Function WriteFile

msgp/file.go:69–90

WriteFile writes a file from 'src' using memory mapping. It overwrites the entire contents of the previous file. The mapping size is calculated using the `Msgsize()` method of 'src', so it must produce a result equal to or greater than the actual encoded size of the object. Otherwise, a fault (SIGBU

(src MarshalSizer, file *os.File)

// (Linux users should run a kernel and filesystem
// that support fallocate(2) for the best results.)
func WriteFile(src MarshalSizer, file *os.File) error {
	sz := src.Msgsize()
	err := fallocate(file, int64(sz))
	if err != nil {
		return err
	}
	data, err := syscall.Mmap(int(file.Fd()), 0, sz, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
	if err != nil {
		return err
	}
	adviseWrite(data)
	chunk := data[:0]
	chunk, err = src.MarshalMsg(chunk)
	if err != nil {
		return err
	}
	uerr := syscall.Munmap(data)
	if uerr != nil {
		return uerr
	}
	return file.Truncate(int64(len(chunk)))
}