Merge "fs_mgr: Change scratch margin to 3 X logical_block_size."

  if higher than 4.6.

- *adb enable-verity* will free up overlayfs and as a bonus the

  device will be reverted pristine to before any content was updated.

- If dynamic partitions runs out of space, resizing a logical

  partition larger may fail because of the scratch partition.

  If this happens, either fastboot flashall or adb enable-verity can

  be used to clear scratch storage to permit the flash.

  Then reinstate the overrides and continue.

- File bugs or submit fixes for review.

        }

        changed = true;

    }

    // Take half of free space, minimum 512MB or free space - 256KB margin.

    // Take half of free space, minimum 512MB or maximum free - margin.

    static constexpr auto kMinimumSize = uint64_t(512 * 1024 * 1024);

    static constexpr auto kMarginSize = uint64_t(256 * 1024);

    if (partition->size() < kMinimumSize) {

        auto partition_size =

                builder->AllocatableSpace() - builder->UsedSpace() + partition->size();

        if ((partition_size > kMinimumSize) || !partition->size()) {

            partition_size = std::max(std::min(kMinimumSize, partition_size - kMarginSize),

            // Leave some space for free space jitter of a few erase

            // blocks, in case they are needed for any individual updates

            // to any other partition that needs to be flashed while

            // overlayfs is in force.  Of course if margin_size is not

            // enough could normally get a flash failure, so

            // ResizePartition() will delete the scratch partition in

            // order to fulfill.  Deleting scratch will destroy all of

            // the adb remount overrides :-( .

            auto margin_size = uint64_t(3 * 256 * 1024);

            BlockDeviceInfo info;

            if (builder->GetBlockDeviceInfo(partition_name, &info)) {

                margin_size = 3 * info.logical_block_size;

            }

            partition_size = std::max(std::min(kMinimumSize, partition_size - margin_size),

                                      partition_size / 2);

            if (partition_size > partition->size()) {

                if (!builder->ResizePartition(partition, partition_size)) {