better volume!

1 files changed, 88 insertions, 0 deletions

diff --git a/pkg/btrfs/btrfsvol/chunk.go b/pkg/btrfs/btrfsvol/chunk.go
new file mode 100644
index 0000000..112d446
--- /dev/null
+++ b/pkg/btrfs/btrfsvol/chunk.go
@@ -0,0 +1,88 @@
+package btrfsvol
+
+import (
+	"fmt"
+	"sort"
+
+	"lukeshu.com/btrfs-tools/pkg/btrfs/btrfsitem"
+	"lukeshu.com/btrfs-tools/pkg/util"
+)
+
+// logical => []physical
+type chunkMapping struct {
+	LAddr  LogicalAddr
+	PAddrs []QualifiedPhysicalAddr
+	Size   AddrDelta
+	Flags  *btrfsitem.BlockGroupFlags
+}
+
+// return -1 if 'a' is wholly to the left of 'b'
+// return 0 if there is some overlap between 'a' and 'b'
+// return 1 if 'a is wholly to the right of 'b'
+func (a chunkMapping) cmpRange(b chunkMapping) int {
+	switch {
+	case a.LAddr.Add(a.Size) <= b.LAddr:
+		// 'a' is wholly to the left of 'b'.
+		return -1
+	case b.LAddr.Add(b.Size) <= a.LAddr:
+		// 'a' is wholly to the right of 'b'.
+		return 1
+	default:
+		// There is some overlap.
+		return 0
+	}
+}
+
+func (a chunkMapping) union(rest ...chunkMapping) (chunkMapping, error) {
+	// sanity check
+	for _, chunk := range rest {
+		if a.cmpRange(chunk) != 0 {
+			return chunkMapping{}, fmt.Errorf("chunks don't overlap")
+		}
+	}
+	chunks := append([]chunkMapping{a}, rest...)
+	// figure out the logical range (.LAddr and .Size)
+	beg := chunks[0].LAddr
+	end := chunks[0].LAddr.Add(chunks[0].Size)
+	for _, chunk := range chunks {
+		beg = util.Min(beg, chunk.LAddr)
+		end = util.Max(end, chunk.LAddr.Add(chunk.Size))
+	}
+	ret := chunkMapping{
+		LAddr: beg,
+		Size:  end.Sub(beg),
+	}
+	// figure out the physical stripes (.PAddrs)
+	paddrs := make(map[QualifiedPhysicalAddr]struct{})
+	for _, chunk := range chunks {
+		offsetWithinRet := chunk.LAddr.Sub(ret.LAddr)
+		for _, stripe := range chunk.PAddrs {
+			paddrs[QualifiedPhysicalAddr{
+				Dev:  stripe.Dev,
+				Addr: stripe.Addr.Add(-offsetWithinRet),
+			}] = struct{}{}
+		}
+	}
+	ret.PAddrs = make([]QualifiedPhysicalAddr, 0, len(paddrs))
+	for paddr := range paddrs {
+		ret.PAddrs = append(ret.PAddrs, paddr)
+	}
+	sort.Slice(ret.PAddrs, func(i, j int) bool {
+		return ret.PAddrs[i].Cmp(ret.PAddrs[j]) < 0
+	})
+	// figure out the flags (.Flags)
+	for _, chunk := range chunks {
+		if chunk.Flags == nil {
+			continue
+		}
+		if ret.Flags == nil {
+			val := *chunk.Flags
+			ret.Flags = &val
+		}
+		if *ret.Flags != *chunk.Flags {
+			return ret, fmt.Errorf("mismatch flags: %v != %v", *ret.Flags, *chunk.Flags)
+		}
+	}
+	// done
+	return ret, nil
+}