3 files changed, 102 insertions, 7 deletions
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index 623d04171..f906c9f95 100644
--- a/runsc/boot/loader.go
+++ b/runsc/boot/loader.go
@@ -20,7 +20,6 @@ import (
 	"math/rand"
 	"os"
 	"os/signal"
-	"runtime"
 	"sync"
 	"sync/atomic"
 	"syscall"
@@ -201,15 +200,20 @@ func New(spec *specs.Spec, conf *Config, controllerFD, deviceFD int, ioFDs []int
 		caps,
 		auth.NewRootUserNamespace())
 
+	// Get CPU numbers from spec.
+	cpuNum, err := specutils.CalculateCPUNumber(spec)
+	if err != nil {
+		return nil, fmt.Errorf("cannot get cpus from spec: %v", err)
+	}
+
 	// Initiate the Kernel object, which is required by the Context passed
 	// to createVFS in order to mount (among other things) procfs.
 	if err = k.Init(kernel.InitKernelArgs{
-		FeatureSet:        cpuid.HostFeatureSet(),
-		Timekeeper:        tk,
-		RootUserNamespace: creds.UserNamespace,
-		NetworkStack:      networkStack,
-		// TODO: use number of logical processors from cgroups.
-		ApplicationCores:            uint(runtime.NumCPU()),
+		FeatureSet:                  cpuid.HostFeatureSet(),
+		Timekeeper:                  tk,
+		RootUserNamespace:           creds.UserNamespace,
+		NetworkStack:                networkStack,
+		ApplicationCores:            uint(cpuNum),
 		Vdso:                        vdso,
 		RootUTSNamespace:            kernel.NewUTSNamespace(spec.Hostname, "", creds.UserNamespace),
 		RootIPCNamespace:            kernel.NewIPCNamespace(creds.UserNamespace),
diff --git a/runsc/specutils/BUILD b/runsc/specutils/BUILD
index e73b2293f..f1a99ce48 100644
--- a/runsc/specutils/BUILD
+++ b/runsc/specutils/BUILD
@@ -5,6 +5,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 go_library(
     name = "specutils",
     srcs = [
+        "cpu.go",
         "namespace.go",
         "specutils.go",
     ],
diff --git a/runsc/specutils/cpu.go b/runsc/specutils/cpu.go
new file mode 100644
index 000000000..9abe26b64
--- /dev/null
+++ b/runsc/specutils/cpu.go
@@ -0,0 +1,90 @@
+// 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 specutils
+
+import (
+	"fmt"
+	"runtime"
+	"strconv"
+	"strings"
+
+	specs "github.com/opencontainers/runtime-spec/specs-go"
+)
+
+// CalculateCPUNumber calculates the number of CPUs that should be exposed
+// inside the sandbox.
+func CalculateCPUNumber(spec *specs.Spec) (int, error) {
+	// If spec does not contain CPU field, then return the number of host CPUs.
+	if spec == nil || spec.Linux == nil || spec.Linux.Resources == nil || spec.Linux.Resources.CPU == nil {
+		return runtime.NumCPU(), nil
+	}
+	cpuSpec := spec.Linux.Resources.CPU
+
+	// If cpuSpec.Cpus is specified, then parse and return that. They must be in
+	// the list format for cpusets, which is "a comma-separated list of CPU
+	// numbers and ranges of numbers, in ASCII decimal." --man 7 cpuset.
+	cpus := cpuSpec.Cpus
+	if cpus != "" {
+		cpuNum := 0
+		for _, subs := range strings.Split(cpus, ",") {
+			result, err := parseCPUNumber(subs)
+			if err != nil {
+				return 0, err
+			}
+			cpuNum += result
+		}
+		return cpuNum, nil
+	}
+
+	// If CPU.Quota and CPU.Period are specified, we can divide them to get an
+	// approximation of the number of CPUs needed.
+	if cpuSpec.Quota != nil && cpuSpec.Period != nil && *cpuSpec.Period != 0 {
+		cpuQuota := *cpuSpec.Quota
+		cpuPeriod := *cpuSpec.Period
+		return int(cpuQuota)/int(cpuPeriod) + 1, nil
+	}
+
+	// Default to number of host cpus.
+	return runtime.NumCPU(), nil
+}
+
+// parseCPUNumber converts a cpuset string into the number of cpus included in
+// the string , e.g. "3-6" -> 4.
+func parseCPUNumber(cpus string) (int, error) {
+	switch cpusSlice := strings.Split(cpus, "-"); len(cpusSlice) {
+	case 1:
+		// cpus is not a range. We must only check that it is a valid number.
+		if _, err := strconv.Atoi(cpus); err != nil {
+			return 0, fmt.Errorf("invalid individual cpu number %q", cpus)
+		}
+		return 1, nil
+	case 2:
+		// cpus is a range. We must check that start and end are valid numbers,
+		// and calculate their difference (inclusively).
+		first, err := strconv.Atoi(cpusSlice[0])
+		if err != nil || first < 0 {
+			return 0, fmt.Errorf("invalid first cpu number %q in range %q", cpusSlice[0], cpus)
+		}
+		last, err := strconv.Atoi(cpusSlice[1])
+		if err != nil || last < 0 {
+			return 0, fmt.Errorf("invalid last cpu number %q in range %q", cpusSlice[1], cpus)
+		}
+		cpuNum := last - first + 1
+		if cpuNum <= 0 {
+			return 0, fmt.Errorf("cpu range %q does not include positive number of cpus", cpus)
+		}
+	}
+	return 0, fmt.Errorf("invalid cpu string %q", cpus)
+}