db migration: if stage_snapshots > 0, then create prohibit_new_downloads.lock file (#9036)

it will protect existing nodes from downloading `v2` files - even if
they do upgrade

erigon-lib/downloader/downloader.go

@@ -140,13 +140,13 @@ func New(ctx context.Context, cfg *downloadercfg.Cfg, dirs datadir.Dirs, logger
 	return d, nil
 }
 
-const prohibitNewDownloadsFileName = "prohibit_new_downloads.lock"
+const ProhibitNewDownloadsFileName = "prohibit_new_downloads.lock"
 
 // Erigon "download once" - means restart/upgrade/downgrade will not download files (and will be fast)
 // After "download once" - Erigon will produce and seed new files
 // Downloader will able: seed new files (already existing on FS), download uncomplete parts of existing files (if Verify found some bad parts)
 func (d *Downloader) prohibitNewDownloads() error {
-	fPath := filepath.Join(d.SnapDir(), prohibitNewDownloadsFileName)
+	fPath := filepath.Join(d.SnapDir(), ProhibitNewDownloadsFileName)
 	f, err := os.Create(fPath)
 	if err != nil {
 		return err
@@ -158,7 +158,7 @@ func (d *Downloader) prohibitNewDownloads() error {
 	return nil
 }
 func (d *Downloader) newDownloadsAreProhibited() bool {
-	return dir.FileExist(filepath.Join(d.SnapDir(), prohibitNewDownloadsFileName))
+	return dir.FileExist(filepath.Join(d.SnapDir(), ProhibitNewDownloadsFileName))
 }
 
 func (d *Downloader) MainLoopInBackground(silent bool) {

migrations/migrations.go

@@ -4,9 +4,10 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"github.com/ledgerwatch/erigon-lib/common"
 	"path/filepath"
 
+	"github.com/ledgerwatch/erigon-lib/common"
+
 	"github.com/ledgerwatch/erigon-lib/common/datadir"
 	"github.com/ledgerwatch/erigon-lib/kv"
 	"github.com/ledgerwatch/erigon/core/rawdb"
@@ -35,6 +36,7 @@ var migrations = map[kv.Label][]Migration{
 		dbSchemaVersion5,
 		TxsBeginEnd,
 		TxsV3,
+		ProhibitNewDownloadsLock,
 	},
 	kv.TxPoolDB: {},
 	kv.SentryDB: {},

migrations/prohibit_new_downloads_lock.go

@@ -0,0 +1,49 @@
+package migrations
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+
+	"github.com/ledgerwatch/erigon-lib/common/datadir"
+	"github.com/ledgerwatch/erigon-lib/common/dir"
+	"github.com/ledgerwatch/erigon-lib/downloader"
+	"github.com/ledgerwatch/erigon-lib/kv"
+	"github.com/ledgerwatch/erigon/eth/stagedsync/stages"
+	"github.com/ledgerwatch/log/v3"
+)
+
+var ProhibitNewDownloadsLock = Migration{
+	Name: "prohibit_new_downloads_lock",
+	Up: func(db kv.RwDB, dirs datadir.Dirs, progress []byte, BeforeCommit Callback, logger log.Logger) (err error) {
+		tx, err := db.BeginRw(context.Background())
+		if err != nil {
+			return err
+		}
+		defer tx.Rollback()
+
+		snapshotsStageProgress, err := stages.GetStageProgress(tx, stages.Snapshots)
+		if err != nil {
+			return err
+		}
+		if snapshotsStageProgress > 0 {
+			fPath := filepath.Join(dirs.Snap, downloader.ProhibitNewDownloadsFileName)
+			if !dir.FileExist(fPath) {
+				f, err := os.Create(fPath)
+				if err != nil {
+					return err
+				}
+				defer f.Close()
+				if err := f.Sync(); err != nil {
+					return err
+				}
+			}
+		}
+
+		// This migration is no-op, but it forces the migration mechanism to apply it and thus write the DB schema version info
+		if err := BeforeCommit(tx, nil, true); err != nil {
+			return err
+		}
+		return tx.Commit()
+	},
+}