// Copyright 2015 The Chromium OS Authors. All rights reserved.
|
// Use of this source code is governed by a BSD-style license that can be
|
// found in the LICENSE file.
|
|
#ifndef _BSDIFF_EXTENTS_FILE_H_
|
#define _BSDIFF_EXTENTS_FILE_H_
|
|
#include <stddef.h>
|
#include <stdint.h>
|
|
#include <memory>
|
#include <vector>
|
|
#include "bsdiff/file_interface.h"
|
|
/*
|
* Extent files.
|
*
|
* This modules provides a familiar interface for handling files through an
|
* indirection layer of extents, which are contiguous chunks of variable length
|
* at arbitrary offsets within a file. Once an extent file handle is obtained,
|
* users may read, write and seek as they do with ordinary files, having the I/O
|
* with the underlying file done for them by the extent file implementation. The
|
* implementation supports "sparse extents", which are assumed to contain zeros
|
* but otherwise have no actual representation in the underlying file; these are
|
* denoted by negative offset values.
|
*
|
* Unlike ordinary files, the size of an extent file is fixed; it is not
|
* truncated on open, nor is writing past the extent span allowed. Also, writing
|
* to a sparse extent has no effect and will not raise an error.
|
*/
|
|
namespace bsdiff {
|
|
/* An extent, defined by an offset and a length. */
|
struct BSDIFF_EXPORT ex_t {
|
off_t off; // the extent offset; negative indicates a sparse extent.
|
uint64_t len; // the extent length.
|
};
|
|
class BSDIFF_EXPORT ExtentsFile : public FileInterface {
|
public:
|
// Creates an ExtentsFile based on the underlying |file| passed. The positions
|
// in the ExtentsFile will be linearly mapped to the extents provided in
|
// |extents|. The created ExtentsFile takes ownership of the |file| will close
|
// it on destruction.
|
ExtentsFile(std::unique_ptr<FileInterface> file,
|
const std::vector<ex_t>& extents);
|
|
~ExtentsFile() override;
|
|
// FileInterface overrides.
|
bool Read(void* buf, size_t count, size_t* bytes_read) override;
|
bool Write(const void* buf, size_t count, size_t* bytes_written) override;
|
bool Seek(off_t pos) override;
|
bool Close() override;
|
bool GetSize(uint64_t* size) override;
|
|
private:
|
void AdvancePos(uint64_t size);
|
|
// Performs an I/O operation (either read or write). This template shares the
|
// code for both Read() and Write() implementations.
|
template <typename T>
|
bool IOOperation(bool (FileInterface::*io_op)(T*, size_t, size_t*),
|
T* buf,
|
size_t count,
|
size_t* bytes_processed);
|
|
// The underlying FileInterace instance.
|
std::unique_ptr<FileInterface> file_;
|
|
// The list of extents mapping this instance to |file_|.
|
const std::vector<ex_t> extents_;
|
|
// The accumulated length of the extents. The i-th element contains the sum of
|
// the length of all the extents from 0 up to but not including the i-th
|
// extent. This reduces the complexity for random-access Seek() calls.
|
std::vector<uint64_t> acc_len_;
|
|
// Current extent index.
|
size_t curr_ex_idx_{0};
|
|
// Current logical file position.
|
uint64_t curr_pos_{0};
|
|
// Total length of all extents (constant).
|
uint64_t total_ex_len_{0};
|
};
|
|
} // namespace bsdiff
|
|
#endif // _BSDIFF_EXTENTS_FILE_H_
|
