2 files changed, 41 insertions, 0 deletions
diff --git a/pkg/safemem/seq_test.go b/pkg/safemem/seq_test.go
index eba4bb535..de34005e9 100644
--- a/pkg/safemem/seq_test.go
+++ b/pkg/safemem/seq_test.go
@@ -20,6 +20,27 @@ import (
 	"testing"
 )
 
+func TestBlockSeqOfEmptyBlock(t *testing.T) {
+	bs := BlockSeqOf(Block{})
+	if !bs.IsEmpty() {
+		t.Errorf("BlockSeqOf(Block{}).IsEmpty(): got false, wanted true; BlockSeq is %v", bs)
+	}
+}
+
+func TestBlockSeqOfNonemptyBlock(t *testing.T) {
+	b := BlockFromSafeSlice(make([]byte, 1))
+	bs := BlockSeqOf(b)
+	if bs.IsEmpty() {
+		t.Fatalf("BlockSeqOf(non-empty Block).IsEmpty(): got true, wanted false; BlockSeq is %v", bs)
+	}
+	if head := bs.Head(); head != b {
+		t.Fatalf("BlockSeqOf(non-empty Block).Head(): got %v, wanted %v", head, b)
+	}
+	if tail := bs.Tail(); !tail.IsEmpty() {
+		t.Fatalf("BlockSeqOf(non-empty Block).Tail().IsEmpty(): got false, wanted true: tail is %v", tail)
+	}
+}
+
 type blockSeqTest struct {
 	desc string
 
diff --git a/pkg/safemem/seq_unsafe.go b/pkg/safemem/seq_unsafe.go
index 354a95dde..f5f0574f8 100644
--- a/pkg/safemem/seq_unsafe.go
+++ b/pkg/safemem/seq_unsafe.go
@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"fmt"
 	"reflect"
+	"syscall"
 	"unsafe"
 )
 
@@ -55,6 +56,9 @@ type BlockSeq struct {
 
 // BlockSeqOf returns a BlockSeq representing the single Block b.
 func BlockSeqOf(b Block) BlockSeq {
+	if b.length == 0 {
+		return BlockSeq{}
+	}
 	bs := BlockSeq{
 		data:   b.start,
 		length: -1,
@@ -297,3 +301,19 @@ func ZeroSeq(dsts BlockSeq) (uint64, error) {
 	}
 	return done, nil
 }
+
+// IovecsFromBlockSeq returns a []syscall.Iovec representing seq.
+func IovecsFromBlockSeq(bs BlockSeq) []syscall.Iovec {
+	iovs := make([]syscall.Iovec, 0, bs.NumBlocks())
+	for ; !bs.IsEmpty(); bs = bs.Tail() {
+		b := bs.Head()
+		iovs = append(iovs, syscall.Iovec{
+			Base: &b.ToSlice()[0],
+			Len:  uint64(b.Len()),
+		})
+		// We don't need to care about b.NeedSafecopy(), because the host
+		// kernel will handle such address ranges just fine (by returning
+		// EFAULT).
+	}
+	return iovs
+}