From 2e1946a200bf2d6374ecc097916d664f49fd8417 Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@lukeshu.com>
Date: Sun, 5 Mar 2023 21:54:14 -0700
Subject: Factor out the device-scan loop from rebuildmappings in to btrfsutil

---
 lib/btrfsutil/scan.go | 148 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100644 lib/btrfsutil/scan.go

(limited to 'lib/btrfsutil/scan.go')

diff --git a/lib/btrfsutil/scan.go b/lib/btrfsutil/scan.go
new file mode 100644
index 0000000..97220aa
--- /dev/null
+++ b/lib/btrfsutil/scan.go
@@ -0,0 +1,148 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package btrfsutil
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/datawire/dlib/dgroup"
+	"github.com/datawire/dlib/dlog"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/binstruct"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfssum"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfstree"
+	"git.lukeshu.com/btrfs-progs-ng/lib/btrfs/btrfsvol"
+	"git.lukeshu.com/btrfs-progs-ng/lib/diskio"
+	"git.lukeshu.com/btrfs-progs-ng/lib/textui"
+)
+
+var sbSize = btrfsvol.PhysicalAddr(binstruct.StaticSize(btrfstree.Superblock{}))
+
+type DeviceScannerFactory[Stats comparable, Result any] func(ctx context.Context, sb btrfstree.Superblock, numBytes btrfsvol.PhysicalAddr, numSectors int) DeviceScanner[Stats, Result]
+
+type DeviceScanner[Stats comparable, Result any] interface {
+	ScanStats() Stats
+	ScanSector(ctx context.Context, dev *btrfs.Device, paddr btrfsvol.PhysicalAddr) error
+	ScanNode(ctx context.Context, nodeRef *diskio.Ref[btrfsvol.PhysicalAddr, btrfstree.Node]) error
+	ScanDone(ctx context.Context) (Result, error)
+}
+
+type scanStats[T comparable] struct {
+	portion textui.Portion[btrfsvol.PhysicalAddr]
+	stats   T
+}
+
+func (s scanStats[T]) String() string {
+	return textui.Sprintf("scanned %v (%v)",
+		s.portion, s.stats)
+}
+
+func ScanDevices[Stats comparable, Result any](ctx context.Context, fs *btrfs.FS, newScanner DeviceScannerFactory[Stats, Result]) (map[btrfsvol.DeviceID]Result, error) {
+	grp := dgroup.NewGroup(ctx, dgroup.GroupConfig{})
+	var mu sync.Mutex
+	result := make(map[btrfsvol.DeviceID]Result)
+	for id, dev := range fs.LV.PhysicalVolumes() {
+		id := id
+		dev := dev
+		grp.Go(fmt.Sprintf("dev-%d", id), func(ctx context.Context) error {
+			devResult, err := ScanOneDevice[Stats, Result](ctx, dev, newScanner)
+			if err != nil {
+				return err
+			}
+			mu.Lock()
+			result[id] = devResult
+			mu.Unlock()
+			return nil
+		})
+	}
+	if err := grp.Wait(); err != nil {
+		return nil, err
+	}
+	return result, nil
+}
+
+func ScanOneDevice[Stats comparable, Result any](ctx context.Context, dev *btrfs.Device, newScanner DeviceScannerFactory[Stats, Result]) (Result, error) {
+	ctx = dlog.WithField(ctx, "scandevices.dev", dev.Name())
+
+	sb, err := dev.Superblock()
+	if err != nil {
+		var zero Result
+		return zero, err
+	}
+	numBytes := dev.Size()
+	if sb.NodeSize < sb.SectorSize {
+		var zero Result
+		return zero, fmt.Errorf("node_size(%v) < sector_size(%v)",
+			sb.NodeSize, sb.SectorSize)
+	}
+	if sb.SectorSize != btrfssum.BlockSize {
+		// TODO: probably handle this?
+		var zero Result
+		return zero, fmt.Errorf("sector_size(%v) != btrfssum.BlockSize",
+			sb.SectorSize)
+	}
+	numSectors := int(numBytes / btrfssum.BlockSize)
+
+	scanner := newScanner(ctx, *sb, numBytes, numSectors)
+
+	progressWriter := textui.NewProgress[scanStats[Stats]](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second))
+	var stats scanStats[Stats]
+	stats.portion.D = numBytes
+
+	var minNextNode btrfsvol.PhysicalAddr
+	for i := 0; i < numSectors; i++ {
+		if ctx.Err() != nil {
+			var zero Result
+			return zero, ctx.Err()
+		}
+		pos := btrfsvol.PhysicalAddr(i * btrfssum.BlockSize)
+		stats.portion.N = pos
+		stats.stats = scanner.ScanStats()
+		progressWriter.Set(stats)
+
+		if err := scanner.ScanSector(ctx, dev, pos); err != nil {
+			var zero Result
+			return zero, err
+		}
+
+		checkForNode := pos >= minNextNode && pos+btrfsvol.PhysicalAddr(sb.NodeSize) <= numBytes
+		if checkForNode {
+			for _, sbAddr := range btrfs.SuperblockAddrs {
+				if sbAddr <= pos && pos < sbAddr+sbSize {
+					checkForNode = false
+					break
+				}
+			}
+		}
+
+		if checkForNode {
+			nodeRef, err := btrfstree.ReadNode[btrfsvol.PhysicalAddr](dev, *sb, pos, btrfstree.NodeExpectations{})
+			if err != nil {
+				if !errors.Is(err, btrfstree.ErrNotANode) {
+					dlog.Errorf(ctx, "error: %v", err)
+				}
+			} else {
+				if err := scanner.ScanNode(ctx, nodeRef); err != nil {
+					var zero Result
+					return zero, err
+				}
+				minNextNode = pos + btrfsvol.PhysicalAddr(sb.NodeSize)
+			}
+			btrfstree.FreeNodeRef(nodeRef)
+		}
+	}
+
+	stats.portion.N = numBytes
+	stats.stats = scanner.ScanStats()
+	progressWriter.Set(stats)
+	progressWriter.Done()
+
+	return scanner.ScanDone(ctx)
+}
-- 
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