ext: Migrate from using fileReader custom interface to using io.Reader.

It gets rid of holding state of the io.Reader offset (which is anyways held by
the vfs.FileDescriptor struct. It is also odd using a io.Reader becuase we
using io.ReaderAt to interact with the device. So making a io.ReaderAt wrapper
makes more sense.

Most importantly, it gets rid of the complexity of extracting the file reader
from a regular file implementation and then using it. Now we can just use the
regular file implementation as a reader which is more intuitive.

PiperOrigin-RevId: 260846927

1 files changed, 16 insertions, 8 deletions

diff --git a/pkg/sentry/fs/ext/inode.go b/pkg/sentry/fs/ext/inode.go
index 00e022953..364980e4c 100644
--- a/pkg/sentry/fs/ext/inode.go
+++ b/pkg/sentry/fs/ext/inode.go
@@ -46,6 +46,12 @@ type inode struct {
 	// identify inodes within the ext filesystem.
 	inodeNum uint32
 
+	// dev represents the underlying device. Same as filesystem.dev.
+	dev io.ReaderAt
+
+	// blkSize is the fs data block size. Same as filesystem.sb.BlockSize().
+	blkSize uint64
+
 	// diskInode gives us access to the inode struct on disk. Immutable.
 	diskInode disklayout.Inode
 
@@ -86,12 +92,12 @@ func (in *inode) decRef(fs *filesystem) {
 
 // newInode is the inode constructor. Reads the inode off disk. Identifies
 // inodes based on the absolute inode number on disk.
-func newInode(ctx context.Context, dev io.ReaderAt, sb disklayout.SuperBlock, bgs []disklayout.BlockGroup, inodeNum uint32) (*inode, error) {
+func newInode(ctx context.Context, fs *filesystem, inodeNum uint32) (*inode, error) {
 	if inodeNum == 0 {
 		panic("inode number 0 on ext filesystems is not possible")
 	}
 
-	inodeRecordSize := sb.InodeSize()
+	inodeRecordSize := fs.sb.InodeSize()
 	var diskInode disklayout.Inode
 	if inodeRecordSize == disklayout.OldInodeSize {
 		diskInode = &disklayout.InodeOld{}
@@ -100,12 +106,12 @@ func newInode(ctx context.Context, dev io.ReaderAt, sb disklayout.SuperBlock, bg
 	}
 
 	// Calculate where the inode is actually placed.
-	inodesPerGrp := sb.InodesPerGroup()
-	blkSize := sb.BlockSize()
-	inodeTableOff := bgs[getBGNum(inodeNum, inodesPerGrp)].InodeTable() * blkSize
+	inodesPerGrp := fs.sb.InodesPerGroup()
+	blkSize := fs.sb.BlockSize()
+	inodeTableOff := fs.bgs[getBGNum(inodeNum, inodesPerGrp)].InodeTable() * blkSize
 	inodeOff := inodeTableOff + uint64(uint32(inodeRecordSize)*getBGOff(inodeNum, inodesPerGrp))
 
-	if err := readFromDisk(dev, int64(inodeOff), diskInode); err != nil {
+	if err := readFromDisk(fs.dev, int64(inodeOff), diskInode); err != nil {
 		return nil, err
 	}
 
@@ -113,18 +119,20 @@ func newInode(ctx context.Context, dev io.ReaderAt, sb disklayout.SuperBlock, bg
 	inode := inode{
 		refs:      1,
 		inodeNum:  inodeNum,
+		dev:       fs.dev,
+		blkSize:   blkSize,
 		diskInode: diskInode,
 	}
 
 	switch diskInode.Mode().FileType() {
 	case linux.ModeSymlink:
-		f, err := newSymlink(dev, blkSize, inode)
+		f, err := newSymlink(inode)
 		if err != nil {
 			return nil, err
 		}
 		return &f.inode, nil
 	case linux.ModeRegular:
-		f, err := newRegularFile(dev, blkSize, inode)
+		f, err := newRegularFile(inode)
 		if err != nil {
 			return nil, err
 		}