payload_generator/extent_ranges.cc - android_system_update_engine - Gitiles

 //
 // Copyright (C) 2010 The Android Open Source Project
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //

 #include "update_engine/payload_generator/extent_ranges.h"

 #include <algorithm>
 #include <set>
 #include <utility>
 #include <vector>

 #include <base/logging.h>

 #include "update_engine/common/utils.h"
 #include "update_engine/payload_consumer/payload_constants.h"
 #include "update_engine/payload_generator/extent_utils.h"

 using std::vector;

 namespace chromeos_update_engine {

 bool ExtentRanges::ExtentsOverlapOrTouch(const Extent& a, const Extent& b) {
   if (a.start_block() == b.start_block())
     return true;
   if (a.start_block() == kSparseHole || b.start_block() == kSparseHole)
     return false;
   if (a.start_block() < b.start_block()) {
     return a.start_block() + a.num_blocks() >= b.start_block();
   } else {
     return b.start_block() + b.num_blocks() >= a.start_block();
   }
 }

 bool ExtentRanges::ExtentsOverlap(const Extent& a, const Extent& b) {
   if (a.start_block() == b.start_block())
     return a.num_blocks() != 0;
   if (a.start_block() == kSparseHole || b.start_block() == kSparseHole)
     return false;
   if (a.start_block() < b.start_block()) {
     return a.start_block() + a.num_blocks() > b.start_block();
   } else {
     return b.start_block() + b.num_blocks() > a.start_block();
   }
 }

 void ExtentRanges::AddBlock(uint64_t block) {
   // Remember to respect |merge_touching_extents_| setting
   AddExtent(ExtentForRange(block, 1));
 }

 void ExtentRanges::SubtractBlock(uint64_t block) {
   SubtractExtent(ExtentForRange(block, 1));
 }

 namespace {

 Extent UnionOverlappingExtents(const Extent& first, const Extent& second) {
   CHECK_NE(kSparseHole, first.start_block());
   CHECK_NE(kSparseHole, second.start_block());
   uint64_t start = std::min(first.start_block(), second.start_block());
   uint64_t end = std::max(first.start_block() + first.num_blocks(),
                           second.start_block() + second.num_blocks());
   return ExtentForRange(start, end - start);
 }

 }  // namespace

 void ExtentRanges::AddExtent(Extent extent) {
   if (extent.start_block() == kSparseHole || extent.num_blocks() == 0)
     return;

   ExtentSet::iterator begin_del = extent_set_.end();
   ExtentSet::iterator end_del = extent_set_.end();
   uint64_t del_blocks = 0;
   for (ExtentSet::iterator it = extent_set_.begin(), e = extent_set_.end();
        it != e;
        ++it) {
     const bool should_merge = merge_touching_extents_
                                   ? ExtentsOverlapOrTouch(*it, extent)
                                   : ExtentsOverlap(*it, extent);
     if (should_merge) {
       end_del = it;
       ++end_del;
       del_blocks += it->num_blocks();
       if (begin_del == extent_set_.end())
         begin_del = it;

       extent = UnionOverlappingExtents(extent, *it);
     }
   }
   extent_set_.erase(begin_del, end_del);
   extent_set_.insert(extent);
   blocks_ -= del_blocks;
   blocks_ += extent.num_blocks();
 }

 namespace {
 // Returns base - subtractee (set subtraction).
 ExtentRanges::ExtentSet SubtractOverlappingExtents(const Extent& base,
                                                    const Extent& subtractee) {
   ExtentRanges::ExtentSet ret;
   if (subtractee.start_block() > base.start_block()) {
     ret.insert(ExtentForRange(base.start_block(),
                               subtractee.start_block() - base.start_block()));
   }
   uint64_t base_end = base.start_block() + base.num_blocks();
   uint64_t subtractee_end = subtractee.start_block() + subtractee.num_blocks();
   if (base_end > subtractee_end) {
     ret.insert(ExtentForRange(subtractee_end, base_end - subtractee_end));
   }
   return ret;
 }
 }  // namespace

 void ExtentRanges::SubtractExtent(const Extent& extent) {
   if (extent.start_block() == kSparseHole || extent.num_blocks() == 0)
     return;

   ExtentSet::iterator begin_del = extent_set_.end();
   ExtentSet::iterator end_del = extent_set_.end();
   uint64_t del_blocks = 0;
   ExtentSet new_extents;
   for (ExtentSet::iterator it = extent_set_.begin(), e = extent_set_.end();
        it != e;
        ++it) {
     if (!ExtentsOverlap(*it, extent))
       continue;

     if (begin_del == extent_set_.end())
       begin_del = it;
     end_del = it;
     ++end_del;

     del_blocks += it->num_blocks();

     ExtentSet subtraction = SubtractOverlappingExtents(*it, extent);
     for (ExtentSet::iterator jt = subtraction.begin(), je = subtraction.end();
          jt != je;
          ++jt) {
       new_extents.insert(*jt);
       del_blocks -= jt->num_blocks();
     }
   }
   extent_set_.erase(begin_del, end_del);
   extent_set_.insert(new_extents.begin(), new_extents.end());
   blocks_ -= del_blocks;
 }

 void ExtentRanges::AddRanges(const ExtentRanges& ranges) {
   // Remember to respect |merge_touching_extents_| setting
   for (ExtentSet::const_iterator it = ranges.extent_set_.begin(),
                                  e = ranges.extent_set_.end();
        it != e;
        ++it) {
     AddExtent(*it);
   }
 }

 void ExtentRanges::SubtractRanges(const ExtentRanges& ranges) {
   for (ExtentSet::const_iterator it = ranges.extent_set_.begin(),
                                  e = ranges.extent_set_.end();
        it != e;
        ++it) {
     SubtractExtent(*it);
   }
 }

 void ExtentRanges::AddExtents(const vector<Extent>& extents) {
   // Remember to respect |merge_touching_extents_| setting
   for (vector<Extent>::const_iterator it = extents.begin(), e = extents.end();
        it != e;
        ++it) {
     AddExtent(*it);
   }
 }

 void ExtentRanges::SubtractExtents(const vector<Extent>& extents) {
   for (vector<Extent>::const_iterator it = extents.begin(), e = extents.end();
        it != e;
        ++it) {
     SubtractExtent(*it);
   }
 }

 void ExtentRanges::AddRepeatedExtents(
     const ::google::protobuf::RepeatedPtrField<Extent>& exts) {
   // Remember to respect |merge_touching_extents_| setting
   for (int i = 0, e = exts.size(); i != e; ++i) {
     AddExtent(exts.Get(i));
   }
 }

 void ExtentRanges::SubtractRepeatedExtents(
     const ::google::protobuf::RepeatedPtrField<Extent>& exts) {
   for (int i = 0, e = exts.size(); i != e; ++i) {
     SubtractExtent(exts.Get(i));
   }
 }

 bool ExtentRanges::OverlapsWithExtent(const Extent& extent) const {
   for (const auto& entry : GetCandidateRange(extent)) {
     if (ExtentsOverlap(entry, extent)) {
       return true;
     }
   }
   return false;
 }

 bool ExtentRanges::ContainsBlock(uint64_t block) const {
   auto lower = extent_set_.lower_bound(ExtentForRange(block, 1));
   // The block could be on the extent before the one in |lower|.
   if (lower != extent_set_.begin())
     lower--;
   // Any extent starting at block+1 or later is not interesting, so this is the
   // upper limit.
   auto upper = extent_set_.lower_bound(ExtentForRange(block + 1, 0));
   for (auto iter = lower; iter != upper; ++iter) {
     if (iter->start_block() <= block &&
         block < iter->start_block() + iter->num_blocks()) {
       return true;
     }
   }
   return false;
 }

 void ExtentRanges::Dump() const {
   LOG(INFO) << "ExtentRanges Dump. blocks: " << blocks_;
   for (ExtentSet::const_iterator it = extent_set_.begin(),
                                  e = extent_set_.end();
        it != e;
        ++it) {
     LOG(INFO) << "{" << it->start_block() << ", " << it->num_blocks() << "}";
   }
 }

 Extent ExtentForRange(uint64_t start_block, uint64_t num_blocks) {
   Extent ret;
   ret.set_start_block(start_block);
   ret.set_num_blocks(num_blocks);
   return ret;
 }

 Extent ExtentForBytes(uint64_t block_size,
                       uint64_t start_bytes,
                       uint64_t size_bytes) {
   uint64_t start_block = start_bytes / block_size;
   uint64_t end_block = utils::DivRoundUp(start_bytes + size_bytes, block_size);
   return ExtentForRange(start_block, end_block - start_block);
 }

 vector<Extent> ExtentRanges::GetExtentsForBlockCount(uint64_t count) const {
   vector<Extent> out;
   if (count == 0)
     return out;
   uint64_t out_blocks = 0;
   CHECK(count <= blocks_);
   for (ExtentSet::const_iterator it = extent_set_.begin(),
                                  e = extent_set_.end();
        it != e;
        ++it) {
     const uint64_t blocks_needed = count - out_blocks;
     const Extent& extent = *it;
     out.push_back(extent);
     out_blocks += extent.num_blocks();
     if (extent.num_blocks() < blocks_needed)
       continue;
     if (extent.num_blocks() == blocks_needed)
       break;
     // If we get here, we just added the last extent needed, but it's too big
     out_blocks -= extent.num_blocks();
     out_blocks += blocks_needed;
     out.back().set_num_blocks(blocks_needed);
     break;
   }
   CHECK(out_blocks == utils::BlocksInExtents(out));
   return out;
 }

 Range<ExtentRanges::ExtentSet::const_iterator> ExtentRanges::GetCandidateRange(
     const Extent& extent) const {
   auto lower_it = extent_set_.lower_bound(extent);
   if (lower_it != extent_set_.begin()) {
     --lower_it;
   }

   const auto upper_it = extent_set_.upper_bound(
       ExtentForRange(extent.start_block() + extent.num_blocks(), 1));
   return {lower_it, upper_it};
 }

 std::vector<Extent> ExtentRanges::GetIntersectingExtents(
     const Extent& extent) const {
   const auto candidates = GetCandidateRange(extent);
   std::vector<Extent> result;
   for (const auto& ext : candidates) {
     if (auto intersection = GetOverlapExtent(ext, extent);
         intersection.num_blocks() != 0) {
       result.emplace_back(std::move(intersection));
     }
   }
   return result;
 }

 vector<Extent> FilterExtentRanges(const vector<Extent>& extents,
                                   const ExtentRanges& ranges) {
   vector<Extent> result;
   const ExtentRanges::ExtentSet& extent_set = ranges.extent_set();
   for (Extent extent : extents) {
     // The extents are sorted by the start_block. We want to iterate all the
     // Extents in the ExtentSet possibly overlapping the current |extent|. This
     // is achieved by looking from the extent whose start_block is *lower* than
     // the extent.start_block() up to the greatest extent whose start_block is
     // lower than extent.start_block() + extent.num_blocks().
     auto lower = extent_set.lower_bound(extent);
     // We need to decrement the lower_bound to look at the extent that could
     // overlap the beginning of the current |extent|.
     if (lower != extent_set.begin())
       lower--;
     auto upper = extent_set.lower_bound(
         ExtentForRange(extent.start_block() + extent.num_blocks(), 0));
     for (auto iter = lower; iter != upper; ++iter) {
       if (!ExtentRanges::ExtentsOverlap(extent, *iter))
         continue;
       if (iter->start_block() <= extent.start_block()) {
         // We need to cut blocks from the beginning of the |extent|.
         uint64_t cut_blocks =
             iter->start_block() + iter->num_blocks() - extent.start_block();
         if (cut_blocks >= extent.num_blocks()) {
           extent.set_num_blocks(0);
           break;
         }
         extent = ExtentForRange(extent.start_block() + cut_blocks,
                                 extent.num_blocks() - cut_blocks);
       } else {
         // We need to cut blocks on the middle of the extent, possible up to the
         // end of it.
         result.push_back(ExtentForRange(
             extent.start_block(), iter->start_block() - extent.start_block()));
         uint64_t new_start = iter->start_block() + iter->num_blocks();
         uint64_t old_end = extent.start_block() + extent.num_blocks();
         if (new_start >= old_end) {
           extent.set_num_blocks(0);
           break;
         }
         extent = ExtentForRange(new_start, old_end - new_start);
       }
     }
     if (extent.num_blocks() > 0)
       result.push_back(extent);
   }
   return result;
 }

 Extent GetOverlapExtent(const Extent& extent1, const Extent& extent2) {
   if (!ExtentRanges::ExtentsOverlap(extent1, extent2)) {
     return {};
   }
   const auto start_block =
       std::max(extent1.start_block(), extent2.start_block());
   const auto end_block = std::min(extent1.start_block() + extent1.num_blocks(),
                                   extent2.start_block() + extent2.num_blocks());
   return ExtentForRange(start_block, end_block - start_block);
 }

 }  // namespace chromeos_update_engine
	//
	// Copyright (C) 2010 The Android Open Source Project
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	//

	#include "update_engine/payload_generator/extent_ranges.h"

	#include <algorithm>
	#include <set>
	#include <utility>
	#include <vector>

	#include <base/logging.h>

	#include "update_engine/common/utils.h"
	#include "update_engine/payload_consumer/payload_constants.h"
	#include "update_engine/payload_generator/extent_utils.h"

	using std::vector;

	namespace chromeos_update_engine {

	bool ExtentRanges::ExtentsOverlapOrTouch(const Extent& a, const Extent& b) {
	if (a.start_block() == b.start_block())
	return true;
	if (a.start_block() == kSparseHole \|\| b.start_block() == kSparseHole)
	return false;
	if (a.start_block() < b.start_block()) {
	return a.start_block() + a.num_blocks() >= b.start_block();
	} else {
	return b.start_block() + b.num_blocks() >= a.start_block();
	}
	}

	bool ExtentRanges::ExtentsOverlap(const Extent& a, const Extent& b) {
	if (a.start_block() == b.start_block())
	return a.num_blocks() != 0;
	if (a.start_block() == kSparseHole \|\| b.start_block() == kSparseHole)
	return false;
	if (a.start_block() < b.start_block()) {
	return a.start_block() + a.num_blocks() > b.start_block();
	} else {
	return b.start_block() + b.num_blocks() > a.start_block();
	}
	}

	void ExtentRanges::AddBlock(uint64_t block) {
	// Remember to respect \|merge_touching_extents_\| setting
	AddExtent(ExtentForRange(block, 1));
	}

	void ExtentRanges::SubtractBlock(uint64_t block) {
	SubtractExtent(ExtentForRange(block, 1));
	}

	namespace {

	Extent UnionOverlappingExtents(const Extent& first, const Extent& second) {
	CHECK_NE(kSparseHole, first.start_block());
	CHECK_NE(kSparseHole, second.start_block());
	uint64_t start = std::min(first.start_block(), second.start_block());
	uint64_t end = std::max(first.start_block() + first.num_blocks(),
	second.start_block() + second.num_blocks());
	return ExtentForRange(start, end - start);
	}

	} // namespace

	void ExtentRanges::AddExtent(Extent extent) {
	if (extent.start_block() == kSparseHole \|\| extent.num_blocks() == 0)
	return;

	ExtentSet::iterator begin_del = extent_set_.end();
	ExtentSet::iterator end_del = extent_set_.end();
	uint64_t del_blocks = 0;
	for (ExtentSet::iterator it = extent_set_.begin(), e = extent_set_.end();
	it != e;
	++it) {
	const bool should_merge = merge_touching_extents_
	? ExtentsOverlapOrTouch(*it, extent)
	: ExtentsOverlap(*it, extent);
	if (should_merge) {
	end_del = it;
	++end_del;
	del_blocks += it->num_blocks();
	if (begin_del == extent_set_.end())
	begin_del = it;

	extent = UnionOverlappingExtents(extent, *it);
	}
	}
	extent_set_.erase(begin_del, end_del);
	extent_set_.insert(extent);
	blocks_ -= del_blocks;
	blocks_ += extent.num_blocks();
	}

	namespace {
	// Returns base - subtractee (set subtraction).
	ExtentRanges::ExtentSet SubtractOverlappingExtents(const Extent& base,
	const Extent& subtractee) {
	ExtentRanges::ExtentSet ret;
	if (subtractee.start_block() > base.start_block()) {
	ret.insert(ExtentForRange(base.start_block(),
	subtractee.start_block() - base.start_block()));
	}
	uint64_t base_end = base.start_block() + base.num_blocks();
	uint64_t subtractee_end = subtractee.start_block() + subtractee.num_blocks();
	if (base_end > subtractee_end) {
	ret.insert(ExtentForRange(subtractee_end, base_end - subtractee_end));
	}
	return ret;
	}
	} // namespace

	void ExtentRanges::SubtractExtent(const Extent& extent) {
	if (extent.start_block() == kSparseHole \|\| extent.num_blocks() == 0)
	return;

	ExtentSet::iterator begin_del = extent_set_.end();
	ExtentSet::iterator end_del = extent_set_.end();
	uint64_t del_blocks = 0;
	ExtentSet new_extents;
	for (ExtentSet::iterator it = extent_set_.begin(), e = extent_set_.end();
	it != e;
	++it) {
	if (!ExtentsOverlap(*it, extent))
	continue;

	if (begin_del == extent_set_.end())
	begin_del = it;
	end_del = it;
	++end_del;

	del_blocks += it->num_blocks();

	ExtentSet subtraction = SubtractOverlappingExtents(*it, extent);
	for (ExtentSet::iterator jt = subtraction.begin(), je = subtraction.end();
	jt != je;
	++jt) {
	new_extents.insert(*jt);
	del_blocks -= jt->num_blocks();
	}
	}
	extent_set_.erase(begin_del, end_del);
	extent_set_.insert(new_extents.begin(), new_extents.end());
	blocks_ -= del_blocks;
	}

	void ExtentRanges::AddRanges(const ExtentRanges& ranges) {
	// Remember to respect \|merge_touching_extents_\| setting
	for (ExtentSet::const_iterator it = ranges.extent_set_.begin(),
	e = ranges.extent_set_.end();
	it != e;
	++it) {
	AddExtent(*it);
	}
	}

	void ExtentRanges::SubtractRanges(const ExtentRanges& ranges) {
	for (ExtentSet::const_iterator it = ranges.extent_set_.begin(),
	e = ranges.extent_set_.end();
	it != e;
	++it) {
	SubtractExtent(*it);
	}
	}

	void ExtentRanges::AddExtents(const vector<Extent>& extents) {
	// Remember to respect \|merge_touching_extents_\| setting
	for (vector<Extent>::const_iterator it = extents.begin(), e = extents.end();
	it != e;
	++it) {
	AddExtent(*it);
	}
	}

	void ExtentRanges::SubtractExtents(const vector<Extent>& extents) {
	for (vector<Extent>::const_iterator it = extents.begin(), e = extents.end();
	it != e;
	++it) {
	SubtractExtent(*it);
	}
	}

	void ExtentRanges::AddRepeatedExtents(
	const ::google::protobuf::RepeatedPtrField<Extent>& exts) {
	// Remember to respect \|merge_touching_extents_\| setting
	for (int i = 0, e = exts.size(); i != e; ++i) {
	AddExtent(exts.Get(i));
	}
	}

	void ExtentRanges::SubtractRepeatedExtents(
	const ::google::protobuf::RepeatedPtrField<Extent>& exts) {
	for (int i = 0, e = exts.size(); i != e; ++i) {
	SubtractExtent(exts.Get(i));
	}
	}

	bool ExtentRanges::OverlapsWithExtent(const Extent& extent) const {
	for (const auto& entry : GetCandidateRange(extent)) {
	if (ExtentsOverlap(entry, extent)) {
	return true;
	}
	}
	return false;
	}

	bool ExtentRanges::ContainsBlock(uint64_t block) const {
	auto lower = extent_set_.lower_bound(ExtentForRange(block, 1));
	// The block could be on the extent before the one in \|lower\|.
	if (lower != extent_set_.begin())
	lower--;
	// Any extent starting at block+1 or later is not interesting, so this is the
	// upper limit.
	auto upper = extent_set_.lower_bound(ExtentForRange(block + 1, 0));
	for (auto iter = lower; iter != upper; ++iter) {
	if (iter->start_block() <= block &&
	block < iter->start_block() + iter->num_blocks()) {
	return true;
	}
	}
	return false;
	}

	void ExtentRanges::Dump() const {
	LOG(INFO) << "ExtentRanges Dump. blocks: " << blocks_;
	for (ExtentSet::const_iterator it = extent_set_.begin(),
	e = extent_set_.end();
	it != e;
	++it) {
	LOG(INFO) << "{" << it->start_block() << ", " << it->num_blocks() << "}";
	}
	}

	Extent ExtentForRange(uint64_t start_block, uint64_t num_blocks) {
	Extent ret;
	ret.set_start_block(start_block);
	ret.set_num_blocks(num_blocks);
	return ret;
	}

	Extent ExtentForBytes(uint64_t block_size,
	uint64_t start_bytes,
	uint64_t size_bytes) {
	uint64_t start_block = start_bytes / block_size;
	uint64_t end_block = utils::DivRoundUp(start_bytes + size_bytes, block_size);
	return ExtentForRange(start_block, end_block - start_block);
	}

	vector<Extent> ExtentRanges::GetExtentsForBlockCount(uint64_t count) const {
	vector<Extent> out;
	if (count == 0)
	return out;
	uint64_t out_blocks = 0;
	CHECK(count <= blocks_);
	for (ExtentSet::const_iterator it = extent_set_.begin(),
	e = extent_set_.end();
	it != e;
	++it) {
	const uint64_t blocks_needed = count - out_blocks;
	const Extent& extent = *it;
	out.push_back(extent);
	out_blocks += extent.num_blocks();
	if (extent.num_blocks() < blocks_needed)
	continue;
	if (extent.num_blocks() == blocks_needed)
	break;
	// If we get here, we just added the last extent needed, but it's too big
	out_blocks -= extent.num_blocks();
	out_blocks += blocks_needed;
	out.back().set_num_blocks(blocks_needed);
	break;
	}
	CHECK(out_blocks == utils::BlocksInExtents(out));
	return out;
	}

	Range<ExtentRanges::ExtentSet::const_iterator> ExtentRanges::GetCandidateRange(
	const Extent& extent) const {
	auto lower_it = extent_set_.lower_bound(extent);
	if (lower_it != extent_set_.begin()) {
	--lower_it;
	}

	const auto upper_it = extent_set_.upper_bound(
	ExtentForRange(extent.start_block() + extent.num_blocks(), 1));
	return {lower_it, upper_it};
	}

	std::vector<Extent> ExtentRanges::GetIntersectingExtents(
	const Extent& extent) const {
	const auto candidates = GetCandidateRange(extent);
	std::vector<Extent> result;
	for (const auto& ext : candidates) {
	if (auto intersection = GetOverlapExtent(ext, extent);
	intersection.num_blocks() != 0) {
	result.emplace_back(std::move(intersection));
	}
	}
	return result;
	}

	vector<Extent> FilterExtentRanges(const vector<Extent>& extents,
	const ExtentRanges& ranges) {
	vector<Extent> result;
	const ExtentRanges::ExtentSet& extent_set = ranges.extent_set();
	for (Extent extent : extents) {
	// The extents are sorted by the start_block. We want to iterate all the
	// Extents in the ExtentSet possibly overlapping the current \|extent\|. This
	// is achieved by looking from the extent whose start_block is lower than
	// the extent.start_block() up to the greatest extent whose start_block is
	// lower than extent.start_block() + extent.num_blocks().
	auto lower = extent_set.lower_bound(extent);
	// We need to decrement the lower_bound to look at the extent that could
	// overlap the beginning of the current \|extent\|.
	if (lower != extent_set.begin())
	lower--;
	auto upper = extent_set.lower_bound(
	ExtentForRange(extent.start_block() + extent.num_blocks(), 0));
	for (auto iter = lower; iter != upper; ++iter) {
	if (!ExtentRanges::ExtentsOverlap(extent, *iter))
	continue;
	if (iter->start_block() <= extent.start_block()) {
	// We need to cut blocks from the beginning of the \|extent\|.
	uint64_t cut_blocks =
	iter->start_block() + iter->num_blocks() - extent.start_block();
	if (cut_blocks >= extent.num_blocks()) {
	extent.set_num_blocks(0);
	break;
	}
	extent = ExtentForRange(extent.start_block() + cut_blocks,
	extent.num_blocks() - cut_blocks);
	} else {
	// We need to cut blocks on the middle of the extent, possible up to the
	// end of it.
	result.push_back(ExtentForRange(
	extent.start_block(), iter->start_block() - extent.start_block()));
	uint64_t new_start = iter->start_block() + iter->num_blocks();
	uint64_t old_end = extent.start_block() + extent.num_blocks();
	if (new_start >= old_end) {
	extent.set_num_blocks(0);
	break;
	}
	extent = ExtentForRange(new_start, old_end - new_start);
	}
	}
	if (extent.num_blocks() > 0)
	result.push_back(extent);
	}
	return result;
	}

	Extent GetOverlapExtent(const Extent& extent1, const Extent& extent2) {
	if (!ExtentRanges::ExtentsOverlap(extent1, extent2)) {
	return {};
	}
	const auto start_block =
	std::max(extent1.start_block(), extent2.start_block());
	const auto end_block = std::min(extent1.start_block() + extent1.num_blocks(),
	extent2.start_block() + extent2.num_blocks());
	return ExtentForRange(start_block, end_block - start_block);
	}

	} // namespace chromeos_update_engine