fs_mgr/libdm/dm.cpp - third_party/android/platform/system/core - Git at Google

 /*
  * Copyright (C) 2018 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 "libdm/dm.h"

 #include <sys/ioctl.h>
 #include <sys/sysmacros.h>
 #include <sys/types.h>

 #include <android-base/logging.h>
 #include <android-base/macros.h>

 namespace android {
 namespace dm {

 DeviceMapper::DeviceMapper() : fd_(-1) {
     fd_ = TEMP_FAILURE_RETRY(open("/dev/device-mapper", O_RDWR | O_CLOEXEC));
     if (fd_ < 0) {
         PLOG(ERROR) << "Failed to open device-mapper";
     }
 }

 DeviceMapper& DeviceMapper::Instance() {
     static DeviceMapper instance;
     return instance;
 }
 // Creates a new device mapper device
 bool DeviceMapper::CreateDevice(const std::string& name) {
     if (name.empty()) {
         LOG(ERROR) << "Unnamed device mapper device creation is not supported";
         return false;
     }

     if (name.size() >= DM_NAME_LEN) {
         LOG(ERROR) << "[" << name << "] is too long to be device mapper name";
         return false;
     }

     struct dm_ioctl io;
     InitIo(&io, name);

     if (ioctl(fd_, DM_DEV_CREATE, &io)) {
         PLOG(ERROR) << "DM_DEV_CREATE failed for [" << name << "]";
         return false;
     }

     // Check to make sure the newly created device doesn't already have targets
     // added or opened by someone
     CHECK(io.target_count == 0) << "Unexpected targets for newly created [" << name << "] device";
     CHECK(io.open_count == 0) << "Unexpected opens for newly created [" << name << "] device";

     // Creates a new device mapper device with the name passed in
     return true;
 }

 bool DeviceMapper::DeleteDevice(const std::string& name) {
     if (name.empty()) {
         LOG(ERROR) << "Unnamed device mapper device creation is not supported";
         return false;
     }

     if (name.size() >= DM_NAME_LEN) {
         LOG(ERROR) << "[" << name << "] is too long to be device mapper name";
         return false;
     }

     struct dm_ioctl io;
     InitIo(&io, name);

     if (ioctl(fd_, DM_DEV_REMOVE, &io)) {
         PLOG(ERROR) << "DM_DEV_REMOVE failed for [" << name << "]";
         return false;
     }

     // Check to make sure appropriate uevent is generated so ueventd will
     // do the right thing and remove the corresponding device node and symlinks.
     CHECK(io.flags & DM_UEVENT_GENERATED_FLAG)
             << "Didn't generate uevent for [" << name << "] removal";

     return true;
 }

 const std::unique_ptr<DmTable> DeviceMapper::table(const std::string& /* name */) const {
     // TODO(b/110035986): Return the table, as read from the kernel instead
     return nullptr;
 }

 DmDeviceState DeviceMapper::GetState(const std::string& name) const {
     struct dm_ioctl io;
     InitIo(&io, name);
     if (ioctl(fd_, DM_DEV_STATUS, &io) < 0) {
         return DmDeviceState::INVALID;
     }
     if ((io.flags & DM_ACTIVE_PRESENT_FLAG) && !(io.flags & DM_SUSPEND_FLAG)) {
         return DmDeviceState::ACTIVE;
     }
     return DmDeviceState::SUSPENDED;
 }

 bool DeviceMapper::CreateDevice(const std::string& name, const DmTable& table) {
     if (!CreateDevice(name)) {
         return false;
     }
     if (!LoadTableAndActivate(name, table)) {
         DeleteDevice(name);
         return false;
     }
     return true;
 }

 bool DeviceMapper::LoadTableAndActivate(const std::string& name, const DmTable& table) {
     std::string ioctl_buffer(sizeof(struct dm_ioctl), 0);
     ioctl_buffer += table.Serialize();

     struct dm_ioctl* io = reinterpret_cast<struct dm_ioctl*>(&ioctl_buffer[0]);
     InitIo(io, name);
     io->data_size = ioctl_buffer.size();
     io->data_start = sizeof(struct dm_ioctl);
     io->target_count = static_cast<uint32_t>(table.num_targets());
     if (table.readonly()) {
         io->flags |= DM_READONLY_FLAG;
     }
     if (ioctl(fd_, DM_TABLE_LOAD, io)) {
         PLOG(ERROR) << "DM_TABLE_LOAD failed";
         return false;
     }

     InitIo(io, name);
     if (ioctl(fd_, DM_DEV_SUSPEND, io)) {
         PLOG(ERROR) << "DM_TABLE_SUSPEND resume failed";
         return false;
     }
     return true;
 }

 // Reads all the available device mapper targets and their corresponding
 // versions from the kernel and returns in a vector
 bool DeviceMapper::GetAvailableTargets(std::vector<DmTargetTypeInfo>* targets) {
     targets->clear();

     // calculate the space needed to read a maximum of kMaxPossibleDmTargets
     uint32_t payload_size = sizeof(struct dm_target_versions);
     payload_size += DM_MAX_TYPE_NAME;
     // device mapper wants every target spec to be aligned at 8-byte boundary
     payload_size = DM_ALIGN(payload_size);
     payload_size *= kMaxPossibleDmTargets;

     uint32_t data_size = sizeof(struct dm_ioctl) + payload_size;
     auto buffer = std::unique_ptr<void, void (*)(void*)>(calloc(1, data_size), free);
     if (buffer == nullptr) {
         LOG(ERROR) << "failed to allocate memory";
         return false;
     }

     // Sets appropriate data size and data_start to make sure we tell kernel
     // about the total size of the buffer we are passing and where to start
     // writing the list of targets.
     struct dm_ioctl* io = reinterpret_cast<struct dm_ioctl*>(buffer.get());
     InitIo(io);
     io->data_size = data_size;
     io->data_start = sizeof(*io);

     if (ioctl(fd_, DM_LIST_VERSIONS, io)) {
         PLOG(ERROR) << "DM_LIST_VERSIONS failed";
         return false;
     }

     // If the provided buffer wasn't enough to list all targets, note that
     // any data beyond sizeof(*io) must not be read in this case
     if (io->flags & DM_BUFFER_FULL_FLAG) {
         LOG(INFO) << data_size << " is not enough memory to list all dm targets";
         return false;
     }

     // if there are no targets registered, return success with empty vector
     if (io->data_size == sizeof(*io)) {
         return true;
     }

     // Parse each target and list the name and version
     // TODO(b/110035986): Templatize this
     uint32_t next = sizeof(*io);
     data_size = io->data_size - next;
     struct dm_target_versions* vers =
             reinterpret_cast<struct dm_target_versions*>(static_cast<char*>(buffer.get()) + next);
     while (next && data_size) {
         targets->emplace_back(vers);
         if (vers->next == 0) {
             break;
         }
         next += vers->next;
         data_size -= vers->next;
         vers = reinterpret_cast<struct dm_target_versions*>(static_cast<char*>(buffer.get()) +
                                                             next);
     }

     return true;
 }

 bool DeviceMapper::GetAvailableDevices(std::vector<DmBlockDevice>* devices) {
     devices->clear();

     // calculate the space needed to read a maximum of 256 targets, each with
     // name with maximum length of 16 bytes
     uint32_t payload_size = sizeof(struct dm_name_list);
     // 128-bytes for the name
     payload_size += DM_NAME_LEN;
     // dm wants every device spec to be aligned at 8-byte boundary
     payload_size = DM_ALIGN(payload_size);
     payload_size *= kMaxPossibleDmDevices;
     uint32_t data_size = sizeof(struct dm_ioctl) + payload_size;
     auto buffer = std::unique_ptr<void, void (*)(void*)>(calloc(1, data_size), free);
     if (buffer == nullptr) {
         LOG(ERROR) << "failed to allocate memory";
         return false;
     }

     // Sets appropriate data size and data_start to make sure we tell kernel
     // about the total size of the buffer we are passing and where to start
     // writing the list of targets.
     struct dm_ioctl* io = reinterpret_cast<struct dm_ioctl*>(buffer.get());
     InitIo(io);
     io->data_size = data_size;
     io->data_start = sizeof(*io);

     if (ioctl(fd_, DM_LIST_DEVICES, io)) {
         PLOG(ERROR) << "DM_LIST_DEVICES failed";
         return false;
     }

     // If the provided buffer wasn't enough to list all devices any data
     // beyond sizeof(*io) must not be read.
     if (io->flags & DM_BUFFER_FULL_FLAG) {
         LOG(INFO) << data_size << " is not enough memory to list all dm devices";
         return false;
     }

     // if there are no devices created yet, return success with empty vector
     if (io->data_size == sizeof(*io)) {
         return true;
     }

     // Parse each device and add a new DmBlockDevice to the vector
     // created from the kernel data.
     uint32_t next = sizeof(*io);
     data_size = io->data_size - next;
     struct dm_name_list* dm_dev =
             reinterpret_cast<struct dm_name_list*>(static_cast<char*>(buffer.get()) + next);

     while (next && data_size) {
         devices->emplace_back((dm_dev));
         if (dm_dev->next == 0) {
             break;
         }
         next += dm_dev->next;
         data_size -= dm_dev->next;
         dm_dev = reinterpret_cast<struct dm_name_list*>(static_cast<char*>(buffer.get()) + next);
     }

     return true;
 }

 // Accepts a device mapper device name (like system_a, vendor_b etc) and
 // returns the path to it's device node (or symlink to the device node)
 bool DeviceMapper::GetDmDevicePathByName(const std::string& name, std::string* path) {
     struct dm_ioctl io;
     InitIo(&io, name);
     if (ioctl(fd_, DM_DEV_STATUS, &io) < 0) {
         PLOG(WARNING) << "DM_DEV_STATUS failed for " << name;
         return false;
     }

     uint32_t dev_num = minor(io.dev);
     *path = "/dev/block/dm-" + std::to_string(dev_num);
     return true;
 }

 bool DeviceMapper::GetTableStatus(const std::string& name, std::vector<TargetInfo>* table) {
     return GetTable(name, 0, table);
 }

 bool DeviceMapper::GetTableInfo(const std::string& name, std::vector<TargetInfo>* table) {
     return GetTable(name, DM_STATUS_TABLE_FLAG, table);
 }

 // private methods of DeviceMapper
 bool DeviceMapper::GetTable(const std::string& name, uint32_t flags,
                             std::vector<TargetInfo>* table) {
     std::vector<char> buffer;
     struct dm_ioctl* io = nullptr;

     for (buffer.resize(4096);; buffer.resize(buffer.size() * 2)) {
         io = reinterpret_cast<struct dm_ioctl*>(&buffer[0]);

         InitIo(io, name);
         io->data_size = buffer.size();
         io->data_start = sizeof(*io);
         io->flags = flags;
         if (ioctl(fd_, DM_TABLE_STATUS, io) < 0) {
             PLOG(ERROR) << "DM_TABLE_STATUS failed for " << name;
             return false;
         }
         if (!(io->flags & DM_BUFFER_FULL_FLAG)) break;
     }

     uint32_t cursor = io->data_start;
     uint32_t data_end = std::min(io->data_size, uint32_t(buffer.size()));
     for (uint32_t i = 0; i < io->target_count; i++) {
         if (cursor + sizeof(struct dm_target_spec) > data_end) {
             break;
         }
         // After each dm_target_spec is a status string. spec->next is an
         // offset from |io->data_start|, and we clamp it to the size of our
         // buffer.
         struct dm_target_spec* spec = reinterpret_cast<struct dm_target_spec*>(&buffer[cursor]);
         uint32_t data_offset = cursor + sizeof(dm_target_spec);
         uint32_t next_cursor = std::min(io->data_start + spec->next, data_end);

         std::string data;
         if (next_cursor > data_offset) {
             // Note: we use c_str() to eliminate any extra trailing 0s.
             data = std::string(&buffer[data_offset], next_cursor - data_offset).c_str();
         }
         table->emplace_back(*spec, data);
         cursor = next_cursor;
     }
     return true;
 }

 void DeviceMapper::InitIo(struct dm_ioctl* io, const std::string& name) const {
     CHECK(io != nullptr) << "nullptr passed to dm_ioctl initialization";
     memset(io, 0, sizeof(*io));

     io->version[0] = DM_VERSION0;
     io->version[1] = DM_VERSION1;
     io->version[2] = DM_VERSION2;
     io->data_size = sizeof(*io);
     io->data_start = 0;
     if (!name.empty()) {
         snprintf(io->name, sizeof(io->name), "%s", name.c_str());
     }
 }

 }  // namespace dm
 }  // namespace android
	/*
	* Copyright (C) 2018 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 "libdm/dm.h"

	#include <sys/ioctl.h>
	#include <sys/sysmacros.h>
	#include <sys/types.h>

	#include <android-base/logging.h>
	#include <android-base/macros.h>

	namespace android {
	namespace dm {

	DeviceMapper::DeviceMapper() : fd_(-1) {
	fd_ = TEMP_FAILURE_RETRY(open("/dev/device-mapper", O_RDWR \| O_CLOEXEC));
	if (fd_ < 0) {
	PLOG(ERROR) << "Failed to open device-mapper";
	}
	}

	DeviceMapper& DeviceMapper::Instance() {
	static DeviceMapper instance;
	return instance;
	}
	// Creates a new device mapper device
	bool DeviceMapper::CreateDevice(const std::string& name) {
	if (name.empty()) {
	LOG(ERROR) << "Unnamed device mapper device creation is not supported";
	return false;
	}

	if (name.size() >= DM_NAME_LEN) {
	LOG(ERROR) << "[" << name << "] is too long to be device mapper name";
	return false;
	}

	struct dm_ioctl io;
	InitIo(&io, name);

	if (ioctl(fd_, DM_DEV_CREATE, &io)) {
	PLOG(ERROR) << "DM_DEV_CREATE failed for [" << name << "]";
	return false;
	}

	// Check to make sure the newly created device doesn't already have targets
	// added or opened by someone
	CHECK(io.target_count == 0) << "Unexpected targets for newly created [" << name << "] device";
	CHECK(io.open_count == 0) << "Unexpected opens for newly created [" << name << "] device";

	// Creates a new device mapper device with the name passed in
	return true;
	}

	bool DeviceMapper::DeleteDevice(const std::string& name) {
	if (name.empty()) {
	LOG(ERROR) << "Unnamed device mapper device creation is not supported";
	return false;
	}

	if (name.size() >= DM_NAME_LEN) {
	LOG(ERROR) << "[" << name << "] is too long to be device mapper name";
	return false;
	}

	struct dm_ioctl io;
	InitIo(&io, name);

	if (ioctl(fd_, DM_DEV_REMOVE, &io)) {
	PLOG(ERROR) << "DM_DEV_REMOVE failed for [" << name << "]";
	return false;
	}

	// Check to make sure appropriate uevent is generated so ueventd will
	// do the right thing and remove the corresponding device node and symlinks.
	CHECK(io.flags & DM_UEVENT_GENERATED_FLAG)
	<< "Didn't generate uevent for [" << name << "] removal";

	return true;
	}

	const std::unique_ptr<DmTable> DeviceMapper::table(const std::string& /* name */) const {
	// TODO(b/110035986): Return the table, as read from the kernel instead
	return nullptr;
	}

	DmDeviceState DeviceMapper::GetState(const std::string& name) const {
	struct dm_ioctl io;
	InitIo(&io, name);
	if (ioctl(fd_, DM_DEV_STATUS, &io) < 0) {
	return DmDeviceState::INVALID;
	}
	if ((io.flags & DM_ACTIVE_PRESENT_FLAG) && !(io.flags & DM_SUSPEND_FLAG)) {
	return DmDeviceState::ACTIVE;
	}
	return DmDeviceState::SUSPENDED;
	}

	bool DeviceMapper::CreateDevice(const std::string& name, const DmTable& table) {
	if (!CreateDevice(name)) {
	return false;
	}
	if (!LoadTableAndActivate(name, table)) {
	DeleteDevice(name);
	return false;
	}
	return true;
	}

	bool DeviceMapper::LoadTableAndActivate(const std::string& name, const DmTable& table) {
	std::string ioctl_buffer(sizeof(struct dm_ioctl), 0);
	ioctl_buffer += table.Serialize();

	struct dm_ioctl* io = reinterpret_cast<struct dm_ioctl*>(&ioctl_buffer[0]);
	InitIo(io, name);
	io->data_size = ioctl_buffer.size();
	io->data_start = sizeof(struct dm_ioctl);
	io->target_count = static_cast<uint32_t>(table.num_targets());
	if (table.readonly()) {
	io->flags \|= DM_READONLY_FLAG;
	}
	if (ioctl(fd_, DM_TABLE_LOAD, io)) {
	PLOG(ERROR) << "DM_TABLE_LOAD failed";
	return false;
	}

	InitIo(io, name);
	if (ioctl(fd_, DM_DEV_SUSPEND, io)) {
	PLOG(ERROR) << "DM_TABLE_SUSPEND resume failed";
	return false;
	}
	return true;
	}

	// Reads all the available device mapper targets and their corresponding
	// versions from the kernel and returns in a vector
	bool DeviceMapper::GetAvailableTargets(std::vector<DmTargetTypeInfo>* targets) {
	targets->clear();

	// calculate the space needed to read a maximum of kMaxPossibleDmTargets
	uint32_t payload_size = sizeof(struct dm_target_versions);
	payload_size += DM_MAX_TYPE_NAME;
	// device mapper wants every target spec to be aligned at 8-byte boundary
	payload_size = DM_ALIGN(payload_size);
	payload_size *= kMaxPossibleDmTargets;

	uint32_t data_size = sizeof(struct dm_ioctl) + payload_size;
	auto buffer = std::unique_ptr<void, void ()(void)>(calloc(1, data_size), free);
	if (buffer == nullptr) {
	LOG(ERROR) << "failed to allocate memory";
	return false;
	}

	// Sets appropriate data size and data_start to make sure we tell kernel
	// about the total size of the buffer we are passing and where to start
	// writing the list of targets.
	struct dm_ioctl* io = reinterpret_cast<struct dm_ioctl*>(buffer.get());
	InitIo(io);
	io->data_size = data_size;
	io->data_start = sizeof(*io);

	if (ioctl(fd_, DM_LIST_VERSIONS, io)) {
	PLOG(ERROR) << "DM_LIST_VERSIONS failed";
	return false;
	}

	// If the provided buffer wasn't enough to list all targets, note that
	// any data beyond sizeof(*io) must not be read in this case
	if (io->flags & DM_BUFFER_FULL_FLAG) {
	LOG(INFO) << data_size << " is not enough memory to list all dm targets";
	return false;
	}

	// if there are no targets registered, return success with empty vector
	if (io->data_size == sizeof(*io)) {
	return true;
	}

	// Parse each target and list the name and version
	// TODO(b/110035986): Templatize this
	uint32_t next = sizeof(*io);
	data_size = io->data_size - next;
	struct dm_target_versions* vers =
	reinterpret_cast<struct dm_target_versions>(static_cast<char>(buffer.get()) + next);
	while (next && data_size) {
	targets->emplace_back(vers);
	if (vers->next == 0) {
	break;
	}
	next += vers->next;
	data_size -= vers->next;
	vers = reinterpret_cast<struct dm_target_versions>(static_cast<char>(buffer.get()) +
	next);
	}

	return true;
	}

	bool DeviceMapper::GetAvailableDevices(std::vector<DmBlockDevice>* devices) {
	devices->clear();

	// calculate the space needed to read a maximum of 256 targets, each with
	// name with maximum length of 16 bytes
	uint32_t payload_size = sizeof(struct dm_name_list);
	// 128-bytes for the name
	payload_size += DM_NAME_LEN;
	// dm wants every device spec to be aligned at 8-byte boundary
	payload_size = DM_ALIGN(payload_size);
	payload_size *= kMaxPossibleDmDevices;
	uint32_t data_size = sizeof(struct dm_ioctl) + payload_size;
	auto buffer = std::unique_ptr<void, void ()(void)>(calloc(1, data_size), free);
	if (buffer == nullptr) {
	LOG(ERROR) << "failed to allocate memory";
	return false;
	}

	// Sets appropriate data size and data_start to make sure we tell kernel
	// about the total size of the buffer we are passing and where to start
	// writing the list of targets.
	struct dm_ioctl* io = reinterpret_cast<struct dm_ioctl*>(buffer.get());
	InitIo(io);
	io->data_size = data_size;
	io->data_start = sizeof(*io);

	if (ioctl(fd_, DM_LIST_DEVICES, io)) {
	PLOG(ERROR) << "DM_LIST_DEVICES failed";
	return false;
	}

	// If the provided buffer wasn't enough to list all devices any data
	// beyond sizeof(*io) must not be read.
	if (io->flags & DM_BUFFER_FULL_FLAG) {
	LOG(INFO) << data_size << " is not enough memory to list all dm devices";
	return false;
	}

	// if there are no devices created yet, return success with empty vector
	if (io->data_size == sizeof(*io)) {
	return true;
	}

	// Parse each device and add a new DmBlockDevice to the vector
	// created from the kernel data.
	uint32_t next = sizeof(*io);
	data_size = io->data_size - next;
	struct dm_name_list* dm_dev =
	reinterpret_cast<struct dm_name_list>(static_cast<char>(buffer.get()) + next);

	while (next && data_size) {
	devices->emplace_back((dm_dev));
	if (dm_dev->next == 0) {
	break;
	}
	next += dm_dev->next;
	data_size -= dm_dev->next;
	dm_dev = reinterpret_cast<struct dm_name_list>(static_cast<char>(buffer.get()) + next);
	}

	return true;
	}

	// Accepts a device mapper device name (like system_a, vendor_b etc) and
	// returns the path to it's device node (or symlink to the device node)
	bool DeviceMapper::GetDmDevicePathByName(const std::string& name, std::string* path) {
	struct dm_ioctl io;
	InitIo(&io, name);
	if (ioctl(fd_, DM_DEV_STATUS, &io) < 0) {
	PLOG(WARNING) << "DM_DEV_STATUS failed for " << name;
	return false;
	}

	uint32_t dev_num = minor(io.dev);
	*path = "/dev/block/dm-" + std::to_string(dev_num);
	return true;
	}

	bool DeviceMapper::GetTableStatus(const std::string& name, std::vector<TargetInfo>* table) {
	return GetTable(name, 0, table);
	}

	bool DeviceMapper::GetTableInfo(const std::string& name, std::vector<TargetInfo>* table) {
	return GetTable(name, DM_STATUS_TABLE_FLAG, table);
	}

	// private methods of DeviceMapper
	bool DeviceMapper::GetTable(const std::string& name, uint32_t flags,
	std::vector<TargetInfo>* table) {
	std::vector<char> buffer;
	struct dm_ioctl* io = nullptr;

	for (buffer.resize(4096);; buffer.resize(buffer.size() * 2)) {
	io = reinterpret_cast<struct dm_ioctl*>(&buffer[0]);

	InitIo(io, name);
	io->data_size = buffer.size();
	io->data_start = sizeof(*io);
	io->flags = flags;
	if (ioctl(fd_, DM_TABLE_STATUS, io) < 0) {
	PLOG(ERROR) << "DM_TABLE_STATUS failed for " << name;
	return false;
	}
	if (!(io->flags & DM_BUFFER_FULL_FLAG)) break;
	}

	uint32_t cursor = io->data_start;
	uint32_t data_end = std::min(io->data_size, uint32_t(buffer.size()));
	for (uint32_t i = 0; i < io->target_count; i++) {
	if (cursor + sizeof(struct dm_target_spec) > data_end) {
	break;
	}
	// After each dm_target_spec is a status string. spec->next is an
	// offset from \|io->data_start\|, and we clamp it to the size of our
	// buffer.
	struct dm_target_spec* spec = reinterpret_cast<struct dm_target_spec*>(&buffer[cursor]);
	uint32_t data_offset = cursor + sizeof(dm_target_spec);
	uint32_t next_cursor = std::min(io->data_start + spec->next, data_end);

	std::string data;
	if (next_cursor > data_offset) {
	// Note: we use c_str() to eliminate any extra trailing 0s.
	data = std::string(&buffer[data_offset], next_cursor - data_offset).c_str();
	}
	table->emplace_back(*spec, data);
	cursor = next_cursor;
	}
	return true;
	}

	void DeviceMapper::InitIo(struct dm_ioctl* io, const std::string& name) const {
	CHECK(io != nullptr) << "nullptr passed to dm_ioctl initialization";
	memset(io, 0, sizeof(*io));

	io->version[0] = DM_VERSION0;
	io->version[1] = DM_VERSION1;
	io->version[2] = DM_VERSION2;
	io->data_size = sizeof(*io);
	io->data_start = 0;
	if (!name.empty()) {
	snprintf(io->name, sizeof(io->name), "%s", name.c_str());
	}
	}

	} // namespace dm
	} // namespace android