PACKED label;
+		} _PACKED volume_label;
 		struct {
 			uint8 chunkCount;
 			uint16 checksum;
 			uint16 flags;
 			uint8 guid[16];
 			uint8 reserved[10];
-		} _PACKED guid;
+		} _PACKED volume_guid;
 		struct {
 			uint8 reserved[3];
 			uint32 checksum;
@@ -171,6 +171,10 @@ struct exfat_entry {
 			uint64 Size() const
 				{ return B_LENDIAN_TO_HOST_INT64(size1); }
 		} _PACKED file_info;
+		struct {
+			uint8 flags;
+			uint16 name[15];
+		} _PACKED file_name;
 	};
 } _PACKED;