cubefs

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// Copyright 2018 The Prometheus Authors
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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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//go:build (linux || darwin) && !appengine
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// +build linux darwin
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// +build !appengine
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package util
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import (
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	"bytes"
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	"os"
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	"syscall"
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)
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// SysReadFile is a simplified os.ReadFile that invokes syscall.Read directly.
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// https://github.com/prometheus/node_exporter/pull/728/files
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//
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// Note that this function will not read files larger than 128 bytes.
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func SysReadFile(file string) (string, error) {
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	f, err := os.Open(file)
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	if err != nil {
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		return "", err
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	}
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	defer f.Close()
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	// On some machines, hwmon drivers are broken and return EAGAIN.  This causes
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	// Go's os.ReadFile implementation to poll forever.
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	//
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	// Since we either want to read data or bail immediately, do the simplest
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	// possible read using syscall directly.
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	const sysFileBufferSize = 128
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	b := make([]byte, sysFileBufferSize)
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	n, err := syscall.Read(int(f.Fd()), b)
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	if err != nil {
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		return "", err
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	}
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	return string(bytes.TrimSpace(b[:n])), nil
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}
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