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