Remove FileReadWriteSeeker from vfs.

Previous experience has shown that these types of wrappers tends to create two
kinds of problems: hidden allocations (e.g. each call to
FileReadWriteSeeker.Read/Write allocates a usermem.BytesIO on the heap) and
hidden lock ordering problems (e.g. VFS1 splice deadlocks). Since this is only
needed by fsimpl/verity, move it there.

PiperOrigin-RevId: 345377830

2 files changed, 49 insertions, 7 deletions

diff --git a/pkg/sentry/fsimpl/verity/filesystem.go b/pkg/sentry/fsimpl/verity/filesystem.go
index 59fcff498..04e7110a3 100644
--- a/pkg/sentry/fsimpl/verity/filesystem.go
+++ b/pkg/sentry/fsimpl/verity/filesystem.go
@@ -254,7 +254,7 @@ func (fs *filesystem) verifyChildLocked(ctx context.Context, parent *dentry, chi
 		return nil, alertIntegrityViolation(fmt.Sprintf("Failed to convert xattr %s for %s to int: %v", merkleSizeXattr, childPath, err))
 	}
 
-	fdReader := vfs.FileReadWriteSeeker{
+	fdReader := FileReadWriteSeeker{
 		FD:  parentMerkleFD,
 		Ctx: ctx,
 	}
@@ -397,7 +397,7 @@ func (fs *filesystem) verifyStatAndChildrenLocked(ctx context.Context, d *dentry
 		}
 	}
 
-	fdReader := vfs.FileReadWriteSeeker{
+	fdReader := FileReadWriteSeeker{
 		FD:  fd,
 		Ctx: ctx,
 	}
diff --git a/pkg/sentry/fsimpl/verity/verity.go b/pkg/sentry/fsimpl/verity/verity.go
index add65bee6..5788c661f 100644
--- a/pkg/sentry/fsimpl/verity/verity.go
+++ b/pkg/sentry/fsimpl/verity/verity.go
@@ -749,15 +749,15 @@ func (fd *fileDescription) Seek(ctx context.Context, offset int64, whence int32)
 //
 // Preconditions: fd.d.fs.verityMu must be locked.
 func (fd *fileDescription) generateMerkleLocked(ctx context.Context) ([]byte, uint64, error) {
-	fdReader := vfs.FileReadWriteSeeker{
+	fdReader := FileReadWriteSeeker{
 		FD:  fd.lowerFD,
 		Ctx: ctx,
 	}
-	merkleReader := vfs.FileReadWriteSeeker{
+	merkleReader := FileReadWriteSeeker{
 		FD:  fd.merkleReader,
 		Ctx: ctx,
 	}
-	merkleWriter := vfs.FileReadWriteSeeker{
+	merkleWriter := FileReadWriteSeeker{
 		FD:  fd.merkleWriter,
 		Ctx: ctx,
 	}
@@ -1047,12 +1047,12 @@ func (fd *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, of
 		return 0, alertIntegrityViolation(fmt.Sprintf("Failed to convert xattr %s to int: %v", merkleSizeXattr, err))
 	}
 
-	dataReader := vfs.FileReadWriteSeeker{
+	dataReader := FileReadWriteSeeker{
 		FD:  fd.lowerFD,
 		Ctx: ctx,
 	}
 
-	merkleReader := vfs.FileReadWriteSeeker{
+	merkleReader := FileReadWriteSeeker{
 		FD:  fd.merkleReader,
 		Ctx: ctx,
 	}
@@ -1101,3 +1101,45 @@ func (fd *fileDescription) LockPOSIX(ctx context.Context, uid fslock.UniqueID, t
 func (fd *fileDescription) UnlockPOSIX(ctx context.Context, uid fslock.UniqueID, start, length uint64, whence int16) error {
 	return fd.lowerFD.UnlockPOSIX(ctx, uid, start, length, whence)
 }
+
+// FileReadWriteSeeker is a helper struct to pass a vfs.FileDescription as
+// io.Reader/io.Writer/io.ReadSeeker/io.ReaderAt/io.WriterAt/etc.
+type FileReadWriteSeeker struct {
+	FD    *vfs.FileDescription
+	Ctx   context.Context
+	ROpts vfs.ReadOptions
+	WOpts vfs.WriteOptions
+}
+
+// ReadAt implements io.ReaderAt.ReadAt.
+func (f *FileReadWriteSeeker) ReadAt(p []byte, off int64) (int, error) {
+	dst := usermem.BytesIOSequence(p)
+	n, err := f.FD.PRead(f.Ctx, dst, off, f.ROpts)
+	return int(n), err
+}
+
+// Read implements io.ReadWriteSeeker.Read.
+func (f *FileReadWriteSeeker) Read(p []byte) (int, error) {
+	dst := usermem.BytesIOSequence(p)
+	n, err := f.FD.Read(f.Ctx, dst, f.ROpts)
+	return int(n), err
+}
+
+// Seek implements io.ReadWriteSeeker.Seek.
+func (f *FileReadWriteSeeker) Seek(offset int64, whence int) (int64, error) {
+	return f.FD.Seek(f.Ctx, offset, int32(whence))
+}
+
+// WriteAt implements io.WriterAt.WriteAt.
+func (f *FileReadWriteSeeker) WriteAt(p []byte, off int64) (int, error) {
+	dst := usermem.BytesIOSequence(p)
+	n, err := f.FD.PWrite(f.Ctx, dst, off, f.WOpts)
+	return int(n), err
+}
+
+// Write implements io.ReadWriteSeeker.Write.
+func (f *FileReadWriteSeeker) Write(p []byte) (int, error) {
+	buf := usermem.BytesIOSequence(p)
+	n, err := f.FD.Write(f.Ctx, buf, f.WOpts)
+	return int(n), err
+}