1 files changed, 67 insertions, 0 deletions
diff --git a/pkg/sentry/hostcpu/hostcpu.go b/pkg/sentry/hostcpu/hostcpu.go
new file mode 100644
index 000000000..fa46499ad
--- /dev/null
+++ b/pkg/sentry/hostcpu/hostcpu.go
@@ -0,0 +1,67 @@
+// 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 hostcpu provides utilities for working with CPU information provided
+// by a host Linux kernel.
+package hostcpu
+
+import (
+	"fmt"
+	"io/ioutil"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// GetCPU returns the caller's current CPU number, without using the Linux VDSO
+// (which is not available to the sentry) or the getcpu(2) system call (which
+// is relatively slow).
+func GetCPU() uint32
+
+// MaxPossibleCPU returns the highest possible CPU number, which is guaranteed
+// not to change for the lifetime of the host kernel.
+func MaxPossibleCPU() (uint32, error) {
+	const path = "/sys/devices/system/cpu/possible"
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	str := string(data)
+	// Linux: drivers/base/cpu.c:show_cpus_attr() =>
+	// include/linux/cpumask.h:cpumask_print_to_pagebuf() =>
+	// lib/bitmap.c:bitmap_print_to_pagebuf()
+	i, err := maxValueInLinuxBitmap(str)
+	if err != nil {
+		return 0, fmt.Errorf("invalid %s (%q): %v", path, str, err)
+	}
+	return uint32(i), nil
+}
+
+// maxValueInLinuxBitmap returns the maximum value specified in str, which is a
+// string emitted by Linux's lib/bitmap.c:bitmap_print_to_pagebuf(list=true).
+func maxValueInLinuxBitmap(str string) (uint64, error) {
+	str = strings.TrimSpace(str)
+	// Find the last decimal number in str.
+	idx := strings.LastIndexFunc(str, func(c rune) bool {
+		return !unicode.IsDigit(c)
+	})
+	if idx != -1 {
+		str = str[idx+1:]
+	}
+	i, err := strconv.ParseUint(str, 10, 64)
+	if err != nil {
+		return 0, err
+	}
+	return i, nil
+}