// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later

package btrfsitem

import (
	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsprim"
	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
)

// A DevExtent tracks allocation of the physical address space.
//
// Compare with:
//   - BlockGroups, which track allocation of the logical address space.
//   - Chunks, which map logical addresses to physical addresses.
//
// The relationship between the three is
//
//	DevExtent---[many:one]---Chunk---[one:one]---BlockGroup
//
// The device ID identifies which Dev item describes the physical
// volume that the DevExtent is on.
//
// Key:
//
//	key.objectid = device_id
//	key.offset   = physical_addr
type DevExtent struct { // trivial DEV_EXTENT=204
	ChunkTree     btrfsprim.ObjID      `bin:"off=0, siz=8"`  // always CHUNK_TREE_OBJECTID
	ChunkObjectID btrfsprim.ObjID      `bin:"off=8, siz=8"`  // which chunk within .ChunkTree owns this extent, always FIRST_CHUNK_TREE_OBJECTID
	ChunkOffset   btrfsvol.LogicalAddr `bin:"off=16, siz=8"` // offset of the CHUNK_ITEM that owns this extent, within the .ChunkObjectID
	Length        btrfsvol.AddrDelta   `bin:"off=24, siz=8"`
	ChunkTreeUUID btrfsprim.UUID       `bin:"off=32, siz=16"`
	binstruct.End `bin:"off=48"`
}

func (devext DevExtent) Mapping(key btrfsprim.Key) btrfsvol.Mapping {
	return btrfsvol.Mapping{
		LAddr: devext.ChunkOffset,
		PAddr: btrfsvol.QualifiedPhysicalAddr{
			Dev:  btrfsvol.DeviceID(key.ObjectID),
			Addr: btrfsvol.PhysicalAddr(key.Offset),
		},
		Size:       devext.Length,
		SizeLocked: true,
	}
}