log_reader: introduce kBadHeader; drop wal mode from ReadPhysicalRecord

Move the WAL recovery mode logic out of ReadPhysicalRecord.  To do this we
introduce a new type indicating when we fail to read a valid header.

Signed-off-by: Sage Weil <sage@redhat.com>

db/log_reader.cc

@@ -91,8 +91,8 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch,
   Slice fragment;
   while (true) {
     uint64_t physical_record_offset = end_of_buffer_offset_ - buffer_.size();
-    const unsigned int record_type =
-        ReadPhysicalRecord(&fragment, wal_recovery_mode);
+    size_t drop_size;
+    const unsigned int record_type = ReadPhysicalRecord(&fragment, &drop_size);
     switch (record_type) {
       case kFullType:
         if (in_fragmented_record && !scratch->empty()) {
@@ -142,6 +142,13 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch,
         }
         break;
 
+      case kBadHeader:
+        if (wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
+          // in clean shutdown we don't expect any error in the log files
+          ReportCorruption(drop_size, "truncated header");
+        }
+      // fall-thru
+
       case kEof:
         if (in_fragmented_record) {
           if (wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
@@ -256,8 +263,7 @@ void Reader::ReportDrop(size_t bytes, const Status& reason) {
   }
 }
 
-unsigned int Reader::ReadPhysicalRecord(Slice* result,
-                                        WALRecoveryMode wal_recovery_mode) {
+unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
   while (true) {
     if (buffer_.size() < (size_t)kHeaderSize) {
       if (!eof_ && !read_error_) {
@@ -280,10 +286,10 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result,
         //  end of the file, which can be caused by the writer crashing in the
         //  middle of writing the header. Unless explicitly requested we don't
         //  considering this an error, just report EOF.
-        if (buffer_.size() &&
-            wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
-          // in clean shutdown we don't expect any error in the log files
-          ReportCorruption(buffer_.size(), "truncated header");
+        if (buffer_.size()) {
+          *drop_size = buffer_.size();
+          buffer_.clear();
+          return kBadHeader;
         }
         buffer_.clear();
         return kEof;
@@ -297,19 +303,17 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result,
     const unsigned int type = header[6];
     const uint32_t length = a | (b << 8);
     if (kHeaderSize + length > buffer_.size()) {
-      size_t drop_size = buffer_.size();
+      *drop_size = buffer_.size();
       buffer_.clear();
       if (!eof_) {
-        ReportCorruption(drop_size, "bad record length");
+        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 unless requested.
-      if (drop_size &&
-          wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
-        // in clean shutdown we don't expect any error in the log files
-        ReportCorruption(drop_size, "truncated header");
+      if (*drop_size) {
+        return kBadHeader;
       }
       return kEof;
     }
@@ -333,9 +337,9 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result,
         // 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();
+        *drop_size = buffer_.size();
         buffer_.clear();
-        ReportCorruption(drop_size, "checksum mismatch");
+        ReportCorruption(*drop_size, "checksum mismatch");
         return kBadRecord;
       }
     }

db/log_reader.h

@@ -121,7 +121,9 @@ class Reader {
     // * The record has an invalid CRC (ReadPhysicalRecord reports a drop)
     // * The record is a 0-length record (No drop is reported)
     // * The record is below constructor's initial_offset (No drop is reported)
-    kBadRecord = kMaxRecordType + 2
+    kBadRecord = kMaxRecordType + 2,
+    // Returned when we fail to read a valid header.
+    kBadHeader = kMaxRecordType + 3,
   };
 
   // Skips all blocks that are completely before "initial_offset_".
@@ -130,9 +132,7 @@ class Reader {
   bool SkipToInitialBlock();
 
   // Return type, or one of the preceding special values
-  unsigned int ReadPhysicalRecord(
-      Slice* result, WALRecoveryMode wal_recovery_mode =
-                         WALRecoveryMode::kTolerateCorruptedTailRecords);
+  unsigned int ReadPhysicalRecord(Slice* result, size_t* drop_size);
 
   // Reports dropped bytes to the reporter.
   // buffer_ must be updated to remove the dropped bytes prior to invocation.