Port readahead to VFS2.

It preserves the same functionality (almost none) as in VFS1.

Updates #2923 #1035

PiperOrigin-RevId: 317943522

2 files changed, 34 insertions, 1 deletions

diff --git a/pkg/sentry/syscalls/linux/vfs2/read_write.go b/pkg/sentry/syscalls/linux/vfs2/read_write.go
index 7f9debd4a..cd25597a7 100644
--- a/pkg/sentry/syscalls/linux/vfs2/read_write.go
+++ b/pkg/sentry/syscalls/linux/vfs2/read_write.go
@@ -606,3 +606,36 @@ func Lseek(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall
 	newoff, err := file.Seek(t, offset, whence)
 	return uintptr(newoff), nil, err
 }
+
+// Readahead implements readahead(2).
+func Readahead(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	fd := args[0].Int()
+	offset := args[1].Int64()
+	size := args[2].SizeT()
+
+	file := t.GetFileVFS2(fd)
+	if file == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer file.DecRef()
+
+	// Check that the file is readable.
+	if !file.IsReadable() {
+		return 0, nil, syserror.EBADF
+	}
+
+	// Check that the size is valid.
+	if int(size) < 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Check that the offset is legitimate and does not overflow.
+	if offset < 0 || offset+int64(size) < 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Return EINVAL; if the underlying file type does not support readahead,
+	// then Linux will return EINVAL to indicate as much. In the future, we
+	// may extend this function to actually support readahead hints.
+	return 0, nil, syserror.EINVAL
+}
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2.go b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
index b463edf2a..9e60c4a1c 100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
@@ -92,7 +92,7 @@ func Override() {
 	s.Table[162] = syscalls.Supported("sync", Sync)
 	s.Table[165] = syscalls.Supported("mount", Mount)
 	s.Table[166] = syscalls.Supported("umount2", Umount2)
-	delete(s.Table, 187) // readahead
+	s.Table[187] = syscalls.Supported("readahead", Readahead)
 	s.Table[188] = syscalls.Supported("setxattr", Setxattr)
 	s.Table[189] = syscalls.Supported("lsetxattr", Lsetxattr)
 	s.Table[190] = syscalls.Supported("fsetxattr", Fsetxattr)