Fix the broken AppleDOS double-sided disks. Allow access to side 1 on AppleDOS

volumes.

doc/disk-apple2.md

@@ -46,9 +46,9 @@ fluxengine ls appleii140 --appledos -f image.flux
 In addition, some third-party systems use 80-track double sides drives, with
 the same underlying disk format. These are supported with the `appleii640`
 profile. The complication here is that the AppleDOS filesystem only supports up
-to 50 tracks, so it needs tweaking to support larger disks. FluxEngine doesn't
-understand these tweaks yet but they only become important when writing to
-disks, which isn't supported yet.
+to 50 tracks, so it needs tweaking to support larger disks. It treats the
+second side of the disk as a completely different volume. To access these
+files, use `--appledos --side1`.
 
 [^1]: CP/M disks use the ProDOS translation for the first three tracks and a
     different translation for all the tracks thereafter.

lib/vfs/appledos.cc

@@ -103,7 +103,7 @@ public:
         ByteWriter bw(bytes);
         while (tstrack)
         {
-            Bytes ts = getLogicalSector(tstrack * 16 + tssector);
+            Bytes ts = getAppleSector(tstrack * 16 + tssector);
             ByteReader br(ts);
             br.seek(0x0c);
 
@@ -114,7 +114,7 @@ public:
                 if (!track)
                     goto done;
 
-                bw += getLogicalSector(track * 16 + sector);
+                bw += getAppleSector(track * 16 + sector);
             }
 
             tstrack = ts[1];
@@ -128,7 +128,7 @@ public:
 private:
     void mount()
     {
-        _vtoc = getLogicalSector(VTOC_BLOCK);
+        _vtoc = getAppleSector(VTOC_BLOCK);
         if ((_vtoc[0x27] != 122) || (_vtoc[0x36] != 0) || (_vtoc[0x37] != 1))
             throw BadFilesystemException();
 
@@ -137,7 +137,7 @@ private:
         int sector = _vtoc[2];
         while (track)
         {
-            Bytes dir = getLogicalSector(track * 16 + sector);
+            Bytes dir = getAppleSector(track * 16 + sector);
             ByteReader br(dir);
             br.seek(0x0b);
 
@@ -162,6 +162,12 @@ private:
         throw FileNotFoundException();
     }
 
+    Bytes getAppleSector(uint32_t number, uint32_t count = 1)
+    {
+        return getLogicalSector(
+            number + _config.filesystem_offset_sectors(), count);
+    }
+
 private:
     const AppledosProto& _config;
     Bytes _vtoc;

lib/vfs/vfs.proto

@@ -59,7 +59,12 @@ message CbmfsProto
 
 message ProdosProto {}
 
-message AppledosProto {}
+message AppledosProto {
+	optional uint32 filesystem_offset_sectors = 1 [
+		default = 0,
+		(help) = "offset the entire offset up the disk this many sectors"
+	];
+}
 
 message Smaky6FsProto {}
 

src/formats/appleii640.textpb

@@ -24,17 +24,19 @@ layout {
 	}
 }
 
-decoder {
-	apple2 {
-		side_one_track_offset: 80
-	}
-}
-
-encoder {
-	apple2 {
-		side_one_track_offset: 80
-	}
-}
-
 tpi: 96
 
+option {
+	name: "side1"
+	comment: "reads the volume on side 1 of a disk"
+	message: "accessing volume on side 1"
+
+	config {
+		filesystem {
+			appledos {
+				filesystem_offset_sectors: 0x500
+			}
+		}
+	}
+}
+