device.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"os"

	"github.com/ncw/directio"
)

type Device struct {
	*os.File
	Size       int64
	alignedBuf []byte
}

func Open(name string) (Device, error) {
	f, err := directio.OpenFile(name, os.O_RDWR, 0)
	if err != nil {
		return Device{}, err
	}
	fi, err := f.Stat()
	if err != nil {
		return Device{}, err
	}
	fm := fi.Mode()
	if fm&os.ModeDevice == 0 {
		return Device{}, fmt.Errorf("%s is not a block device", name)
	}

	sz, err := f.Seek(0, io.SeekEnd)
	if err != nil {
		return Device{}, fmt.Errorf("failed to get size of device: %w", err)
	}
	_, err = f.Seek(0, io.SeekStart)
	if err != nil {
		return Device{}, fmt.Errorf("failed to seek to start of device: %w", err)
	}
	if sz <= 0 {
		return Device{}, fmt.Errorf("device size is zero or negative")
	}

	return Device{File: f, Size: sz}, nil
}

func (d Device) Write(b []byte) error {
	if len(b)%directio.BlockSize != 0 {
		return fmt.Errorf("write size %d is not a multiple of %d", len(b), directio.BlockSize)
	}
	if len(d.alignedBuf) < len(b) {
		d.alignedBuf = directio.AlignedBlock(len(b))
	}
	copy(d.alignedBuf, b)
	_, err := d.File.Write(d.alignedBuf[:len(b)])
	return err
}

func (d Device) Verify(b []byte) error {
	if len(b)%directio.BlockSize != 0 {
		return fmt.Errorf("verify size %d is not a multiple of %d", len(b), directio.BlockSize)
	}
	if len(d.alignedBuf) < len(b) {
		d.alignedBuf = directio.AlignedBlock(len(b))
	}
	readBuf := d.alignedBuf[:len(b)]
	_, err := io.ReadFull(d.File, readBuf)
	if err != nil {
		return fmt.Errorf("read error: %w", err)
	}
	if !bytes.Equal(b, readBuf) {
		return fmt.Errorf("data mismatch")
	}
	return nil
}