Refactor to represent files with a generic header in a new class.

Also move DIRECT I/O alignment setting to a common place.

22 files changed, 216 insertions, 157 deletions

diff --git a/searchlib/src/tests/attribute/enumeratedsave/enumeratedsave_test.cpp b/searchlib/src/tests/attribute/enumeratedsave/enumeratedsave_test.cpp
index dadf3f21297..c67242ee35a 100644
--- a/searchlib/src/tests/attribute/enumeratedsave/enumeratedsave_test.cpp
+++ b/searchlib/src/tests/attribute/enumeratedsave/enumeratedsave_test.cpp
@@ -10,16 +10,17 @@
 #include <vespa/searchlib/attribute/attributememorysavetarget.h>
 #include <vespa/searchlib/attribute/attributesaver.h>
 #include <vespa/searchlib/attribute/i_enum_store_dictionary.h>
-#include <vespa/searchlib/queryeval/executeinfo.h>
 #include <vespa/searchlib/fef/termfieldmatchdata.h>
 #include <vespa/searchlib/index/dummyfileheadercontext.h>
 #include <vespa/searchlib/parsequery/parse.h>
+#include <vespa/searchlib/queryeval/executeinfo.h>
+#include <vespa/searchlib/util/bufferwriter.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/searchlib/util/randomgenerator.h>
+#include <vespa/vespalib/data/databuffer.h>
 #include <vespa/vespalib/testkit/testapp.h>
-#include <vespa/searchlib/util/bufferwriter.h>
 #include <vespa/vespalib/util/compress.h>
 #include <vespa/vespalib/util/size_literals.h>
-#include <vespa/vespalib/data/databuffer.h>
 
 #include <limits>
 #include <iostream>
@@ -57,7 +58,7 @@ public:
     }
 
     virtual Buffer allocBuf(size_t size) override {
-        return std::make_unique<BufferBuf>(size, 4_Ki);
+        return std::make_unique<BufferBuf>(size, search::FileSettings::DIRECTIO_ALIGNMENT);
     }
 
     virtual void writeBuf(Buffer buf_in) override {
diff --git a/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp b/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp
index 13300fb47f2..85d41bce45a 100644
--- a/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp
@@ -1,14 +1,15 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
-#include "attributefilewriter.h"
-#include "attributefilebufferwriter.h"
 #include "attribute_header.h"
-#include <vespa/vespalib/data/fileheader.h>
+#include "attributefilebufferwriter.h"
+#include "attributefilewriter.h"
+#include <vespa/fastos/file.h>
 #include <vespa/searchlib/common/fileheadercontext.h>
 #include <vespa/searchlib/common/tunefileinfo.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/databuffer.h>
+#include <vespa/vespalib/data/fileheader.h>
 #include <vespa/vespalib/util/size_literals.h>
-#include <vespa/fastos/file.h>
 
 #include <vespa/log/log.h>
 LOG_SETUP(".searchlib.attribute.attributefilewriter");
@@ -20,15 +21,12 @@ namespace search {
 
 namespace {
 
-const uint32_t headerAlign = 4_Ki;
-const uint32_t MIN_ALIGNMENT = 4_Ki;
-
 void
 writeDirectIOAligned(FastOS_FileInterface &file, const void *buf, size_t length)
 {
     const char * data(static_cast<const char *>(buf));
     size_t remaining(length);
-    for (size_t maxChunk(2_Mi); maxChunk >= MIN_ALIGNMENT; maxChunk >>= 1) {
+    for (size_t maxChunk(2_Mi); maxChunk >= FileSettings::DIRECTIO_ALIGNMENT; maxChunk >>= 1) {
         for ( ; remaining > maxChunk; remaining -= maxChunk, data += maxChunk) {
             file.WriteBuf(data, maxChunk);
         }
@@ -41,7 +39,7 @@ writeDirectIOAligned(FastOS_FileInterface &file, const void *buf, size_t length)
 void
 updateHeader(const vespalib::string &name, uint64_t fileBitSize)
 {
-    vespalib::FileHeader h(headerAlign);
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     FastOS_File f;
     f.OpenReadWrite(name.c_str());
     h.readFile(f);
@@ -122,11 +120,11 @@ AttributeFileWriter::open(const vespalib::string &fileName)
 void
 AttributeFileWriter::writeHeader()
 {
-    vespalib::FileHeader header(headerAlign);
+    vespalib::FileHeader header(FileSettings::DIRECTIO_ALIGNMENT);
     _fileHeaderContext.addTags(header, _file->GetFileName());
     addTags(header);
     size_t headerLen = header.writeFile(*_file);
-    assert((headerLen % MIN_ALIGNMENT) == 0);
+    assert((headerLen % FileSettings::DIRECTIO_ALIGNMENT) == 0);
     _fileBitSize = headerLen * 8;
 }
 
@@ -141,7 +139,7 @@ AttributeFileWriter::addTags(vespalib::GenericHeader &header)
 AttributeFileWriter::Buffer
 AttributeFileWriter::allocBuf(size_t size)
 {
-    return std::make_unique<BufferBuf>(size, MIN_ALIGNMENT);
+    return std::make_unique<BufferBuf>(size, FileSettings::DIRECTIO_ALIGNMENT);
 }
 
 void
diff --git a/searchlib/src/vespa/searchlib/attribute/attributememoryfilewriter.cpp b/searchlib/src/vespa/searchlib/attribute/attributememoryfilewriter.cpp
index 7662df9443e..5522229b8c9 100644
--- a/searchlib/src/vespa/searchlib/attribute/attributememoryfilewriter.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/attributememoryfilewriter.cpp
@@ -1,18 +1,13 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
-#include "attributememoryfilewriter.h"
 #include "attributememoryfilebufferwriter.h"
+#include "attributememoryfilewriter.h"
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/databuffer.h>
 #include <vespa/vespalib/util/size_literals.h>
 
 namespace search {
 
-namespace {
-
-const uint32_t MIN_ALIGNMENT = 4_Ki;
-
-}
-
 AttributeMemoryFileWriter::AttributeMemoryFileWriter()
     : IAttributeFileWriter(),
       _bufs()
@@ -26,7 +21,7 @@ AttributeMemoryFileWriter::~AttributeMemoryFileWriter() = default;
 AttributeMemoryFileWriter::Buffer
 AttributeMemoryFileWriter::allocBuf(size_t size)
 {
-    return std::make_unique<BufferBuf>(size, MIN_ALIGNMENT);
+    return std::make_unique<BufferBuf>(size, FileSettings::DIRECTIO_ALIGNMENT);
 }
 
 
diff --git a/searchlib/src/vespa/searchlib/attribute/attributevector.cpp b/searchlib/src/vespa/searchlib/attribute/attributevector.cpp
index 5de342bf380..10a4d8addc2 100644
--- a/searchlib/src/vespa/searchlib/attribute/attributevector.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/attributevector.cpp
@@ -20,6 +20,7 @@
 #include <vespa/searchlib/index/dummyfileheadercontext.h>
 #include <vespa/searchlib/query/query_term_decoder.h>
 #include <vespa/searchlib/queryeval/emptysearch.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/searchlib/util/logutil.h>
 #include <vespa/vespalib/util/exceptions.h>
 #include <vespa/vespalib/util/size_literals.h>
@@ -47,8 +48,6 @@ const vespalib::string dataTypeTag = "datatype";
 const vespalib::string collectionTypeTag = "collectiontype";
 const vespalib::string docIdLimitTag = "docIdLimit";
 
-constexpr size_t DIRECTIO_ALIGNMENT(4_Ki);
-
 }
 
 namespace search {
@@ -351,7 +350,7 @@ AttributeVector::isEnumeratedSaveFormat() const
 {
     vespalib::string datName(vespalib::make_string("%s.dat", getBaseFileName().c_str()));
     Fast_BufferedFile   datFile;
-    vespalib::FileHeader datHeader(DIRECTIO_ALIGNMENT);
+    vespalib::FileHeader datHeader(FileSettings::DIRECTIO_ALIGNMENT);
     if ( ! datFile.OpenReadOnly(datName.c_str()) ) {
         LOG(error, "could not open %s: %s", datFile.GetFileName(), getLastErrorString().c_str());
         throw IllegalStateException(make_string("Failed opening attribute data file '%s' for reading",
@@ -648,7 +647,7 @@ IExtendAttribute *AttributeVector::getExtendInterface() { return nullptr; }
 uint64_t
 AttributeVector::getEstimatedSaveByteSize() const
 {
-    uint64_t headerSize = 4_Ki;
+    uint64_t headerSize = FileSettings::DIRECTIO_ALIGNMENT;
     uint64_t totalValueCount = _status.getNumValues();
     uint64_t uniqueValueCount = _status.getNumUniqueValues();
     uint64_t docIdLimit = getCommittedDocIdLimit();
diff --git a/searchlib/src/vespa/searchlib/attribute/primitivereader.h b/searchlib/src/vespa/searchlib/attribute/primitivereader.h
index cf8821526d0..0499138bc49 100644
--- a/searchlib/src/vespa/searchlib/attribute/primitivereader.h
+++ b/searchlib/src/vespa/searchlib/attribute/primitivereader.h
@@ -13,7 +13,7 @@ namespace search {
     public:
         PrimitiveReader(AttributeVector &attr)
             : ReaderBase(attr),
-              _datReader(*_datFile)
+              _datReader(_datFile.file())
         { }
 
         virtual ~PrimitiveReader() { }
diff --git a/searchlib/src/vespa/searchlib/attribute/readerbase.cpp b/searchlib/src/vespa/searchlib/attribute/readerbase.cpp
index b55ba221a42..33cec01fb0a 100644
--- a/searchlib/src/vespa/searchlib/attribute/readerbase.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/readerbase.cpp
@@ -19,8 +19,6 @@ const vespalib::string versionTag = "version";
 const vespalib::string docIdLimitTag = "docIdLimit";
 const vespalib::string createSerialNumTag = "createSerialNum";
 
-constexpr size_t DIRECTIO_ALIGNMENT(4_Ki);
-
 uint64_t
 extractCreateSerialNum(const vespalib::GenericHeader &header)
 {
@@ -35,53 +33,38 @@ ReaderBase::ReaderBase(AttributeVector &attr)
                   attribute::LoadUtils::openWeight(attr) : std::unique_ptr<Fast_BufferedFile>()),
       _idxFile(attr.hasMultiValue() ?
                attribute::LoadUtils::openIDX(attr) : std::unique_ptr<Fast_BufferedFile>()),
-      _weightReader(*_weightFile),
-      _idxReader(*_idxFile),
-      _enumReader(*_datFile),
+      _weightReader(_weightFile.file()),
+      _idxReader(_idxFile.file()),
+      _enumReader(_datFile.file()),
       _currIdx(0),
-      _datHeaderLen(0u),
-      _idxHeaderLen(0u),
-      _weightHeaderLen(0u),
       _createSerialNum(0u),
       _fixedWidth(attr.getFixedWidth()),
       _enumerated(false),
       _hasLoadData(false),
       _version(0),
-      _docIdLimit(0),
-      _datHeader(DIRECTIO_ALIGNMENT),
-      _datFileSize(0),
-      _idxFileSize(0)
+      _docIdLimit(0)
 {
-    _datHeaderLen = _datHeader.readFile(*_datFile);
-    _datFile->SetPosition(_datHeaderLen);
-    if (!attr.headerTypeOK(_datHeader) ||
-        !extractFileSize(_datHeader, *_datFile, _datFileSize)) {
-        _datFile->Close();
+    if (!attr.headerTypeOK(_datFile.header())) {
+        _datFile.close();
     }
-    _createSerialNum = extractCreateSerialNum(_datHeader);
-    if (_datHeader.hasTag(versionTag)) {
-        _version = _datHeader.getTag(versionTag).asInteger();
+    _createSerialNum = extractCreateSerialNum(_datFile.header());
+    if (_datFile.header().hasTag(versionTag)) {
+        _version = _datFile.header().getTag(versionTag).asInteger();
     }
-    _docIdLimit = _datHeader.getTag(docIdLimitTag).asInteger();
+    _docIdLimit = _datFile.header().getTag(docIdLimitTag).asInteger();
     if (hasIdx()) {
-        vespalib::FileHeader idxHeader(DIRECTIO_ALIGNMENT);
-        _idxHeaderLen = idxHeader.readFile(*_idxFile);
-        _idxFile->SetPosition(_idxHeaderLen);
-        if (!attr.headerTypeOK(idxHeader) ||
-            !extractFileSize(idxHeader, *_idxFile, _idxFileSize)) {
-            _idxFile->Close();
+        if (!attr.headerTypeOK(_idxFile.header())) {
+            _idxFile.close();
         } else  {
             _currIdx = _idxReader.readHostOrder();
         }
     }
     if (hasWeight()) {
-        vespalib::FileHeader weightHeader(DIRECTIO_ALIGNMENT);
-        _weightHeaderLen = weightHeader.readFile(*_weightFile);
-        _weightFile->SetPosition(_weightHeaderLen);
-        if (!attr.headerTypeOK(weightHeader))
-            _weightFile->Close();
+        if (!attr.headerTypeOK(_weightFile.header())) {
+            _weightFile.close();
+        }
     }
-    if (hasData() && AttributeVector::isEnumerated(_datHeader)) {
+    if (hasData() && AttributeVector::isEnumerated(_datFile.header())) {
         _enumerated = true;
     }
     _hasLoadData = hasData() &&
@@ -93,40 +76,30 @@ ReaderBase::~ReaderBase() = default;
 
 bool
 ReaderBase::hasWeight() const {
-    return _weightFile.get() && _weightFile->IsOpened();
+    return _weightFile.valid();
 }
 
 bool
 ReaderBase::hasIdx() const {
-    return _idxFile.get() && _idxFile->IsOpened();
+    return _idxFile.valid();
 }
 
 bool
 ReaderBase::hasData() const {
-    return _datFile.get() && _datFile->IsOpened();
-}
-
-bool
-ReaderBase::
-extractFileSize(const vespalib::GenericHeader &header,
-                FastOS_FileInterface &file, uint64_t &fileSize)
-{
-    fileSize = file.GetSize();
-    return FileSizeCalculator::extractFileSize(header, header.getSize(),
-                                               file.GetFileName(), fileSize);
+    return _datFile.valid();
 }
 
 void
 ReaderBase::rewind()
 {
-    _datFile->SetPosition(_datHeaderLen);
+    _datFile.rewind();
     _currIdx = 0;
     if (hasIdx()) {
-        _idxFile->SetPosition(_idxHeaderLen);
+        _idxFile.rewind();
         _currIdx = _idxReader.readHostOrder();
     }
     if (hasWeight()) {
-        _weightFile->SetPosition(_weightHeaderLen);
+        _weightFile.rewind();
     }
 }
 
@@ -137,13 +110,13 @@ ReaderBase::getNumValues()
        return getEnumCount();
     } else {
        if (_fixedWidth > 0) {
-           size_t dataSize(_datFileSize - _datHeaderLen);
+           size_t dataSize = _datFile.data_size();
            assert((dataSize % _fixedWidth) == 0);
            return dataSize / _fixedWidth;
         } else {
             // TODO. This limits the number of multivalues to 2^32-1
             // This is assert during write, so this should never be a problem here.
-            _idxFile->SetPosition(_idxFileSize - 4);
+            _idxFile.file().SetPosition(_idxFile.file_size() - 4);
             size_t numValues = _idxReader.readHostOrder();
             rewind();
             return numValues;
diff --git a/searchlib/src/vespa/searchlib/attribute/readerbase.h b/searchlib/src/vespa/searchlib/attribute/readerbase.h
index a7685e4532a..c439fb81738 100644
--- a/searchlib/src/vespa/searchlib/attribute/readerbase.h
+++ b/searchlib/src/vespa/searchlib/attribute/readerbase.h
@@ -2,6 +2,7 @@
 
 #pragma once
 
+#include <vespa/searchlib/util/file_with_header.h>
 #include <vespa/searchlib/util/fileutil.h>
 #include <cassert>
 
@@ -21,18 +22,15 @@ public:
     bool hasData() const;
 
     uint32_t getNumIdx() const {
-        return (_idxFileSize - _idxHeaderLen) /sizeof(uint32_t);
+        return (_idxFile.data_size()) /sizeof(uint32_t);
     }
 
     size_t getEnumCount() const {
-        size_t dataSize(_datFileSize - _datHeaderLen);
+        size_t dataSize = _datFile.data_size();
         assert((dataSize % sizeof(uint32_t)) == 0);
         return dataSize / sizeof(uint32_t);
     }
 
-    static bool
-    extractFileSize(const vespalib::GenericHeader &header, FastOS_FileInterface &file, uint64_t &fileSize);
-
     size_t getNumValues();
     int32_t getNextWeight() { return _weightReader.readHostOrder(); }
     uint32_t getNextEnum() { return _enumReader.readHostOrder(); }
@@ -43,32 +41,26 @@ public:
     uint32_t getVersion() const { return _version; }
     uint32_t getDocIdLimit() const { return _docIdLimit; }
     const vespalib::GenericHeader &getDatHeader() const {
-        return _datHeader;
+        return _datFile.header();
     }
 protected:
-    std::unique_ptr<FastOS_FileInterface>  _datFile;
+    FileWithHeader _datFile;
 private:
-    std::unique_ptr<FastOS_FileInterface>  _weightFile;
-    std::unique_ptr<FastOS_FileInterface>  _idxFile;
+    FileWithHeader        _weightFile;
+    FileWithHeader        _idxFile;
     FileReader<int32_t>   _weightReader;
     FileReader<uint32_t>  _idxReader;
     FileReader<uint32_t>  _enumReader;
     uint32_t              _currIdx;
-    uint32_t              _datHeaderLen;
-    uint32_t              _idxHeaderLen;
-    uint32_t              _weightHeaderLen;
     uint64_t              _createSerialNum;
     size_t                _fixedWidth;
     bool                  _enumerated;
     bool                  _hasLoadData;
     uint32_t              _version;
     uint32_t              _docIdLimit;
-    vespalib::FileHeader  _datHeader;
-    uint64_t              _datFileSize;
-    uint64_t              _idxFileSize;
 protected:
     size_t getDataCountHelper(size_t elemSize) const {
-        size_t dataSize(_datFileSize - _datHeaderLen);
+        size_t dataSize = _datFile.data_size();
         return dataSize / elemSize;
     }
 };
diff --git a/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp b/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp
index 42bc8438d8c..42418c736bf 100644
--- a/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp
@@ -1,13 +1,14 @@
 // Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
-#include "singleboolattribute.h"
 #include "attributevector.hpp"
-#include "primitivereader.h"
 #include "iattributesavetarget.h"
 #include "ipostinglistsearchcontext.h"
+#include "primitivereader.h"
+#include "singleboolattribute.h"
+#include <vespa/searchlib/common/bitvectoriterator.h>
 #include <vespa/searchlib/query/query_term_simple.h>
 #include <vespa/searchlib/queryeval/emptysearch.h>
-#include <vespa/searchlib/common/bitvectoriterator.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/databuffer.h>
 #include <vespa/vespalib/util/size_literals.h>
 
@@ -245,7 +246,7 @@ SingleBoolAttribute::onShrinkLidSpace()
 uint64_t
 SingleBoolAttribute::getEstimatedSaveByteSize() const
 {
-    constexpr uint64_t headerSize = 4_Ki + sizeof(uint32_t);
+    constexpr uint64_t headerSize = FileSettings::DIRECTIO_ALIGNMENT + sizeof(uint32_t);
     return headerSize + _bv.sizeBytes();
 }
 
diff --git a/searchlib/src/vespa/searchlib/attribute/singlenumericattributesaver.cpp b/searchlib/src/vespa/searchlib/attribute/singlenumericattributesaver.cpp
index 92e25097f40..359da48fb59 100644
--- a/searchlib/src/vespa/searchlib/attribute/singlenumericattributesaver.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/singlenumericattributesaver.cpp
@@ -1,7 +1,8 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
-#include "singlenumericattributesaver.h"
 #include "iattributesavetarget.h"
+#include "singlenumericattributesaver.h"
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/databuffer.h>
 #include <vespa/vespalib/util/size_literals.h>
 
@@ -9,20 +10,13 @@ using vespalib::GenerationHandler;
 
 namespace search {
 
-namespace {
-
-const uint32_t MIN_ALIGNMENT = 4_Ki;
-
-}
-
-
 SingleValueNumericAttributeSaver::
 SingleValueNumericAttributeSaver(const attribute::AttributeHeader &header,
                                  const void *data, size_t size)
   : AttributeSaver(vespalib::GenerationHandler::Guard(), header),
     _buf()
 {
-    _buf = std::make_unique<BufferBuf>(size, MIN_ALIGNMENT);
+    _buf = std::make_unique<BufferBuf>(size, FileSettings::DIRECTIO_ALIGNMENT);
     assert(_buf->getFreeLen() >= size);
     if (size > 0) {
         memcpy(_buf->getFree(), data, size);
@@ -31,11 +25,8 @@ SingleValueNumericAttributeSaver(const attribute::AttributeHeader &header,
     assert(_buf->getDataLen() == size);
 }
 
-
 SingleValueNumericAttributeSaver::~SingleValueNumericAttributeSaver() = default;
 
-
-
 bool
 SingleValueNumericAttributeSaver::onSave(IAttributeSaveTarget &saveTarget)
 {
@@ -43,5 +34,4 @@ SingleValueNumericAttributeSaver::onSave(IAttributeSaveTarget &saveTarget)
     return true;
 }
 
-
 }  // namespace search
diff --git a/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp b/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp
index cdcc70cc01d..72aadbc6d93 100644
--- a/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp
@@ -1,12 +1,13 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
-#include "singlesmallnumericattribute.h"
-#include "attributevector.hpp"
-#include "primitivereader.h"
 #include "attributeiterators.hpp"
+#include "attributevector.hpp"
 #include "iattributesavetarget.h"
+#include "primitivereader.h"
+#include "singlesmallnumericattribute.h"
 #include <vespa/searchlib/query/query_term_simple.h>
 #include <vespa/searchlib/queryeval/emptysearch.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/databuffer.h>
 #include <vespa/vespalib/util/size_literals.h>
 
@@ -200,7 +201,7 @@ SingleValueSmallNumericAttribute::onShrinkLidSpace()
 uint64_t
 SingleValueSmallNumericAttribute::getEstimatedSaveByteSize() const
 {
-    uint64_t headerSize = 4_Ki;
+    uint64_t headerSize = FileSettings::DIRECTIO_ALIGNMENT;
     const size_t numDocs(getCommittedDocIdLimit());
     const size_t numDataWords((numDocs + _valueShiftMask) >> _wordShift);
     const size_t sz((numDataWords + 1) * sizeof(Word));
diff --git a/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp b/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp
index 8c1cbc3d672..7f5ae051978 100644
--- a/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp
@@ -3,6 +3,7 @@
 #include "sourceselector.h"
 #include <vespa/fastlib/io/bufferedfile.h>
 #include <vespa/searchlib/common/fileheadercontext.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/util/size_literals.h>
 
 using search::queryeval::Source;
@@ -83,7 +84,7 @@ SourceSelector::LoadInfo::load()
     // XXX no checking for success
     file.ReadOpen(fileName.c_str());
 
-    FileHeader fileHeader(4_Ki);
+    FileHeader fileHeader(FileSettings::DIRECTIO_ALIGNMENT);
     fileHeader.readFile(file);
     if (fileHeader.hasTag(defaultSourceTag)) {
         _header._defaultSource = fileHeader.getTag(defaultSourceTag).asInteger();
diff --git a/searchlib/src/vespa/searchlib/common/bitvector.cpp b/searchlib/src/vespa/searchlib/common/bitvector.cpp
index 97edece249e..6f551222286 100644
--- a/searchlib/src/vespa/searchlib/common/bitvector.cpp
+++ b/searchlib/src/vespa/searchlib/common/bitvector.cpp
@@ -4,6 +4,7 @@
 #include "allocatedbitvector.h"
 #include "growablebitvector.h"
 #include "partialbitvector.h"
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/hwaccelrated/iaccelrated.h>
 #include <vespa/vespalib/util/exceptions.h>
 #include <vespa/vespalib/util/size_literals.h>
@@ -34,7 +35,6 @@ void verifyInclusiveStart(const search::BitVector & a, const search::BitVector &
 }
 
 constexpr size_t MMAP_LIMIT = 256_Mi;
-constexpr size_t DIRECTIO_ALIGNMENT = 4_Ki;
 
 }
 
@@ -341,7 +341,8 @@ BitVector::create(Index numberOfElements, FastOS_FileInterface &file,
         size_t vectorsize = getFileBytes(numberOfElements);
         file.DirectIOPadding(offset, vectorsize, padbefore, padafter);
         assert((padbefore & (getAlignment() - 1)) == 0);
-        AllocatedBitVector::Alloc alloc = Alloc::alloc(padbefore + vectorsize + padafter, MMAP_LIMIT, DIRECTIO_ALIGNMENT);
+        AllocatedBitVector::Alloc alloc = Alloc::alloc(padbefore + vectorsize + padafter,
+                                                       MMAP_LIMIT, FileSettings::DIRECTIO_ALIGNMENT);
         void * alignedBuffer = alloc.get();
         file.ReadBuf(alignedBuffer, alloc.size(), offset - padbefore);
         bv = std::make_unique<AllocatedBitVector>(numberOfElements, std::move(alloc), padbefore);
diff --git a/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp b/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp
index 828e38b5267..2e4218ed36c 100644
--- a/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp
@@ -1,9 +1,10 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
 #include "bitvectorfile.h"
-#include <vespa/searchlib/index/bitvectorkeys.h>
 #include <vespa/searchlib/common/bitvector.h>
 #include <vespa/searchlib/common/fileheadercontext.h>
+#include <vespa/searchlib/index/bitvectorkeys.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/fileheader.h>
 #include <vespa/vespalib/util/size_literals.h>
 #include <cassert>
@@ -25,8 +26,6 @@ readHeader(vespalib::FileHeader &h,
     file.Close();
 }
 
-const size_t FILE_HEADERSIZE_ALIGNMENT = 4_Ki;
-
 }
 
 BitVectorFileWrite::BitVectorFileWrite(BitVectorKeyScope scope)
@@ -93,7 +92,7 @@ BitVectorFileWrite::open(const vespalib::string &name,
 void
 BitVectorFileWrite::makeDatHeader(const FileHeaderContext &fileHeaderContext)
 {
-    vespalib::FileHeader h(FILE_HEADERSIZE_ALIGNMENT); // 64 byte alignment on bitvector.dat header
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     typedef vespalib::GenericHeader::Tag Tag;
     fileHeaderContext.addTags(h, _datFile->GetFileName());
     h.putTag(Tag("docIdLimit", _docIdLimit));
@@ -110,7 +109,7 @@ BitVectorFileWrite::makeDatHeader(const FileHeaderContext &fileHeaderContext)
 void
 BitVectorFileWrite::updateDatHeader(uint64_t fileBitSize)
 {
-    vespalib::FileHeader h(FILE_HEADERSIZE_ALIGNMENT);
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     typedef vespalib::GenericHeader::Tag Tag;
     readHeader(h, _datFile->GetFileName());
     FileHeaderContext::setFreezeTime(h);
diff --git a/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp b/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp
index 95d2b286d7f..176840c4903 100644
--- a/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp
@@ -1,9 +1,10 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
 #include "bitvectoridxfile.h"
-#include <vespa/searchlib/index/bitvectorkeys.h>
 #include <vespa/searchlib/common/bitvector.h>
 #include <vespa/searchlib/common/fileheadercontext.h>
+#include <vespa/searchlib/index/bitvectorkeys.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/fileheader.h>
 #include <vespa/vespalib/util/size_literals.h>
 #include <cassert>
@@ -24,8 +25,6 @@ readHeader(vespalib::FileHeader &h, const vespalib::string &name)
     file.Close();
 }
 
-const size_t FILE_HEADERSIZE_ALIGNMENT = 4_Ki;
-
 }
 
 BitVectorIdxFileWrite::BitVectorIdxFileWrite(BitVectorKeyScope scope)
@@ -90,7 +89,7 @@ BitVectorIdxFileWrite::open(const vespalib::string &name,
 void
 BitVectorIdxFileWrite::makeIdxHeader(const FileHeaderContext &fileHeaderContext)
 {
-    vespalib::FileHeader h(FILE_HEADERSIZE_ALIGNMENT);
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     typedef vespalib::GenericHeader::Tag Tag;
     fileHeaderContext.addTags(h, _idxFile->GetFileName());
     h.putTag(Tag("docIdLimit", _docIdLimit));
@@ -108,7 +107,7 @@ BitVectorIdxFileWrite::makeIdxHeader(const FileHeaderContext &fileHeaderContext)
 void
 BitVectorIdxFileWrite::updateIdxHeader(uint64_t fileBitSize)
 {
-    vespalib::FileHeader h(FILE_HEADERSIZE_ALIGNMENT);
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     typedef vespalib::GenericHeader::Tag Tag;
     readHeader(h, _idxFile->GetFileName());
     FileHeaderContext::setFreezeTime(h);
diff --git a/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp b/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp
index 64fb6142db7..70a67705687 100644
--- a/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp
@@ -2,7 +2,7 @@
 
 #include "pagedict4file.h"
 #include <vespa/searchlib/common/fileheadercontext.h>
-#include <vespa/vespalib/stllike/asciistream.h>
+#include <vespa/searchlib/util/file_settings.h>
 #include <vespa/vespalib/data/fileheader.h>
 #include <vespa/vespalib/io/fileutil.h>
 #include <vespa/vespalib/util/size_literals.h>
@@ -36,12 +36,6 @@ using vespalib::getLastErrorString;
 
 namespace search::diskindex {
 
-namespace {
-
-const uint32_t headerAlign = 4_Ki;
-
-}
-
 PageDict4FileSeqRead::PageDict4FileSeqRead()
     : _pReader(nullptr),
       _ssReader(nullptr),
@@ -467,7 +461,7 @@ PageDict4FileSeqWrite::makePHeader(const FileHeaderContext &fileHeaderContext)
     // subheader only written to SS file.
 
     typedef vespalib::GenericHeader::Tag Tag;
-    vespalib::FileHeader header(headerAlign);
+    vespalib::FileHeader header(FileSettings::DIRECTIO_ALIGNMENT);
 
     fileHeaderContext.addTags(header, _pfile.GetFileName());
     header.putTag(Tag("frozen", 0));
@@ -499,7 +493,7 @@ PageDict4FileSeqWrite::makeSPHeader(const FileHeaderContext &fileHeaderContext)
     // subheader only written to SS file.
 
     typedef vespalib::GenericHeader::Tag Tag;
-    vespalib::FileHeader header(headerAlign);
+    vespalib::FileHeader header(FileSettings::DIRECTIO_ALIGNMENT);
 
     fileHeaderContext.addTags(header, _spfile.GetFileName());
     header.putTag(Tag("frozen", 0));
@@ -529,7 +523,7 @@ PageDict4FileSeqWrite::makeSSHeader(const FileHeaderContext &fileHeaderContext)
     ComprFileWriteContext &wc = _ssWriteContext;
 
     typedef vespalib::GenericHeader::Tag Tag;
-    vespalib::FileHeader header(headerAlign);
+    vespalib::FileHeader header(FileSettings::DIRECTIO_ALIGNMENT);
 
     fileHeaderContext.addTags(header, _ssfile.GetFileName());
     header.putTag(Tag("frozen", 0));
@@ -557,7 +551,7 @@ PageDict4FileSeqWrite::makeSSHeader(const FileHeaderContext &fileHeaderContext)
 void
 PageDict4FileSeqWrite::updatePHeader(uint64_t fileBitSize)
 {
-    vespalib::FileHeader h(headerAlign);
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     FastOS_File f;
     f.OpenReadWrite(_pfile.GetFileName());
     h.readFile(f);
@@ -574,7 +568,7 @@ PageDict4FileSeqWrite::updatePHeader(uint64_t fileBitSize)
 void
 PageDict4FileSeqWrite::updateSPHeader(uint64_t fileBitSize)
 {
-    vespalib::FileHeader h(headerAlign);
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     FastOS_File f;
     f.OpenReadWrite(_spfile.GetFileName());
     h.readFile(f);
@@ -591,7 +585,7 @@ PageDict4FileSeqWrite::updateSPHeader(uint64_t fileBitSize)
 void
 PageDict4FileSeqWrite::updateSSHeader(uint64_t fileBitSize)
 {
-    vespalib::FileHeader h(headerAlign);
+    vespalib::FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     FastOS_File f;
     f.OpenReadWrite(_ssfile.GetFileName());
     h.readFile(f);
diff --git a/searchlib/src/vespa/searchlib/docstore/writeablefilechunk.cpp b/searchlib/src/vespa/searchlib/docstore/writeablefilechunk.cpp
index f498b93ca14..5740092269d 100644
--- a/searchlib/src/vespa/searchlib/docstore/writeablefilechunk.cpp
+++ b/searchlib/src/vespa/searchlib/docstore/writeablefilechunk.cpp
@@ -1,16 +1,17 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
-#include "writeablefilechunk.h"
 #include "data_store_file_chunk_stats.h"
 #include "summaryexceptions.h"
-#include <vespa/vespalib/util/lambdatask.h>
-#include <vespa/vespalib/util/array.hpp>
-#include <vespa/vespalib/util/size_literals.h>
-#include <vespa/vespalib/data/fileheader.h>
-#include <vespa/vespalib/data/databuffer.h>
+#include "writeablefilechunk.h"
 #include <vespa/searchlib/common/fileheadercontext.h>
-#include <vespa/vespalib/stllike/hash_map.hpp>
+#include <vespa/searchlib/util/file_settings.h>
+#include <vespa/vespalib/data/databuffer.h>
+#include <vespa/vespalib/data/fileheader.h>
 #include <vespa/vespalib/objects/nbostream.h>
+#include <vespa/vespalib/stllike/hash_map.hpp>
+#include <vespa/vespalib/util/array.hpp>
+#include <vespa/vespalib/util/lambdatask.h>
+#include <vespa/vespalib/util/size_literals.h>
 
 #include <vespa/log/log.h>
 LOG_SETUP(".search.writeablefilechunk");
@@ -27,8 +28,7 @@ namespace search {
 
 namespace {
 
-const uint64_t Alignment = 4_Ki;
-const uint64_t headerAlign = 4_Ki;
+const size_t Alignment = FileSettings::DIRECTIO_ALIGNMENT;
 
 }
 
@@ -785,7 +785,7 @@ void
 WriteableFileChunk::writeDataHeader(const FileHeaderContext &fileHeaderContext)
 {
     typedef FileHeader::Tag Tag;
-    FileHeader h(headerAlign);
+    FileHeader h(FileSettings::DIRECTIO_ALIGNMENT);
     assert(_dataFile.IsOpened());
     assert(_dataFile.IsWriteMode());
     assert(_dataFile.GetPosition() == 0);
diff --git a/searchlib/src/vespa/searchlib/tensor/blob_sequence_reader.h b/searchlib/src/vespa/searchlib/tensor/blob_sequence_reader.h
index 7c34b60e93d..f96b4e46e98 100644
--- a/searchlib/src/vespa/searchlib/tensor/blob_sequence_reader.h
+++ b/searchlib/src/vespa/searchlib/tensor/blob_sequence_reader.h
@@ -17,10 +17,10 @@ private:
 public:
     BlobSequenceReader(AttributeVector &attr)
         : ReaderBase(attr),
-          _sizeReader(*_datFile)
+          _sizeReader(_datFile.file())
     { }
     uint32_t getNextSize() { return _sizeReader.readHostOrder(); }
-    void readBlob(void *buf, size_t len) { _datFile->ReadBuf(buf, len); }
+    void readBlob(void *buf, size_t len) { _datFile.file().ReadBuf(buf, len); }
 };
 
 } // namespace
diff --git a/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp b/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp
index fd86fbf1c73..00aede95ca4 100644
--- a/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp
+++ b/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp
@@ -43,7 +43,7 @@ public:
     BlobSequenceReader(AttributeVector &attr);
     ~BlobSequenceReader();
     bool is_present();
-    void readTensor(void *buf, size_t len) { _datFile->ReadBuf(buf, len); }
+    void readTensor(void *buf, size_t len) { _datFile.file().ReadBuf(buf, len); }
 };
 
 BlobSequenceReader::BlobSequenceReader(AttributeVector &attr)
@@ -55,7 +55,7 @@ BlobSequenceReader::~BlobSequenceReader() = default;
 bool
 BlobSequenceReader::is_present() {
     unsigned char detect;
-    _datFile->ReadBuf(&detect, sizeof(detect));
+    _datFile.file().ReadBuf(&detect, sizeof(detect));
     if (detect == tensorIsNotPresent) {
         return false;
     }
diff --git a/searchlib/src/vespa/searchlib/util/CMakeLists.txt b/searchlib/src/vespa/searchlib/util/CMakeLists.txt
index 320a6480202..1b311e8d639 100644
--- a/searchlib/src/vespa/searchlib/util/CMakeLists.txt
+++ b/searchlib/src/vespa/searchlib/util/CMakeLists.txt
@@ -6,6 +6,7 @@ vespa_add_library(searchlib_util OBJECT
     comprfile.cpp
     dirtraverse.cpp
     drainingbufferwriter.cpp
+    file_with_header.cpp
     filealign.cpp
     fileheadertk.cpp
     filekit.cpp
diff --git a/searchlib/src/vespa/searchlib/util/file_settings.h b/searchlib/src/vespa/searchlib/util/file_settings.h
new file mode 100644
index 00000000000..1bdd1a56cda
--- /dev/null
+++ b/searchlib/src/vespa/searchlib/util/file_settings.h
@@ -0,0 +1,17 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include <vespa/vespalib/util/size_literals.h>
+
+namespace search {
+
+/**
+ * Common settings that is used for file I/O.
+ */
+struct FileSettings {
+    // The alignment (in bytes) used for DIRECT I/O write and read.
+    static constexpr size_t DIRECTIO_ALIGNMENT = 4_Ki;
+};
+
+}
diff --git a/searchlib/src/vespa/searchlib/util/file_with_header.cpp b/searchlib/src/vespa/searchlib/util/file_with_header.cpp
new file mode 100644
index 00000000000..b004f2b29d5
--- /dev/null
+++ b/searchlib/src/vespa/searchlib/util/file_with_header.cpp
@@ -0,0 +1,59 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#include "file_settings.h"
+#include "file_with_header.h"
+#include "filesizecalculator.h"
+#include <vespa/fastos/file.h>
+#include <vespa/vespalib/util/size_literals.h>
+
+namespace search {
+
+namespace {
+
+bool
+extract_file_size(const vespalib::GenericHeader& header,
+                  FastOS_FileInterface& file, uint64_t& file_size)
+{
+    file_size = file.GetSize();
+    return FileSizeCalculator::extractFileSize(header, header.getSize(),file.GetFileName(), file_size);
+}
+
+}
+
+FileWithHeader::FileWithHeader(std::unique_ptr<FastOS_FileInterface> file_in)
+    : _file(std::move(file_in)),
+      _header(FileSettings::DIRECTIO_ALIGNMENT),
+      _header_len(0),
+      _file_size(0)
+{
+    if (valid()) {
+        _header_len = _header.readFile(*_file);
+        _file->SetPosition(_header_len);
+        if (!extract_file_size(_header, *_file, _file_size)) {
+            _file->Close();
+        }
+    }
+}
+
+FileWithHeader::~FileWithHeader() = default;
+
+bool
+FileWithHeader::valid() const
+{
+    return _file && _file->IsOpened();
+}
+
+void
+FileWithHeader::rewind()
+{
+    _file->SetPosition(_header_len);
+}
+
+void
+FileWithHeader::close()
+{
+    _file->Close();
+}
+
+
+}
diff --git a/searchlib/src/vespa/searchlib/util/file_with_header.h b/searchlib/src/vespa/searchlib/util/file_with_header.h
new file mode 100644
index 00000000000..4432b76be67
--- /dev/null
+++ b/searchlib/src/vespa/searchlib/util/file_with_header.h
@@ -0,0 +1,38 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include <vespa/vespalib/data/fileheader.h>
+#include <memory>
+
+class FastOS_FileInterface;
+
+namespace search {
+
+/**
+ * Class that encapsulates a file containing a generic file header, followed by binary data.
+ *
+ * After construction the file is positioned at the start of the binary data.
+ * It's assumed that the file was written using FileSettings::DIRECTIO_ALIGNMENT.
+ */
+class FileWithHeader {
+private:
+    std::unique_ptr<FastOS_FileInterface> _file;
+    vespalib::FileHeader _header;
+    uint64_t _header_len;
+    uint64_t _file_size;
+
+public:
+    FileWithHeader(std::unique_ptr<FastOS_FileInterface> file_in);
+    ~FileWithHeader();
+    FastOS_FileInterface& file() const { return *_file; }
+    const vespalib::GenericHeader& header() const { return _header; }
+    uint64_t file_size() const { return _file_size; }
+    uint64_t data_size() const { return _file_size - _header_len; }
+
+    bool valid() const;
+    void rewind();
+    void close();
+};
+
+}