1 // Copyright 2018 The Prometheus Authors 2 // Licensed under the Apache License, Version 2.0 (the "License"); 3 // you may not use this file except in compliance with the License. 4 // You may obtain a copy of the License at 5 // 6 // http://www.apache.org/licenses/LICENSE-2.0 7 // 8 // Unless required by applicable law or agreed to in writing, software 9 // distributed under the License is distributed on an "AS IS" BASIS, 10 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 11 // See the License for the specific language governing permissions and 12 // limitations under the License. 13 14 //go:build (linux || darwin) && !appengine 15 // +build linux darwin 16 // +build !appengine 17 18 package util 19 20 import ( 21 "bytes" 22 "os" 23 "syscall" 24 ) 25 26 // SysReadFile is a simplified os.ReadFile that invokes syscall.Read directly. 27 // https://github.com/prometheus/node_exporter/pull/728/files 28 // 29 // Note that this function will not read files larger than 128 bytes. 30 func SysReadFile(file string) (string, error) { 31 f, err := os.Open(file) 32 if err != nil { 33 return "", err 34 } 35 defer f.Close() 36 37 // On some machines, hwmon drivers are broken and return EAGAIN. This causes 38 // Go's os.ReadFile implementation to poll forever. 39 // 40 // Since we either want to read data or bail immediately, do the simplest 41 // possible read using syscall directly. 42 const sysFileBufferSize = 128 43 b := make([]byte, sysFileBufferSize) 44 n, err := syscall.Read(int(f.Fd()), b) 45 if err != nil { 46 return "", err 47 } 48 49 return string(bytes.TrimSpace(b[:n])), nil 50 } 51