core/rawdb, cmd, ethdb, eth: implement freezer tail deletion (#23954)

* core/rawdb, cmd, ethdb, eth: implement freezer tail deletion

* core/rawdb: address comments from martin and sina

* core/rawdb: fixes cornercase in tail deletion

* core/rawdb: separate metadata into a standalone file

* core/rawdb: remove unused code

* core/rawdb: add random test

* core/rawdb: polish code

* core/rawdb: fsync meta file before manipulating the index

* core/rawdb: fix typo

* core/rawdb: address comments

core/rawdb/freezer_utils.go

@@ -0,0 +1,120 @@
+// Copyright 2022 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package rawdb
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// copyFrom copies data from 'srcPath' at offset 'offset' into 'destPath'.
+// The 'destPath' is created if it doesn't exist, otherwise it is overwritten.
+// Before the copy is executed, there is a callback can be registered to
+// manipulate the dest file.
+// It is perfectly valid to have destPath == srcPath.
+func copyFrom(srcPath, destPath string, offset uint64, before func(f *os.File) error) error {
+	// Create a temp file in the same dir where we want it to wind up
+	f, err := ioutil.TempFile(filepath.Dir(destPath), "*")
+	if err != nil {
+		return err
+	}
+	fname := f.Name()
+
+	// Clean up the leftover file
+	defer func() {
+		if f != nil {
+			f.Close()
+		}
+		os.Remove(fname)
+	}()
+	// Apply the given function if it's not nil before we copy
+	// the content from the src.
+	if before != nil {
+		if err := before(f); err != nil {
+			return err
+		}
+	}
+	// Open the source file
+	src, err := os.Open(srcPath)
+	if err != nil {
+		return err
+	}
+	if _, err = src.Seek(int64(offset), 0); err != nil {
+		src.Close()
+		return err
+	}
+	// io.Copy uses 32K buffer internally.
+	_, err = io.Copy(f, src)
+	if err != nil {
+		src.Close()
+		return err
+	}
+	// Rename the temporary file to the specified dest name.
+	// src may be same as dest, so needs to be closed before
+	// we do the final move.
+	src.Close()
+
+	if err := f.Close(); err != nil {
+		return err
+	}
+	f = nil
+
+	if err := os.Rename(fname, destPath); err != nil {
+		return err
+	}
+	return nil
+}
+
+// openFreezerFileForAppend opens a freezer table file and seeks to the end
+func openFreezerFileForAppend(filename string) (*os.File, error) {
+	// Open the file without the O_APPEND flag
+	// because it has differing behaviour during Truncate operations
+	// on different OS's
+	file, err := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, 0644)
+	if err != nil {
+		return nil, err
+	}
+	// Seek to end for append
+	if _, err = file.Seek(0, io.SeekEnd); err != nil {
+		return nil, err
+	}
+	return file, nil
+}
+
+// openFreezerFileForReadOnly opens a freezer table file for read only access
+func openFreezerFileForReadOnly(filename string) (*os.File, error) {
+	return os.OpenFile(filename, os.O_RDONLY, 0644)
+}
+
+// openFreezerFileTruncated opens a freezer table making sure it is truncated
+func openFreezerFileTruncated(filename string) (*os.File, error) {
+	return os.OpenFile(filename, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
+}
+
+// truncateFreezerFile resizes a freezer table file and seeks to the end
+func truncateFreezerFile(file *os.File, size int64) error {
+	if err := file.Truncate(size); err != nil {
+		return err
+	}
+	// Seek to end for append
+	if _, err := file.Seek(0, io.SeekEnd); err != nil {
+		return err
+	}
+	return nil
+}