Alex Deymo | 03f1deb | 2015-10-13 02:15:31 -0700 | [diff] [blame] | 1 | // Copyright 2015 The Chromium OS Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
Alex Deymo | ddf9db5 | 2017-03-02 16:10:41 -0800 | [diff] [blame] | 5 | #include "bsdiff/extents_file.h" |
Alex Deymo | 03f1deb | 2015-10-13 02:15:31 -0700 | [diff] [blame] | 6 | |
| 7 | #include <string.h> |
| 8 | |
| 9 | #include <algorithm> |
| 10 | |
| 11 | // Extent files implementation extending FileInterface. |
| 12 | // |
| 13 | // This class allows to map linear positions in a file to a list of regions in |
| 14 | // another file. All the reads and writes are unbuffered, passed directly to the |
| 15 | // underlying file. Seeking is done in O(log(N)), where N is the number of |
| 16 | // extents in the file, but sequential reads jump to the next extent in O(1). |
| 17 | |
| 18 | namespace bsdiff { |
| 19 | |
| 20 | ExtentsFile::ExtentsFile(std::unique_ptr<FileInterface> file, |
| 21 | const std::vector<ex_t>& extents) |
| 22 | : file_(std::move(file)), extents_(extents) { |
| 23 | acc_len_.reserve(extents.size()); |
| 24 | for (const ex_t& extent : extents) { |
| 25 | acc_len_.push_back(total_ex_len_); |
| 26 | total_ex_len_ += extent.len; |
| 27 | } |
| 28 | } |
| 29 | |
| 30 | ExtentsFile::~ExtentsFile() { |
| 31 | Close(); |
| 32 | } |
| 33 | |
| 34 | bool ExtentsFile::Read(void* buf, size_t count, size_t* bytes_read) { |
| 35 | return IOOperation(&FileInterface::Read, buf, count, bytes_read); |
| 36 | } |
| 37 | |
| 38 | |
| 39 | bool ExtentsFile::Write(const void* buf, size_t count, size_t* bytes_written) { |
| 40 | return IOOperation(&FileInterface::Write, buf, count, bytes_written); |
| 41 | } |
| 42 | |
| 43 | bool ExtentsFile::Seek(off_t pos) { |
| 44 | if (pos < 0 || static_cast<uint64_t>(pos) > total_ex_len_) |
| 45 | return false; |
| 46 | if (acc_len_.empty()) |
| 47 | return true; |
| 48 | // Note that the first element of acc_len_ is always 0, and pos is at least 0, |
| 49 | // so the upper_bound will never return acc_len_.begin(). |
| 50 | curr_pos_ = pos; |
| 51 | curr_ex_idx_ = std::upper_bound(acc_len_.begin(), acc_len_.end(), pos) - |
| 52 | acc_len_.begin(); |
| 53 | // We handle the corner case where |pos| is the size of all the extents by |
| 54 | // leaving the value of curr_ex_idx_ the same way AdvancePos(0) would leave it |
| 55 | // after the seek. |
| 56 | if (curr_pos_ < total_ex_len_) |
| 57 | curr_ex_idx_--; |
| 58 | return true; |
| 59 | } |
| 60 | |
| 61 | bool ExtentsFile::Close() { |
| 62 | return file_->Close(); |
| 63 | } |
| 64 | |
Alex Deymo | daf3516 | 2015-10-14 20:43:15 -0700 | [diff] [blame] | 65 | bool ExtentsFile::GetSize(uint64_t* size) { |
| 66 | *size = total_ex_len_; |
| 67 | return true; |
| 68 | } |
| 69 | |
Alex Deymo | 03f1deb | 2015-10-13 02:15:31 -0700 | [diff] [blame] | 70 | void ExtentsFile::AdvancePos(uint64_t size) { |
| 71 | curr_pos_ += size; |
| 72 | for (; curr_ex_idx_ < extents_.size(); curr_ex_idx_++) { |
| 73 | if (curr_pos_ < acc_len_[curr_ex_idx_] + extents_[curr_ex_idx_].len) |
| 74 | return; |
| 75 | } |
Alex Deymo | 03f1deb | 2015-10-13 02:15:31 -0700 | [diff] [blame] | 76 | } |
| 77 | |
| 78 | template <typename T> |
| 79 | bool ExtentsFile::IOOperation(bool (FileInterface::*io_op)(T*, size_t, size_t*), |
| 80 | T* buf, |
| 81 | size_t count, |
| 82 | size_t* bytes_processed) { |
| 83 | bool result = true; |
| 84 | size_t processed = 0; |
| 85 | AdvancePos(0); |
| 86 | while (count > 0 && curr_ex_idx_ < extents_.size()) { |
| 87 | const ex_t& ex = extents_[curr_ex_idx_]; |
Sen Jiang | f822e6c | 2015-11-24 13:44:00 -0800 | [diff] [blame] | 88 | off_t curr_ex_off = curr_pos_ - acc_len_[curr_ex_idx_]; |
| 89 | size_t chunk_size = |
| 90 | std::min(static_cast<uint64_t>(count), ex.len - curr_ex_off); |
Alex Deymo | 03f1deb | 2015-10-13 02:15:31 -0700 | [diff] [blame] | 91 | size_t chunk_processed = 0; |
| 92 | if (ex.off < 0) { |
| 93 | chunk_processed = chunk_size; |
| 94 | } else { |
Sen Jiang | f822e6c | 2015-11-24 13:44:00 -0800 | [diff] [blame] | 95 | if (!file_->Seek(ex.off + curr_ex_off) || |
| 96 | !(file_.get()->*io_op)(buf, chunk_size, &chunk_processed)) { |
Alex Deymo | 03f1deb | 2015-10-13 02:15:31 -0700 | [diff] [blame] | 97 | processed += chunk_processed; |
| 98 | result = processed > 0; |
| 99 | break; |
| 100 | } |
| 101 | } |
| 102 | processed += chunk_processed; |
| 103 | count -= chunk_processed; |
| 104 | // T can be either const void* or void*. We const_cast it back to void* and |
| 105 | // then char* to do the arithmetic operation, but |buf| will continue to be |
| 106 | // const void* if it was defined that way. |
| 107 | buf = static_cast<char*>(const_cast<void*>(buf)) + chunk_processed; |
| 108 | AdvancePos(chunk_processed); |
| 109 | if (!chunk_processed) |
| 110 | break; |
| 111 | } |
| 112 | *bytes_processed = processed; |
| 113 | return result; |
| 114 | } |
| 115 | |
| 116 | } // namespace bsdiff |