1 files changed, 56 insertions, 0 deletions
diff --git a/pkg/sentry/strace/select.go b/pkg/sentry/strace/select.go
new file mode 100644
index 000000000..c77d418e6
--- /dev/null
+++ b/pkg/sentry/strace/select.go
@@ -0,0 +1,56 @@
+// Copyright 2019 The gVisor Authors.
+//
+// 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 strace
+
+import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/syscalls/linux"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
+)
+
+func fdsFromSet(t *kernel.Task, set []byte) []int {
+	var fds []int
+	// Append n if the n-th bit is 1.
+	for i, v := range set {
+		for j := 0; j < 8; j++ {
+			if (v>>j)&1 == 1 {
+				fds = append(fds, i*8+j)
+			}
+		}
+	}
+	return fds
+}
+
+func fdSet(t *kernel.Task, nfds int, addr usermem.Addr) string {
+	if nfds < 0 {
+		return fmt.Sprintf("%#x (negative nfds)", addr)
+	}
+	if addr == 0 {
+		return "null"
+	}
+
+	// Calculate the size of the fd set (one bit per fd).
+	nBytes := (nfds + 7) / 8
+	nBitsInLastPartialByte := nfds % 8
+
+	set, err := linux.CopyInFDSet(t, addr, nBytes, nBitsInLastPartialByte)
+	if err != nil {
+		return fmt.Sprintf("%#x (error decoding fdset: %s)", addr, err)
+	}
+
+	return fmt.Sprintf("%#x %v", addr, fdsFromSet(t, set))
+}