1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. 16
17. 17
18. 18
19. 19
20. 20
21. 21
22. 22
23. 23
24. 24
25. 25
26. 26
27. 27
28. 28
29. 29
30. 30
31. 31
32. 32
33. 33
34. 34
35. 35
36. 36
37. 37
38. 38
39. 39
40. 40
41. 41
42. 42
43. 43
44. 44
45. 45
46. 46
47. 47
48. 48

// 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
}