68 lines
2.1 KiB
Go
68 lines
2.1 KiB
Go
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// Copyright 2018 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package hostcpu provides utilities for working with CPU information provided
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// by a host Linux kernel.
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package hostcpu
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import (
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"fmt"
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"io/ioutil"
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"strconv"
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"strings"
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"unicode"
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)
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// GetCPU returns the caller's current CPU number, without using the Linux VDSO
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// (which is not available to the sentry) or the getcpu(2) system call (which
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// is relatively slow).
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func GetCPU() uint32
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// MaxPossibleCPU returns the highest possible CPU number, which is guaranteed
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// not to change for the lifetime of the host kernel.
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func MaxPossibleCPU() (uint32, error) {
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const path = "/sys/devices/system/cpu/possible"
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data, err := ioutil.ReadFile(path)
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if err != nil {
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return 0, err
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}
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str := string(data)
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// Linux: drivers/base/cpu.c:show_cpus_attr() =>
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// include/linux/cpumask.h:cpumask_print_to_pagebuf() =>
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// lib/bitmap.c:bitmap_print_to_pagebuf()
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i, err := maxValueInLinuxBitmap(str)
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if err != nil {
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return 0, fmt.Errorf("invalid %s (%q): %v", path, str, err)
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}
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return uint32(i), nil
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}
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// maxValueInLinuxBitmap returns the maximum value specified in str, which is a
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// string emitted by Linux's lib/bitmap.c:bitmap_print_to_pagebuf(list=true).
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func maxValueInLinuxBitmap(str string) (uint64, error) {
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str = strings.TrimSpace(str)
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// Find the last decimal number in str.
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idx := strings.LastIndexFunc(str, func(c rune) bool {
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return !unicode.IsDigit(c)
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})
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if idx != -1 {
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str = str[idx+1:]
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}
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i, err := strconv.ParseUint(str, 10, 64)
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if err != nil {
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return 0, err
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}
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return i, nil
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}
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