blob: 01d31a6086e789e3b445b2834fcea0d95ac15753 [file] [log] [blame]
// 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.
#include "extents_file.h"
#include <string.h>
#include <algorithm>
// Extent files implementation extending FileInterface.
//
// This class allows to map linear positions in a file to a list of regions in
// another file. All the reads and writes are unbuffered, passed directly to the
// underlying file. Seeking is done in O(log(N)), where N is the number of
// extents in the file, but sequential reads jump to the next extent in O(1).
namespace bsdiff {
ExtentsFile::ExtentsFile(std::unique_ptr<FileInterface> file,
const std::vector<ex_t>& extents)
: file_(std::move(file)), extents_(extents) {
acc_len_.reserve(extents.size());
for (const ex_t& extent : extents) {
acc_len_.push_back(total_ex_len_);
total_ex_len_ += extent.len;
}
}
ExtentsFile::~ExtentsFile() {
Close();
}
bool ExtentsFile::Read(void* buf, size_t count, size_t* bytes_read) {
return IOOperation(&FileInterface::Read, buf, count, bytes_read);
}
bool ExtentsFile::Write(const void* buf, size_t count, size_t* bytes_written) {
return IOOperation(&FileInterface::Write, buf, count, bytes_written);
}
bool ExtentsFile::Seek(off_t pos) {
if (pos < 0 || static_cast<uint64_t>(pos) > total_ex_len_)
return false;
if (acc_len_.empty())
return true;
// Note that the first element of acc_len_ is always 0, and pos is at least 0,
// so the upper_bound will never return acc_len_.begin().
curr_pos_ = pos;
curr_ex_idx_ = std::upper_bound(acc_len_.begin(), acc_len_.end(), pos) -
acc_len_.begin();
// We handle the corner case where |pos| is the size of all the extents by
// leaving the value of curr_ex_idx_ the same way AdvancePos(0) would leave it
// after the seek.
if (curr_pos_ < total_ex_len_)
curr_ex_idx_--;
return true;
}
bool ExtentsFile::Close() {
return file_->Close();
}
bool ExtentsFile::GetSize(uint64_t* size) {
*size = total_ex_len_;
return true;
}
void ExtentsFile::AdvancePos(uint64_t size) {
curr_pos_ += size;
for (; curr_ex_idx_ < extents_.size(); curr_ex_idx_++) {
if (curr_pos_ < acc_len_[curr_ex_idx_] + extents_[curr_ex_idx_].len)
return;
}
return;
}
template <typename T>
bool ExtentsFile::IOOperation(bool (FileInterface::*io_op)(T*, size_t, size_t*),
T* buf,
size_t count,
size_t* bytes_processed) {
bool result = true;
size_t processed = 0;
AdvancePos(0);
while (count > 0 && curr_ex_idx_ < extents_.size()) {
const ex_t& ex = extents_[curr_ex_idx_];
off_t curr_ex_off = curr_pos_ - acc_len_[curr_ex_idx_];
size_t chunk_size =
std::min(static_cast<uint64_t>(count), ex.len - curr_ex_off);
size_t chunk_processed = 0;
if (ex.off < 0) {
chunk_processed = chunk_size;
} else {
if (!file_->Seek(ex.off + curr_ex_off) ||
!(file_.get()->*io_op)(buf, chunk_size, &chunk_processed)) {
processed += chunk_processed;
result = processed > 0;
break;
}
}
processed += chunk_processed;
count -= chunk_processed;
// T can be either const void* or void*. We const_cast it back to void* and
// then char* to do the arithmetic operation, but |buf| will continue to be
// const void* if it was defined that way.
buf = static_cast<char*>(const_cast<void*>(buf)) + chunk_processed;
AdvancePos(chunk_processed);
if (!chunk_processed)
break;
}
*bytes_processed = processed;
return result;
}
} // namespace bsdiff