/
mmap.go
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/
mmap.go
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//
// Copyright © 2017-2019 Solus Project
//
// 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.
//
package core
import (
"os"
"syscall"
)
// An MmapFile is used to easily wrap the syscall mmap() functions to be readily
// usable from golang.
// This helps heaps (pun intended) when it comes to computing the hash sum for
// very large files, such as the index and eopkg files, in a zero copy fashion.
type MmapFile struct {
f *os.File
Data []byte
len int64
m bool
}
// MapFile will attempt to mmap() the input file
func MapFile(path string) (*MmapFile, error) {
var err error
ret := &MmapFile{}
ret.f, err = os.Open(path)
if err != nil {
return nil, err
}
st, err := ret.f.Stat()
if err != nil {
ret.f.Close()
return nil, err
}
ret.len = st.Size()
ret.Data, err = syscall.Mmap(int(ret.f.Fd()), 0, int(ret.len), syscall.PROT_READ, syscall.MAP_PRIVATE)
if err != nil {
ret.f.Close()
return nil, err
}
ret.m = true
return ret, nil
}
// Close will close the previously mmapped filed
func (m *MmapFile) Close() error {
var err error
if m.f == nil {
return nil
}
if m.m {
err = syscall.Munmap(m.Data)
m.m = false
}
m.f.Close()
m.f = nil
return err
}