Migrate from using io.ReadSeeker to io.ReaderAt.

This provides the following benefits:
- We can now use pkg/fd package which does not take ownership
  of the file descriptor. So it does not close the fd when garbage collected.
  This reduces scope of errors from unexpected garbage collection of io.File.
- It enforces the offset parameter in every read call.
  It does not affect the fd offset nor is it affected by it. Hence reducing
  scope of error of using stale offsets when reading.
- We do not need to serialize the usage of any global file descriptor anymore.
  So this drops the mutual exclusion req hence reducing complexity and
  congestion.

PiperOrigin-RevId: 260635174

1 files changed, 2 insertions, 7 deletions

diff --git a/pkg/sentry/fs/ext/regular_file.go b/pkg/sentry/fs/ext/regular_file.go
index 9bf39acfe..b48f61795 100644
--- a/pkg/sentry/fs/ext/regular_file.go
+++ b/pkg/sentry/fs/ext/regular_file.go
@@ -29,10 +29,7 @@ type fileReader interface {
 	//
 	// This reader is not meant to be retained across Read operations as it needs
 	// to be reinitialized with the correct offset for every Read.
-	//
-	// Precondition: Must hold the mutex of the filesystem containing dev while
-	//               using the Reader.
-	getFileReader(dev io.ReadSeeker, blkSize uint64, offset uint64) io.Reader
+	getFileReader(dev io.ReaderAt, blkSize uint64, offset uint64) io.Reader
 }
 
 // regularFile represents a regular file's inode. This too follows the
@@ -48,9 +45,7 @@ type regularFile struct {
 
 // newRegularFile is the regularFile constructor. It figures out what kind of
 // file this is and initializes the fileReader.
-//
-// Preconditions: Must hold the mutex of the filesystem containing dev.
-func newRegularFile(dev io.ReadSeeker, blkSize uint64, inode inode) (*regularFile, error) {
+func newRegularFile(dev io.ReaderAt, blkSize uint64, inode inode) (*regularFile, error) {
 	regFile := regularFile{
 		inode: inode,
 	}