1 files changed, 96 insertions, 0 deletions
diff --git a/pkg/btrfs/io1_pv.go b/pkg/btrfs/io1_pv.go
new file mode 100644
index 0000000..b9f7ea4
--- /dev/null
+++ b/pkg/btrfs/io1_pv.go
@@ -0,0 +1,96 @@
+package btrfs
+
+import (
+	"fmt"
+	"os"
+
+	"lukeshu.com/btrfs-tools/pkg/binstruct"
+	"lukeshu.com/btrfs-tools/pkg/btrfs/btrfsvol"
+	"lukeshu.com/btrfs-tools/pkg/util"
+)
+
+type Device struct {
+	*os.File
+
+	cacheSuperblocks []*util.Ref[btrfsvol.PhysicalAddr, Superblock]
+	cacheSuperblock  *util.Ref[btrfsvol.PhysicalAddr, Superblock]
+}
+
+var _ util.File[btrfsvol.PhysicalAddr] = (*Device)(nil)
+
+func (dev Device) Size() (btrfsvol.PhysicalAddr, error) {
+	fi, err := dev.Stat()
+	if err != nil {
+		return 0, err
+	}
+	return btrfsvol.PhysicalAddr(fi.Size()), nil
+}
+
+func (dev *Device) ReadAt(dat []byte, paddr btrfsvol.PhysicalAddr) (int, error) {
+	return dev.File.ReadAt(dat, int64(paddr))
+}
+
+func (dev *Device) WriteAt(dat []byte, paddr btrfsvol.PhysicalAddr) (int, error) {
+	return dev.File.WriteAt(dat, int64(paddr))
+}
+
+var SuperblockAddrs = []btrfsvol.PhysicalAddr{
+	0x00_0001_0000, // 64KiB
+	0x00_0400_0000, // 64MiB
+	0x40_0000_0000, // 256GiB
+}
+
+func (dev *Device) Superblocks() ([]*util.Ref[btrfsvol.PhysicalAddr, Superblock], error) {
+	if dev.cacheSuperblocks != nil {
+		return dev.cacheSuperblocks, nil
+	}
+	superblockSize := btrfsvol.PhysicalAddr(binstruct.StaticSize(Superblock{}))
+
+	sz, err := dev.Size()
+	if err != nil {
+		return nil, err
+	}
+
+	var ret []*util.Ref[btrfsvol.PhysicalAddr, Superblock]
+	for i, addr := range SuperblockAddrs {
+		if addr+superblockSize <= sz {
+			superblock := &util.Ref[btrfsvol.PhysicalAddr, Superblock]{
+				File: dev,
+				Addr: addr,
+			}
+			if err := superblock.Read(); err != nil {
+				return nil, fmt.Errorf("superblock %v: %w", i, err)
+			}
+			ret = append(ret, superblock)
+		}
+	}
+	if len(ret) == 0 {
+		return nil, fmt.Errorf("no superblocks")
+	}
+	dev.cacheSuperblocks = ret
+	return ret, nil
+}
+
+func (dev *Device) Superblock() (*util.Ref[btrfsvol.PhysicalAddr, Superblock], error) {
+	if dev.cacheSuperblock != nil {
+		return dev.cacheSuperblock, nil
+	}
+	sbs, err := dev.Superblocks()
+	if err != nil {
+		return nil, err
+	}
+
+	for i, sb := range sbs {
+		if err := sb.Data.ValidateChecksum(); err != nil {
+			return nil, fmt.Errorf("superblock %v: %w", i, err)
+		}
+		if i > 0 {
+			if !sb.Data.Equal(sbs[0].Data) {
+				return nil, fmt.Errorf("superblock %v and superblock %v disagree", 0, i)
+			}
+		}
+	}
+
+	dev.cacheSuperblock = sbs[0]
+	return sbs[0], nil
+}