1 files changed, 89 insertions, 0 deletions
diff --git a/lib/btrfs/btrfsvol/devext.go b/lib/btrfs/btrfsvol/devext.go
new file mode 100644
index 0000000..43c6255
--- /dev/null
+++ b/lib/btrfs/btrfsvol/devext.go
@@ -0,0 +1,89 @@
+package btrfsvol
+
+import (
+	"fmt"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/util"
+)
+
+// physical => logical
+type devextMapping struct {
+	PAddr      PhysicalAddr
+	LAddr      LogicalAddr
+	Size       AddrDelta
+	SizeLocked bool
+	Flags      *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 devextMapping) cmpRange(b devextMapping) int {
+	switch {
+	case a.PAddr.Add(a.Size) <= b.PAddr:
+		// 'a' is wholly to the left of 'b'.
+		return -1
+	case b.PAddr.Add(b.Size) <= a.PAddr:
+		// 'a' is wholly to the right of 'b'.
+		return 1
+	default:
+		// There is some overlap.
+		return 0
+	}
+}
+
+func (a devextMapping) union(rest ...devextMapping) (devextMapping, error) {
+	// sanity check
+	for _, ext := range rest {
+		if a.cmpRange(ext) != 0 {
+			return devextMapping{}, fmt.Errorf("devexts don't overlap")
+		}
+	}
+	exts := append([]devextMapping{a}, rest...)
+	// figure out the physical range (.PAddr and .Size)
+	beg := exts[0].PAddr
+	end := beg.Add(exts[0].Size)
+	for _, ext := range exts {
+		beg = util.Min(beg, ext.PAddr)
+		end = util.Max(end, ext.PAddr.Add(ext.Size))
+	}
+	ret := devextMapping{
+		PAddr: beg,
+		Size:  end.Sub(beg),
+	}
+	for _, ext := range exts {
+		if ext.SizeLocked {
+			ret.SizeLocked = true
+			if ret.Size != ext.Size {
+				return devextMapping{}, fmt.Errorf("member devext has locked size=%v, but union would have size=%v",
+					ext.Size, ret.Size)
+			}
+		}
+	}
+	// figure out the logical range (.LAddr)
+	first := true
+	for _, ext := range exts {
+		offsetWithinRet := ext.PAddr.Sub(ret.PAddr)
+		laddr := ext.LAddr.Add(-offsetWithinRet)
+		if first {
+			ret.LAddr = laddr
+		} else if laddr != ret.LAddr {
+			return ret, fmt.Errorf("devexts don't agree on laddr: %v != %v", ret.LAddr, laddr)
+		}
+	}
+	// figure out the flags (.Flags)
+	for _, ext := range exts {
+		if ext.Flags == nil {
+			continue
+		}
+		if ret.Flags == nil {
+			val := *ext.Flags
+			ret.Flags = &val
+		}
+		if *ret.Flags != *ext.Flags {
+			return ret, fmt.Errorf("mismatch flags: %v != %v", *ret.Flags, *ext.Flags)
+		}
+	}
+	// done
+	return ret, nil
+}