From 23ab1f8be6a1f4b5ce01e05f8ed3f6b5dae30d0b Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@lukeshu.com>
Date: Tue, 24 May 2022 21:53:28 -0600
Subject: stuff

---
 pkg/btrfs/io_device.go | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 pkg/btrfs/io_device.go

(limited to 'pkg/btrfs/io_device.go')

diff --git a/pkg/btrfs/io_device.go b/pkg/btrfs/io_device.go
new file mode 100644
index 0000000..26450b7
--- /dev/null
+++ b/pkg/btrfs/io_device.go
@@ -0,0 +1,69 @@
+package btrfs
+
+import (
+	"fmt"
+	"os"
+)
+
+type Device struct {
+	*os.File
+}
+
+func (dev Device) Size() (int64, error) {
+	fi, err := dev.Stat()
+	if err != nil {
+		return 0, err
+	}
+	return fi.Size(), nil
+}
+
+var superblockAddrs = []int64{
+	0x00_0001_0000, // 64KiB
+	0x00_0400_0000, // 64MiB
+	0x40_0000_0000, // 256GiB
+}
+
+func (dev *Device) Superblocks() ([]Ref[Superblock], error) {
+	const superblockSize = 0x1000
+
+	sz, err := dev.Size()
+	if err != nil {
+		return nil, err
+	}
+
+	var ret []Ref[Superblock]
+	for i, addr := range superblockAddrs {
+		if addr+superblockSize <= sz {
+			superblock := Ref[Superblock]{
+				dev:  dev,
+				addr: addr,
+			}
+			if err := superblock.Read(); err != nil {
+				return nil, fmt.Errorf("superblock %d: %w", i, err)
+			}
+			ret = append(ret, superblock)
+		}
+	}
+	if len(ret) == 0 {
+		return nil, fmt.Errorf("no superblocks")
+	}
+	return ret, nil
+}
+
+func (dev *Device) superblock() (ret Ref[Superblock], err error) {
+	sbs, err := dev.Superblocks()
+	if err != nil {
+		return ret, err
+	}
+	for i, sb := range sbs {
+		if err := sb.Data.ValidateChecksum(); err != nil {
+			return ret, fmt.Errorf("superblock %d: %w", i, err)
+		}
+		if i > 0 {
+			if !sb.Data.Equal(sbs[0].Data) {
+				return ret, fmt.Errorf("superblock %d and superblock %d disagree", 0, i)
+			}
+		}
+	}
+	return sbs[0], nil
+}
-- 
cgit v1.2.3-2-g168b