Add docker command line args support for --cpuset-cpus and --cpus

`docker run --cpuset-cpus=/--cpus=` will generate cpu resource info in config.json
(runtime spec file). When nginx worker_connections is configured as auto, the worker is
generated according to the number of CPUs. If the cgroup is already set on the host, but
it is not displayed correctly in the sandbox, performance may be degraded.

This patch can get cpus info from spec file and apply to sentry on bootup, so the
/proc/cpuinfo can show the correct cpu numbers. `lscpu` and other commands rely on
`/sys/devices/system/cpu/online` are also affected by this patch.

e.g.

--cpuset-cpus=2,3   ->  cpu number:2
--cpuset-cpus=4-7   ->  cpu number:4
--cpus=2.8          ->  cpu number:3
--cpus=0.5          ->  cpu number:1
Change-Id: Ideb22e125758d4322a12be7c51795f8018e3d316
PiperOrigin-RevId: 213685199

2 files changed, 91 insertions, 0 deletions

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)
+}