您最多选择25个主题
主题必须以字母或数字开头，可以包含连字符 (-)，并且长度不得超过35个字符
274 行
8.7 KiB
274 行
8.7 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style license that can be
|
|
// found in the LICENSE file. See the AUTHORS file for names of contributors.
|
|
|
|
#include "db/log_reader.h"
|
|
|
|
#include <cstdio>
|
|
|
|
#include "leveldb/env.h"
|
|
#include "util/coding.h"
|
|
#include "util/crc32c.h"
|
|
|
|
namespace leveldb {
|
|
namespace log {
|
|
|
|
Reader::Reporter::~Reporter() = default;
|
|
|
|
Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
|
|
uint64_t initial_offset)
|
|
: file_(file),
|
|
reporter_(reporter),
|
|
checksum_(checksum),
|
|
backing_store_(new char[kBlockSize]),
|
|
buffer_(),
|
|
eof_(false),
|
|
last_record_offset_(0),
|
|
end_of_buffer_offset_(0),
|
|
initial_offset_(initial_offset),
|
|
resyncing_(initial_offset > 0) {}
|
|
|
|
Reader::~Reader() { delete[] backing_store_; }
|
|
|
|
bool Reader::SkipToInitialBlock() {
|
|
const size_t offset_in_block = initial_offset_ % kBlockSize;
|
|
uint64_t block_start_location = initial_offset_ - offset_in_block;
|
|
|
|
// Don't search a block if we'd be in the trailer
|
|
if (offset_in_block > kBlockSize - 6) {
|
|
block_start_location += kBlockSize;
|
|
}
|
|
|
|
end_of_buffer_offset_ = block_start_location;
|
|
|
|
// Skip to start of first block that can contain the initial record
|
|
if (block_start_location > 0) {
|
|
Status skip_status = file_->Skip(block_start_location);
|
|
if (!skip_status.ok()) {
|
|
ReportDrop(block_start_location, skip_status);
|
|
return false;
|
|
}
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
bool Reader::ReadRecord(Slice* record, std::string* scratch) {
|
|
if (last_record_offset_ < initial_offset_) {
|
|
if (!SkipToInitialBlock()) {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
scratch->clear();
|
|
record->clear();
|
|
bool in_fragmented_record = false;
|
|
// Record offset of the logical record that we're reading
|
|
// 0 is a dummy value to make compilers happy
|
|
uint64_t prospective_record_offset = 0;
|
|
|
|
Slice fragment;
|
|
while (true) {
|
|
const unsigned int record_type = ReadPhysicalRecord(&fragment);
|
|
|
|
// ReadPhysicalRecord may have only had an empty trailer remaining in its
|
|
// internal buffer. Calculate the offset of the next physical record now
|
|
// that it has returned, properly accounting for its header size.
|
|
uint64_t physical_record_offset =
|
|
end_of_buffer_offset_ - buffer_.size() - kHeaderSize - fragment.size();
|
|
|
|
if (resyncing_) {
|
|
if (record_type == kMiddleType) {
|
|
continue;
|
|
} else if (record_type == kLastType) {
|
|
resyncing_ = false;
|
|
continue;
|
|
} else {
|
|
resyncing_ = false;
|
|
}
|
|
}
|
|
|
|
switch (record_type) {
|
|
case kFullType:
|
|
if (in_fragmented_record) {
|
|
// Handle bug in earlier versions of log::Writer where
|
|
// it could emit an empty kFirstType record at the tail end
|
|
// of a block followed by a kFullType or kFirstType record
|
|
// at the beginning of the next block.
|
|
if (!scratch->empty()) {
|
|
ReportCorruption(scratch->size(), "partial record without end(1)");
|
|
}
|
|
}
|
|
prospective_record_offset = physical_record_offset;
|
|
scratch->clear();
|
|
*record = fragment;
|
|
last_record_offset_ = prospective_record_offset;
|
|
return true;
|
|
|
|
case kFirstType:
|
|
if (in_fragmented_record) {
|
|
// Handle bug in earlier versions of log::Writer where
|
|
// it could emit an empty kFirstType record at the tail end
|
|
// of a block followed by a kFullType or kFirstType record
|
|
// at the beginning of the next block.
|
|
if (!scratch->empty()) {
|
|
ReportCorruption(scratch->size(), "partial record without end(2)");
|
|
}
|
|
}
|
|
prospective_record_offset = physical_record_offset;
|
|
scratch->assign(fragment.data(), fragment.size());
|
|
in_fragmented_record = true;
|
|
break;
|
|
|
|
case kMiddleType:
|
|
if (!in_fragmented_record) {
|
|
ReportCorruption(fragment.size(),
|
|
"missing start of fragmented record(1)");
|
|
} else {
|
|
scratch->append(fragment.data(), fragment.size());
|
|
}
|
|
break;
|
|
|
|
case kLastType:
|
|
if (!in_fragmented_record) {
|
|
ReportCorruption(fragment.size(),
|
|
"missing start of fragmented record(2)");
|
|
} else {
|
|
scratch->append(fragment.data(), fragment.size());
|
|
*record = Slice(*scratch);
|
|
last_record_offset_ = prospective_record_offset;
|
|
return true;
|
|
}
|
|
break;
|
|
|
|
case kEof:
|
|
if (in_fragmented_record) {
|
|
// This can be caused by the writer dying immediately after
|
|
// writing a physical record but before completing the next; don't
|
|
// treat it as a corruption, just ignore the entire logical record.
|
|
scratch->clear();
|
|
}
|
|
return false;
|
|
|
|
case kBadRecord:
|
|
if (in_fragmented_record) {
|
|
ReportCorruption(scratch->size(), "error in middle of record");
|
|
in_fragmented_record = false;
|
|
scratch->clear();
|
|
}
|
|
break;
|
|
|
|
default: {
|
|
char buf[40];
|
|
std::snprintf(buf, sizeof(buf), "unknown record type %u", record_type);
|
|
ReportCorruption(
|
|
(fragment.size() + (in_fragmented_record ? scratch->size() : 0)),
|
|
buf);
|
|
in_fragmented_record = false;
|
|
scratch->clear();
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
uint64_t Reader::LastRecordOffset() { return last_record_offset_; }
|
|
|
|
void Reader::ReportCorruption(uint64_t bytes, const char* reason) {
|
|
ReportDrop(bytes, Status::Corruption(reason));
|
|
}
|
|
|
|
void Reader::ReportDrop(uint64_t bytes, const Status& reason) {
|
|
if (reporter_ != nullptr &&
|
|
end_of_buffer_offset_ - buffer_.size() - bytes >= initial_offset_) {
|
|
reporter_->Corruption(static_cast<size_t>(bytes), reason);
|
|
}
|
|
}
|
|
|
|
unsigned int Reader::ReadPhysicalRecord(Slice* result) {
|
|
while (true) {
|
|
if (buffer_.size() < kHeaderSize) {
|
|
if (!eof_) {
|
|
// Last read was a full read, so this is a trailer to skip
|
|
buffer_.clear();
|
|
Status status = file_->Read(kBlockSize, &buffer_, backing_store_);
|
|
end_of_buffer_offset_ += buffer_.size();
|
|
if (!status.ok()) {
|
|
buffer_.clear();
|
|
ReportDrop(kBlockSize, status);
|
|
eof_ = true;
|
|
return kEof;
|
|
} else if (buffer_.size() < kBlockSize) {
|
|
eof_ = true;
|
|
}
|
|
continue;
|
|
} else {
|
|
// Note that if buffer_ is non-empty, we have a truncated header at the
|
|
// end of the file, which can be caused by the writer crashing in the
|
|
// middle of writing the header. Instead of considering this an error,
|
|
// just report EOF.
|
|
buffer_.clear();
|
|
return kEof;
|
|
}
|
|
}
|
|
|
|
// Parse the header
|
|
const char* header = buffer_.data();
|
|
const uint32_t a = static_cast<uint32_t>(header[4]) & 0xff;
|
|
const uint32_t b = static_cast<uint32_t>(header[5]) & 0xff;
|
|
const unsigned int type = header[6];
|
|
const uint32_t length = a | (b << 8);
|
|
if (kHeaderSize + length > buffer_.size()) {
|
|
size_t drop_size = buffer_.size();
|
|
buffer_.clear();
|
|
if (!eof_) {
|
|
ReportCorruption(drop_size, "bad record length");
|
|
return kBadRecord;
|
|
}
|
|
// If the end of the file has been reached without reading |length| bytes
|
|
// of payload, assume the writer died in the middle of writing the record.
|
|
// Don't report a corruption.
|
|
return kEof;
|
|
}
|
|
|
|
if (type == kZeroType && length == 0) {
|
|
// Skip zero length record without reporting any drops since
|
|
// such records are produced by the mmap based writing code in
|
|
// env_posix.cc that preallocates file regions.
|
|
buffer_.clear();
|
|
return kBadRecord;
|
|
}
|
|
|
|
// Check crc
|
|
if (checksum_) {
|
|
uint32_t expected_crc = crc32c::Unmask(DecodeFixed32(header));
|
|
uint32_t actual_crc = crc32c::Value(header + 6, 1 + length);
|
|
if (actual_crc != expected_crc) {
|
|
// Drop the rest of the buffer since "length" itself may have
|
|
// been corrupted and if we trust it, we could find some
|
|
// fragment of a real log record that just happens to look
|
|
// like a valid log record.
|
|
size_t drop_size = buffer_.size();
|
|
buffer_.clear();
|
|
ReportCorruption(drop_size, "checksum mismatch");
|
|
return kBadRecord;
|
|
}
|
|
}
|
|
|
|
buffer_.remove_prefix(kHeaderSize + length);
|
|
|
|
// Skip physical record that started before initial_offset_
|
|
if (end_of_buffer_offset_ - buffer_.size() - kHeaderSize - length <
|
|
initial_offset_) {
|
|
result->clear();
|
|
return kBadRecord;
|
|
}
|
|
|
|
*result = Slice(header + kHeaderSize, length);
|
|
return type;
|
|
}
|
|
}
|
|
|
|
} // namespace log
|
|
} // namespace leveldb
|