stuff

1 files changed, 123 insertions, 0 deletions

diff --git a/pkg/btrfs/io_fs.go b/pkg/btrfs/io_fs.go
new file mode 100644
index 0000000..52f742a
--- /dev/null
+++ b/pkg/btrfs/io_fs.go
@@ -0,0 +1,123 @@
+package btrfs
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+)
+
+type FS struct {
+	Devices []*Device
+
+	initErr  error
+	uuid2dev map[UUID]*Device
+	chunks   []SysChunk
+}
+
+func (fs *FS) init() error {
+	if fs.uuid2dev != nil {
+		return fs.initErr
+	}
+	fs.uuid2dev = make(map[UUID]*Device, len(fs.Devices))
+	for _, dev := range fs.Devices {
+		sbs, err := dev.Superblocks()
+		if err != nil {
+			fs.initErr = fmt.Errorf("file %q: %w", dev.Name(), err)
+			return fs.initErr
+		}
+
+		a := sbs[0].Data
+		a.Checksum = CSum{}
+		a.Self = 0
+		for i, sb := range sbs[1:] {
+			b := sb.Data
+			b.Checksum = CSum{}
+			b.Self = 0
+			if !reflect.DeepEqual(a, b) {
+				fs.initErr = fmt.Errorf("file %q: superblock %d disagrees with superblock 0",
+					dev.Name(), i+1)
+				return fs.initErr
+			}
+		}
+		sb := sbs[0]
+		if other, exists := fs.uuid2dev[sb.Data.DevItem.DevUUID]; exists {
+			fs.initErr = fmt.Errorf("file %q and file %q have the same device ID: %v",
+				other.Name(), dev.Name(), sb.Data.DevItem.DevUUID)
+			return fs.initErr
+		}
+		fs.uuid2dev[sb.Data.DevItem.DevUUID] = dev
+		syschunks, err := sb.Data.ParseSysChunkArray()
+		if err != nil {
+			fs.initErr = fmt.Errorf("file %q: %w", dev.Name(), err)
+			return fs.initErr
+		}
+		for _, chunk := range syschunks {
+			fs.chunks = append(fs.chunks, chunk)
+		}
+	}
+	return nil
+}
+
+func (fs *FS) ReadLogicalFull(laddr LogicalAddr, dat []byte) error {
+	done := LogicalAddr(0)
+	for done < LogicalAddr(len(dat)) {
+		n, err := fs.readLogicalMaybeShort(laddr+done, dat[done:])
+		if err != nil {
+			return err
+		}
+		done += LogicalAddr(n)
+	}
+	return nil
+}
+
+func (fs *FS) readLogicalMaybeShort(laddr LogicalAddr, dat []byte) (int, error) {
+	if err := fs.init(); err != nil {
+		return 0, err
+	}
+
+	type physicalAddr struct {
+		Dev  UUID
+		Addr PhysicalAddr
+	}
+
+	paddrs := make(map[physicalAddr]struct{})
+
+	for _, chunk := range fs.chunks {
+		if chunk.Offset <= uint64(laddr) && uint64(laddr) < chunk.Offset+uint64(chunk.Chunk.Size) {
+			offsetWithinChunk := uint64(laddr) - chunk.Offset
+			if offsetWithinChunk+uint64(len(dat)) > chunk.Chunk.Size {
+				dat = dat[:chunk.Chunk.Size-offsetWithinChunk]
+			}
+			for _, stripe := range chunk.Chunk.Stripes {
+				paddrs[physicalAddr{
+					Dev:  stripe.DeviceUUID,
+					Addr: PhysicalAddr(stripe.Offset + offsetWithinChunk),
+				}] = struct{}{}
+			}
+		}
+	}
+
+	if len(paddrs) == 0 {
+		return 0, fmt.Errorf("could not map logical address %v", laddr)
+	}
+
+	buf := make([]byte, len(dat))
+	first := true
+	for paddr := range paddrs {
+		dev, ok := fs.uuid2dev[paddr.Dev]
+		if !ok {
+			return 0, fmt.Errorf("device=%s does not exist", paddr.Dev)
+		}
+		if _, err := dev.ReadAt(buf, int64(paddr.Addr)); err != nil {
+			return 0, fmt.Errorf("read device=%s paddr=%v: %w", paddr.Dev, paddr.Addr, err)
+		}
+		if first {
+			copy(dat, buf)
+		} else {
+			if !bytes.Equal(dat, buf) {
+				return 0, fmt.Errorf("inconsistent stripes at laddr=%v len=%d", laddr, len(dat))
+			}
+		}
+	}
+	return len(dat), nil
+}