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- // 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
- }
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