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, 12 insertions, 23 deletions

diff --git a/pkg/sentry/fs/ext/inline_file.go b/pkg/sentry/fs/ext/inline_file.go
index b9adfe548..67a538ba0 100644
--- a/pkg/sentry/fs/ext/inline_file.go
+++ b/pkg/sentry/fs/ext/inline_file.go
@@ -24,14 +24,8 @@ type inlineFile struct {
 	regFile regularFile
 }
 
-// Compiles only if inlineFile implements fileReader.
-var _ fileReader = (*inlineFile)(nil)
-
-// getFileReader implements fileReader.getFileReader.
-func (f *inlineFile) getFileReader(_ io.ReaderAt, _ uint64, offset uint64) io.Reader {
-	diskInode := f.regFile.inode.diskInode
-	return &inlineReader{offset: offset, data: diskInode.Data()[:diskInode.Size()]}
-}
+// Compiles only if inlineFile implements io.ReaderAt.
+var _ io.ReaderAt = (*inlineFile)(nil)
 
 // newInlineFile is the inlineFile constructor.
 func newInlineFile(regFile regularFile) *inlineFile {
@@ -40,27 +34,22 @@ func newInlineFile(regFile regularFile) *inlineFile {
 	return file
 }
 
-// inlineReader implements io.Reader which can read the underlying data. This
-// is not thread safe.
-type inlineReader struct {
-	offset uint64
-	data   []byte
-}
-
-// Compiles only if inlineReader implements io.Reader.
-var _ io.Reader = (*inlineReader)(nil)
-
-// Read implements io.Reader.Read.
-func (r *inlineReader) Read(dst []byte) (int, error) {
+// ReadAt implements io.ReaderAt.ReadAt.
+func (f *inlineFile) ReadAt(dst []byte, off int64) (int, error) {
 	if len(dst) == 0 {
 		return 0, nil
 	}
 
-	if int(r.offset) >= len(r.data) {
+	size := f.regFile.inode.diskInode.Size()
+	if uint64(off) >= size {
 		return 0, io.EOF
 	}
 
-	n := copy(dst, r.data[r.offset:])
-	r.offset += uint64(n)
+	to := uint64(off) + uint64(len(dst))
+	if to > size {
+		to = size
+	}
+
+	n := copy(dst, f.regFile.inode.diskInode.Data()[off:to])
 	return n, nil
 }