1 files changed, 113 insertions, 0 deletions
diff --git a/pkg/sentry/fs/host/socket_iovec.go b/pkg/sentry/fs/host/socket_iovec.go
new file mode 100644
index 000000000..1a9587b90
--- /dev/null
+++ b/pkg/sentry/fs/host/socket_iovec.go
@@ -0,0 +1,113 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package host
+
+import (
+	"syscall"
+
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+)
+
+// maxIovs is the maximum number of iovecs to pass to the host.
+var maxIovs = linux.UIO_MAXIOV
+
+// copyToMulti copies as many bytes from src to dst as possible.
+func copyToMulti(dst [][]byte, src []byte) {
+	for _, d := range dst {
+		done := copy(d, src)
+		src = src[done:]
+		if len(src) == 0 {
+			break
+		}
+	}
+}
+
+// copyFromMulti copies as many bytes from src to dst as possible.
+func copyFromMulti(dst []byte, src [][]byte) {
+	for _, s := range src {
+		done := copy(dst, s)
+		dst = dst[done:]
+		if len(dst) == 0 {
+			break
+		}
+	}
+}
+
+// buildIovec builds an iovec slice from the given []byte slice.
+//
+// If truncate, truncate bufs > maxlen. Otherwise, immediately return an error.
+//
+// If length < the total length of bufs, err indicates why, even when returning
+// a truncated iovec.
+//
+// If intermediate != nil, iovecs references intermediate rather than bufs and
+// the caller must copy to/from bufs as necessary.
+func buildIovec(bufs [][]byte, maxlen int, truncate bool) (length uintptr, iovecs []syscall.Iovec, intermediate []byte, err error) {
+	var iovsRequired int
+	for _, b := range bufs {
+		length += uintptr(len(b))
+		if len(b) > 0 {
+			iovsRequired++
+		}
+	}
+
+	stopLen := length
+	if length > uintptr(maxlen) {
+		if truncate {
+			stopLen = uintptr(maxlen)
+			err = syserror.EAGAIN
+		} else {
+			return 0, nil, nil, syserror.EMSGSIZE
+		}
+	}
+
+	if iovsRequired > maxIovs {
+		// The kernel will reject our call if we pass this many iovs.
+		// Use a single intermediate buffer instead.
+		b := make([]byte, stopLen)
+
+		return stopLen, []syscall.Iovec{{
+			Base: &b[0],
+			Len:  uint64(stopLen),
+		}}, b, err
+	}
+
+	var total uintptr
+	iovecs = make([]syscall.Iovec, 0, iovsRequired)
+	for i := range bufs {
+		l := len(bufs[i])
+		if l == 0 {
+			continue
+		}
+
+		stop := l
+		if total+uintptr(stop) > stopLen {
+			stop = int(stopLen - total)
+		}
+
+		iovecs = append(iovecs, syscall.Iovec{
+			Base: &bufs[i][0],
+			Len:  uint64(stop),
+		})
+
+		total += uintptr(stop)
+		if total >= stopLen {
+			break
+		}
+	}
+
+	return total, iovecs, nil, err
+}