github.com/hellobchain/third_party@v0.0.0-20230331131523-deb0478a2e52/prometheus/procfs/internal/util/sysreadfile_linux.go (about)

     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  // +build !windows
    15  
    16  package util
    17  
    18  import (
    19  	"bytes"
    20  	"os"
    21  	"syscall"
    22  )
    23  
    24  // SysReadFile is a simplified ioutil.ReadFile that invokes syscall.Read directly.
    25  // https://github.com/prometheus/node_exporter/pull/728/files
    26  func SysReadFile(file string) (string, error) {
    27  	f, err := os.Open(file)
    28  	if err != nil {
    29  		return "", err
    30  	}
    31  	defer f.Close()
    32  
    33  	// On some machines, hwmon drivers are broken and return EAGAIN.  This causes
    34  	// Go's ioutil.ReadFile implementation to poll forever.
    35  	//
    36  	// Since we either want to read data or bail immediately, do the simplest
    37  	// possible read using syscall directly.
    38  	b := make([]byte, 128)
    39  	n, err := syscall.Read(int(f.Fd()), b)
    40  	if err != nil {
    41  		return "", err
    42  	}
    43  
    44  	return string(bytes.TrimSpace(b[:n])), nil
    45  }