zircon/system/ulib/storage/operation/unbuffered_operations_builder.cc

// Copyright 2019 The Fuchsia 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 "storage/operation/unbuffered_operations_builder.h"

#include <algorithm>
#include <cstdint>

#include <range/range.h>

namespace storage {

namespace {
using range::Range;

// Skew between the vmo offset and the device offset implies that
// operations should not be combined.
bool EqualVmoDeviceOffsetSkew(const Operation& a, const Operation& b) {
  return (a.vmo_offset - b.vmo_offset) == (a.dev_offset - b.dev_offset);
}

}  // namespace

UnbufferedOperationsBuilder::~UnbufferedOperationsBuilder() {}

void UnbufferedOperationsBuilder::Add(const UnbufferedOperation& new_operation) {
  // Don't merge operations that don't use a VMO.
  if (new_operation.data != nullptr) {
    operations_.push_back(new_operation);
    block_count_ += new_operation.op.length;
    return;
  }

  ZX_DEBUG_ASSERT(new_operation.vmo->is_valid());

  zx::unowned_vmo vmo = zx::unowned_vmo(new_operation.vmo->get());
  uint64_t vmo_offset = new_operation.op.vmo_offset;
  uint64_t dev_offset = new_operation.op.dev_offset;
  uint64_t length = new_operation.op.length;

  if (length == 0) {
    return;
  }

  for (auto& operation : operations_) {
    if ((operation.vmo->get() != vmo->get()) || (operation.op.type != new_operation.op.type) ||
        !EqualVmoDeviceOffsetSkew(operation.op, new_operation.op)) {
      continue;
    }

    // TODO(https://fxbug.dev/42109279): Merge/coalesce is more involved than this. One enqueue can encompass
    // from
    //                one to all existing requests - leading to popping out operations.
    auto old_range =
        Range<uint64_t>(operation.op.vmo_offset, operation.op.vmo_offset + operation.op.length);

    auto new_range = Range<uint64_t>(vmo_offset, vmo_offset + length);
    if (Mergable(old_range, new_range)) {
      new_range.Merge(old_range);
      operation.op.vmo_offset = new_range.Start();
      operation.op.length = new_range.Length();
      operation.op.dev_offset = std::min(dev_offset, operation.op.dev_offset);
      block_count_ += (new_range.Length() - old_range.Length());
      return;
    }
  }

  UnbufferedOperation operation;
  operation.vmo = zx::unowned_vmo(vmo->get());
  operation.op.type = new_operation.op.type;
  operation.op.vmo_offset = vmo_offset;
  operation.op.dev_offset = dev_offset;
  operation.op.length = length;
  operations_.push_back(operation);
  block_count_ += operation.op.length;
}

std::vector<UnbufferedOperation> UnbufferedOperationsBuilder::TakeOperations() {
  block_count_ = 0;
  return std::move(operations_);
}

}  // namespace storage