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117 lines
3.6 KiB
117 lines
3.6 KiB
// Copyright 2015 The Chromium OS Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "bsdiff/extents_file.h"
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#include <string.h>
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#include <algorithm>
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// Extent files implementation extending FileInterface.
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//
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// This class allows to map linear positions in a file to a list of regions in
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// another file. All the reads and writes are unbuffered, passed directly to the
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// underlying file. Seeking is done in O(log(N)), where N is the number of
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// extents in the file, but sequential reads jump to the next extent in O(1).
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namespace bsdiff {
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ExtentsFile::ExtentsFile(std::unique_ptr<FileInterface> file,
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const std::vector<ex_t>& extents)
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: file_(std::move(file)), extents_(extents) {
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acc_len_.reserve(extents.size());
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for (const ex_t& extent : extents) {
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acc_len_.push_back(total_ex_len_);
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total_ex_len_ += extent.len;
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}
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}
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ExtentsFile::~ExtentsFile() {
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Close();
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}
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bool ExtentsFile::Read(void* buf, size_t count, size_t* bytes_read) {
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return IOOperation(&FileInterface::Read, buf, count, bytes_read);
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}
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bool ExtentsFile::Write(const void* buf, size_t count, size_t* bytes_written) {
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return IOOperation(&FileInterface::Write, buf, count, bytes_written);
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}
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bool ExtentsFile::Seek(off_t pos) {
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if (pos < 0 || static_cast<uint64_t>(pos) > total_ex_len_)
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return false;
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if (acc_len_.empty())
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return true;
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// Note that the first element of acc_len_ is always 0, and pos is at least 0,
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// so the upper_bound will never return acc_len_.begin().
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curr_pos_ = pos;
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curr_ex_idx_ = std::upper_bound(acc_len_.begin(), acc_len_.end(), pos) -
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acc_len_.begin();
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// We handle the corner case where |pos| is the size of all the extents by
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// leaving the value of curr_ex_idx_ the same way AdvancePos(0) would leave it
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// after the seek.
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if (curr_pos_ < total_ex_len_)
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curr_ex_idx_--;
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return true;
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}
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bool ExtentsFile::Close() {
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return file_->Close();
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}
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bool ExtentsFile::GetSize(uint64_t* size) {
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*size = total_ex_len_;
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return true;
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}
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void ExtentsFile::AdvancePos(uint64_t size) {
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curr_pos_ += size;
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for (; curr_ex_idx_ < extents_.size(); curr_ex_idx_++) {
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if (curr_pos_ < acc_len_[curr_ex_idx_] + extents_[curr_ex_idx_].len)
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return;
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}
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}
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template <typename T>
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bool ExtentsFile::IOOperation(bool (FileInterface::*io_op)(T*, size_t, size_t*),
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T* buf,
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size_t count,
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size_t* bytes_processed) {
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bool result = true;
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size_t processed = 0;
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AdvancePos(0);
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while (count > 0 && curr_ex_idx_ < extents_.size()) {
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const ex_t& ex = extents_[curr_ex_idx_];
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off_t curr_ex_off = curr_pos_ - acc_len_[curr_ex_idx_];
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size_t chunk_size =
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std::min(static_cast<uint64_t>(count), ex.len - curr_ex_off);
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size_t chunk_processed = 0;
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if (ex.off < 0) {
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chunk_processed = chunk_size;
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} else {
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if (!file_->Seek(ex.off + curr_ex_off) ||
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!(file_.get()->*io_op)(buf, chunk_size, &chunk_processed)) {
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processed += chunk_processed;
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result = processed > 0;
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break;
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}
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}
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processed += chunk_processed;
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count -= chunk_processed;
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// T can be either const void* or void*. We const_cast it back to void* and
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// then char* to do the arithmetic operation, but |buf| will continue to be
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// const void* if it was defined that way.
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buf = static_cast<char*>(const_cast<void*>(buf)) + chunk_processed;
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AdvancePos(chunk_processed);
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if (!chunk_processed)
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break;
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}
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*bytes_processed = processed;
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return result;
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}
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} // namespace bsdiff
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