2 files changed, 244 insertions, 0 deletions
diff --git a/cmd/ioworkload/scenario_retbytes.go b/cmd/ioworkload/scenario_retbytes.go
new file mode 100644
index 0000000..fa0b677
--- /dev/null
+++ b/cmd/ioworkload/scenario_retbytes.go
@@ -0,0 +1,243 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"syscall"
+	"unsafe"
+)
+
+const (
+	sysProcessVMReadv  = 310
+	sysProcessVMWritev = 311
+	retbytesPayloadLen = 18
+)
+
+// retbytesPhaseA exercises byte-classified syscalls that use generic ret_event exits.
+func retbytesPhaseA() error {
+	if err := retbytesSocketIO(); err != nil {
+		return err
+	}
+	if err := retbytesSendfile(); err != nil {
+		return err
+	}
+	if err := retbytesSplice(); err != nil {
+		return err
+	}
+	if err := retbytesTee(); err != nil {
+		return err
+	}
+	return retbytesProcessVM()
+}
+
+func retbytesSocketIO() error {
+	fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		return fmt.Errorf("socketpair: %w", err)
+	}
+	defer syscall.Close(fds[0])
+	defer syscall.Close(fds[1])
+
+	payload := []byte("phase-a-send-recv!")
+	if err := syscall.Sendto(fds[0], payload, 0, nil); err != nil {
+		return fmt.Errorf("sendto: %w", err)
+	}
+	buf := make([]byte, len(payload))
+	n, _, err := syscall.Recvfrom(fds[1], buf, 0)
+	if err != nil {
+		return fmt.Errorf("recvfrom: %w", err)
+	}
+	if n != len(payload) {
+		return fmt.Errorf("recvfrom read %d bytes, want %d", n, len(payload))
+	}
+
+	if n, err := syscall.SendmsgN(fds[0], payload, nil, nil, 0); err != nil {
+		return fmt.Errorf("sendmsg: %w", err)
+	} else if n != len(payload) {
+		return fmt.Errorf("sendmsg wrote %d bytes, want %d", n, len(payload))
+	}
+	n, _, _, _, err = syscall.Recvmsg(fds[1], buf, nil, 0)
+	if err != nil {
+		return fmt.Errorf("recvmsg: %w", err)
+	}
+	if n != len(payload) {
+		return fmt.Errorf("recvmsg read %d bytes, want %d", n, len(payload))
+	}
+	return nil
+}
+
+func retbytesSendfile() error {
+	dir, cleanup, err := makeTempDir("retbytes-sendfile")
+	if err != nil {
+		return err
+	}
+	defer cleanup()
+
+	src, dst, err := openTransferFiles(dir, "sendfilesrc.txt", "sendfiledst.txt")
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(src)
+	defer syscall.Close(dst)
+
+	n, err := syscall.Sendfile(dst, src, nil, retbytesPayloadLen)
+	if err != nil {
+		return fmt.Errorf("sendfile: %w", err)
+	}
+	if n != retbytesPayloadLen {
+		return fmt.Errorf("sendfile copied %d bytes, want %d", n, retbytesPayloadLen)
+	}
+	return nil
+}
+
+func retbytesSplice() error {
+	dir, cleanup, err := makeTempDir("retbytes-splice")
+	if err != nil {
+		return err
+	}
+	defer cleanup()
+
+	src, err := openPayloadFile(filepath.Join(dir, "splicesrc.txt"))
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(src)
+
+	pipe := make([]int, 2)
+	if err := syscall.Pipe2(pipe, syscall.O_CLOEXEC); err != nil {
+		return fmt.Errorf("pipe2: %w", err)
+	}
+	defer syscall.Close(pipe[0])
+	defer syscall.Close(pipe[1])
+
+	n, err := syscall.Splice(src, nil, pipe[1], nil, retbytesPayloadLen, 0)
+	if err != nil {
+		return fmt.Errorf("splice: %w", err)
+	}
+	if n != retbytesPayloadLen {
+		return fmt.Errorf("splice copied %d bytes, want %d", n, retbytesPayloadLen)
+	}
+	return nil
+}
+
+func retbytesTee() error {
+	pipeA := make([]int, 2)
+	if err := syscall.Pipe2(pipeA, syscall.O_CLOEXEC); err != nil {
+		return fmt.Errorf("pipe2 source: %w", err)
+	}
+	defer syscall.Close(pipeA[0])
+	defer syscall.Close(pipeA[1])
+
+	pipeB := make([]int, 2)
+	if err := syscall.Pipe2(pipeB, syscall.O_CLOEXEC); err != nil {
+		return fmt.Errorf("pipe2 dest: %w", err)
+	}
+	defer syscall.Close(pipeB[0])
+	defer syscall.Close(pipeB[1])
+
+	payload := []byte("phase-a-tee-bytes!")
+	if _, err := syscall.Write(pipeA[1], payload); err != nil {
+		return fmt.Errorf("write pipe: %w", err)
+	}
+	n, err := syscall.Tee(pipeA[0], pipeB[1], len(payload), 0)
+	if err != nil {
+		return fmt.Errorf("tee: %w", err)
+	}
+	if n != int64(len(payload)) {
+		return fmt.Errorf("tee copied %d bytes, want %d", n, len(payload))
+	}
+	return nil
+}
+
+func retbytesProcessVM() error {
+	src := []byte("phase-a-process-vm")
+	dst := make([]byte, len(src))
+	if n, err := processVMWritev(os.Getpid(), dst, src); err != nil {
+		return err
+	} else if n != len(src) {
+		return fmt.Errorf("process_vm_writev wrote %d bytes, want %d", n, len(src))
+	}
+
+	readBuf := make([]byte, len(dst))
+	if n, err := processVMReadv(os.Getpid(), readBuf, dst); err != nil {
+		return err
+	} else if n != len(dst) {
+		return fmt.Errorf("process_vm_readv read %d bytes, want %d", n, len(dst))
+	}
+	runtime.KeepAlive(src)
+	runtime.KeepAlive(dst)
+	runtime.KeepAlive(readBuf)
+	return nil
+}
+
+func openTransferFiles(dir, srcName, dstName string) (int, int, error) {
+	src, err := openPayloadFile(filepath.Join(dir, srcName))
+	if err != nil {
+		return 0, 0, err
+	}
+	dstPath := filepath.Join(dir, dstName)
+	dst, err := syscall.Open(dstPath, syscall.O_RDWR|syscall.O_CREAT|syscall.O_TRUNC, 0o644)
+	if err != nil {
+		syscall.Close(src)
+		return 0, 0, fmt.Errorf("open destination: %w", err)
+	}
+	return src, dst, nil
+}
+
+func openPayloadFile(path string) (int, error) {
+	fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT|syscall.O_TRUNC, 0o644)
+	if err != nil {
+		return 0, fmt.Errorf("open payload: %w", err)
+	}
+	if _, err := syscall.Write(fd, []byte("phase-a-ret-bytes!")); err != nil {
+		syscall.Close(fd)
+		return 0, fmt.Errorf("write payload: %w", err)
+	}
+	if _, err := syscall.Seek(fd, 0, 0); err != nil {
+		syscall.Close(fd)
+		return 0, fmt.Errorf("seek payload: %w", err)
+	}
+	return fd, nil
+}
+
+func processVMReadv(pid int, local, remote []byte) (int, error) {
+	localIov := syscall.Iovec{Base: &local[0], Len: uint64(len(local))}
+	remoteIov := syscall.Iovec{Base: &remote[0], Len: uint64(len(remote))}
+	n, _, errno := syscall.Syscall6(
+		sysProcessVMReadv,
+		uintptr(pid),
+		uintptr(unsafe.Pointer(&localIov)),
+		1,
+		uintptr(unsafe.Pointer(&remoteIov)),
+		1,
+		0,
+	)
+	runtime.KeepAlive(local)
+	runtime.KeepAlive(remote)
+	if errno != 0 {
+		return 0, fmt.Errorf("process_vm_readv: %w", errno)
+	}
+	return int(n), nil
+}
+
+func processVMWritev(pid int, remote, local []byte) (int, error) {
+	localIov := syscall.Iovec{Base: &local[0], Len: uint64(len(local))}
+	remoteIov := syscall.Iovec{Base: &remote[0], Len: uint64(len(remote))}
+	n, _, errno := syscall.Syscall6(
+		sysProcessVMWritev,
+		uintptr(pid),
+		uintptr(unsafe.Pointer(&localIov)),
+		1,
+		uintptr(unsafe.Pointer(&remoteIov)),
+		1,
+		0,
+	)
+	runtime.KeepAlive(local)
+	runtime.KeepAlive(remote)
+	if errno != 0 {
+		return 0, fmt.Errorf("process_vm_writev: %w", errno)
+	}
+	return int(n), nil
+}
diff --git a/cmd/ioworkload/scenarios.go b/cmd/ioworkload/scenarios.go
index 6910314..fc06825 100644
--- a/cmd/ioworkload/scenarios.go
+++ b/cmd/ioworkload/scenarios.go
@@ -24,6 +24,7 @@ var scenarios = map[string]func() error{
 	"readwrite-rdonly-write":      readwriteRdonlyWrite,
 	"readwrite-pread-invalid":     readwritePreadInvalid,
 	"readwrite-pwrite-invalid":    readwritePwriteInvalid,
+	"retbytes-phase-a":            retbytesPhaseA,
 	"close-basic":                 closeBasic,
 	"close-range":                 closeRange,
 	"close-invalid-fd":            closeInvalidFd,