Add initial ext2 read/write and formatting support

Register ext2 at boot, integrate mode-aware VFS opens and volume cleanup, and queue asynchronous transfers through a persistent worker.

Validation: Pascal compiler check and git diff --check passed. Full build blocked by Docker engine HTTP 500; runtime and Linux interoperability remain unverified.

src/boot/boot.mgr.pas

@@ -96,6 +96,7 @@ uses
     driver.net.dev.e1000,
     driver.bus.usb.ehci,
     driver.storage.fs.fat32,
+    driver.storage.fs.ext2,
     arch.x86.fault,
     core.ds.fifo,
     driver.storage.fs.mgr,

src/driver/storage/driver.storage.types.pas

@@ -222,6 +222,8 @@ type
       to read/write hooks.  Also returns the current file size through the
       var parameter.  Returning nil is legal (disables per-call fast-path). }
     PPOpenFileHook = function(volume : PStorage_Volume; directory : pchar; fileName : pchar; var fileSize : uint32) : pointer;
+    { Mode-aware open avoids creating a missing file during a read-only open. }
+    PPOpenFileModeHook = function(volume : PStorage_Volume; directory : pchar; fileName : pchar; allowCreate : boolean; var fileSize : uint32) : pointer;
     { Per-file close hook: frees the context allocated by openFileCallback. }
     PPCloseFileHook = procedure(ctx : pointer);
 
@@ -324,6 +326,7 @@ type
         renameFileCallback      : PPRenameFileHook;
         { Per-file open/close — nil if FS does not cache per-file metadata }
         openFileCallback        : PPOpenFileHook;
+        openFileModeCallback    : PPOpenFileModeHook;
         closeFileCallback       : PPCloseFileHook;
         formatParamFlags        : uint32;
         validateLabelCallback   : PPValidateLabelHook;

src/driver/storage/driver.storage.vfs.pas

@@ -152,6 +152,7 @@ implementation
 uses
     driver.storage.fs.mgr,
     driver.storage.fs.fat32,
+    driver.storage.fs.ext2,
     proc.mgr,
     proc.types,
     io.stdio,
@@ -618,6 +619,8 @@ begin
 
     if (vol^.filesystem <> nil) and (stringCompare(vol^.filesystem^.sName, 'FAT32') = 0) then
         FAT32ReleaseVolumeState(vol);
+    if (vol^.filesystem <> nil) and (stringCompare(vol^.filesystem^.sName, 'EXT2') = 0) then
+        driver.storage.fs.ext2.ReleaseVolume(vol);
 
     InvalidateVolume := true;
     debug.tracer.push_trace('driver.storage.vfs.InvalidateVolume.exit');
@@ -1427,8 +1430,12 @@ begin
     fd^.FSCloseHook := nil;
 
     { Cache per-file metadata and populate DataSize via FS open hook }
-    if (vol^.filesystem <> nil) and (vol^.filesystem^.openFileCallback <> nil) then begin
-        fd^.FSPrivate := vol^.filesystem^.openFileCallback(vol, dir, fname, fd^.DataSize);
+    if (vol^.filesystem <> nil) and ((vol^.filesystem^.openFileCallback <> nil) or
+       (vol^.filesystem^.openFileModeCallback <> nil)) then begin
+        if vol^.filesystem^.openFileModeCallback <> nil then
+            fd^.FSPrivate := vol^.filesystem^.openFileModeCallback(vol, dir, fname,
+                (OpenMode = omCreate) or (OpenMode = omWrite), fd^.DataSize)
+        else fd^.FSPrivate := vol^.filesystem^.openFileCallback(vol, dir, fname, fd^.DataSize);
         if fd^.FSPrivate = nil then begin
             if Error <> nil then begin
                 if (OpenMode = omCreate) or (OpenMode = omWrite) then
@@ -1724,8 +1731,12 @@ begin
     fd^.FSCloseHook := nil;
     OutHandle := slot;
 
-    if (vol^.filesystem <> nil) and (vol^.filesystem^.openFileCallback <> nil) then begin
-        fd^.FSPrivate := vol^.filesystem^.openFileCallback(vol, dir, fname, fd^.DataSize);
+    if (vol^.filesystem <> nil) and ((vol^.filesystem^.openFileCallback <> nil) or
+       (vol^.filesystem^.openFileModeCallback <> nil)) then begin
+        if vol^.filesystem^.openFileModeCallback <> nil then
+            fd^.FSPrivate := vol^.filesystem^.openFileModeCallback(vol, dir, fname,
+                (OpenMode = omCreate) or (OpenMode = omWrite), fd^.DataSize)
+        else fd^.FSPrivate := vol^.filesystem^.openFileCallback(vol, dir, fname, fd^.DataSize);
         if fd^.FSPrivate = nil then begin
             if Error <> nil then begin
                 if (OpenMode = omCreate) or (OpenMode = omWrite) then

src/driver/storage/fs/ext2/driver.storage.fs.ext2.types.pas

@@ -0,0 +1,62 @@
+unit driver.storage.fs.ext2.types;
+
+interface
+uses driver.storage.types;
+
+const
+    EXT2_MAGIC = $EF53;
+    EXT2_DIR = $4000;
+    EXT2_FILE = $8000;
+    EXT2_ROOT = 2;
+
+type
+    TExt2Inode = packed record
+        Mode, UID : uint16;
+        Size, ATime, CTime, MTime, DTime : uint32;
+        GID, Links : uint16;
+        Sectors, Flags, OSData : uint32;
+        Blocks : array[0..14] of uint32;
+        Generation, ACL, SizeHigh, Fragment : uint32;
+        OSExtra : array[0..11] of uint8;
+    end;
+    PExt2Inode = ^TExt2Inode;
+    TExt2Group = packed record
+        BlockBitmap, InodeBitmap, InodeTable : uint32;
+        FreeBlocks, FreeInodes, Directories, Pad : uint16;
+        Reserved : array[0..2] of uint32;
+    end;
+    PExt2Group = ^TExt2Group;
+    TExt2Dirent = packed record
+        Inode : uint32;
+        Length : uint16;
+        NameLength, FileType : uint8;
+    end;
+    PExt2Dirent = ^TExt2Dirent;
+    PExt2Volume = ^TExt2Volume;
+    PExt2File = ^TExt2File;
+    TExt2Volume = record
+        Volume : PStorage_Volume;
+        Super, Groups : puint8;
+        BlockSize, SectorsPerBlock, BlockCount, InodeCount : uint32;
+        FirstBlock, BlocksPerGroup, InodesPerGroup, InodeSize : uint32;
+        GroupCount, GDTBlocks, AllocGroup : uint32;
+        Busy, Writable, Poisoned, FileTypes : boolean;
+        Files : PExt2File;
+    end;
+    TExt2File = record
+        Volume : PExt2Volume;
+        Inode : uint32;
+        Next : PExt2File;
+    end;
+    { One operation owns its buffers. No DMA destination is shared with another
+      operation. The volume lock protects metadata and all read/modify/write. }
+    TExt2Op = record
+        V : PExt2Volume;
+        Scratch, Data : puint8;
+        Error : TError;
+        Mutating : boolean;
+    end;
+    PExt2Op = ^TExt2Op;
+
+implementation
+end.