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Source file src/github.com/prometheus/procfs/internal/util/sysreadfile.go

Documentation: github.com/prometheus/procfs/internal/util

     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  

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