Merge "libdm: Add helper classes for loop control." (516ec4c2) · Commits · e / os / android_system_core

fs_mgr/libdm/Android.bp

+3 −1

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		@@ -28,7 +28,8 @@ cc_library_static {
		srcs: [
		"dm_table.cpp",
		"dm_target.cpp",
		"dm.cpp"
		"dm.cpp",
		"loop_control.cpp",
		],

		header_libs: [
		@@ -47,5 +48,6 @@ cc_test {
		],
		srcs: [
		"dm_test.cpp",
		"loop_control_test.cpp",
		]
		}

fs_mgr/libdm/include/libdm/loop_control.h

0 → 100644

+82 −0

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		/*
		* Copyright 2018 Google, Inc
		*
		* 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.
		*/

		#ifndef _LIBDM_LOOP_CONTROL_H_
		#define _LIBDM_LOOP_CONTROL_H_

		#include <string>

		#include <android-base/unique_fd.h>

		namespace android {
		namespace dm {

		class LoopControl final {
		public:
		LoopControl();

		// Attaches the file specified by 'file_fd' to the loop device specified
		// by 'loopdev'
		bool Attach(int file_fd, std::string* loopdev) const;

		// Detach the loop device given by 'loopdev' from the attached backing file.
		bool Detach(const std::string& loopdev) const;

		LoopControl(const LoopControl&) = delete;
		LoopControl& operator=(const LoopControl&) = delete;
		LoopControl& operator=(LoopControl&&) = default;
		LoopControl(LoopControl&&) = default;

		private:
		bool FindFreeLoopDevice(std::string* loopdev) const;

		static constexpr const char* kLoopControlDevice = "/dev/loop-control";

		android::base::unique_fd control_fd_;
		};

		// Create a temporary loop device around a file descriptor or path.
		class LoopDevice {
		public:
		// Create a loop device for the given file descriptor. It is closed when
		// LoopDevice is destroyed only if auto_close is true.
		LoopDevice(int fd, bool auto_close = false);
		// Create a loop device for the given file path. It will be opened for
		// reading and writing and closed when the loop device is detached.
		explicit LoopDevice(const std::string& path);
		~LoopDevice();

		bool valid() const { return fd_ != -1 && !device_.empty(); }
		const std::string& device() const { return device_; }

		LoopDevice(const LoopDevice&) = delete;
		LoopDevice& operator=(const LoopDevice&) = delete;
		LoopDevice& operator=(LoopDevice&&) = default;
		LoopDevice(LoopDevice&&) = default;

		private:
		void Init();

		android::base::unique_fd fd_;
		bool owns_fd_;
		std::string device_;
		LoopControl control_;
		};

		} // namespace dm
		} // namespace android

		#endif /* _LIBDM_LOOP_CONTROL_H_ */

fs_mgr/libdm/loop_control.cpp

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		/*
		* 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/loop_control.h"

		#include <fcntl.h>
		#include <linux/loop.h>
		#include <stdint.h>
		#include <sys/ioctl.h>
		#include <sys/types.h>
		#include <unistd.h>

		#include <android-base/logging.h>
		#include <android-base/stringprintf.h>
		#include <android-base/unique_fd.h>

		namespace android {
		namespace dm {

		LoopControl::LoopControl() : control_fd_(-1) {
		control_fd_.reset(TEMP_FAILURE_RETRY(open(kLoopControlDevice, O_RDWR \| O_CLOEXEC)));
		if (control_fd_ < 0) {
		PLOG(ERROR) << "Failed to open loop-control";
		}
		}

		bool LoopControl::Attach(int file_fd, std::string* loopdev) const {
		if (!FindFreeLoopDevice(loopdev)) {
		LOG(ERROR) << "Failed to attach, no free loop devices";
		return false;
		}

		android::base::unique_fd loop_fd(TEMP_FAILURE_RETRY(open(loopdev->c_str(), O_RDWR \| O_CLOEXEC)));
		if (loop_fd < 0) {
		PLOG(ERROR) << "Failed to open: " << *loopdev;
		return false;
		}

		int rc = ioctl(loop_fd, LOOP_SET_FD, file_fd);
		if (rc < 0) {
		PLOG(ERROR) << "Failed LOOP_SET_FD";
		return false;
		}
		return true;
		}

		bool LoopControl::Detach(const std::string& loopdev) const {
		if (loopdev.empty()) {
		LOG(ERROR) << "Must provide a loop device";
		return false;
		}

		android::base::unique_fd loop_fd(TEMP_FAILURE_RETRY(open(loopdev.c_str(), O_RDWR \| O_CLOEXEC)));
		if (loop_fd < 0) {
		PLOG(ERROR) << "Failed to open: " << loopdev;
		return false;
		}

		int rc = ioctl(loop_fd, LOOP_CLR_FD, 0);
		if (rc) {
		PLOG(ERROR) << "Failed LOOP_CLR_FD for '" << loopdev << "'";
		return false;
		}
		return true;
		}

		bool LoopControl::FindFreeLoopDevice(std::string* loopdev) const {
		int rc = ioctl(control_fd_, LOOP_CTL_GET_FREE);
		if (rc < 0) {
		PLOG(ERROR) << "Failed to get free loop device";
		return false;
		}

		// Ueventd on android creates all loop devices as /dev/block/loopX
		// The total number of available devices is determined by 'loop.max_part'
		// kernel command line argument.
		*loopdev = ::android::base::StringPrintf("/dev/block/loop%d", rc);
		return true;
		}

		LoopDevice::LoopDevice(int fd, bool auto_close) : fd_(fd), owns_fd_(auto_close) {
		Init();
		}

		LoopDevice::LoopDevice(const std::string& path) : fd_(-1), owns_fd_(true) {
		fd_.reset(open(path.c_str(), O_RDWR \| O_CLOEXEC));
		if (fd_ < -1) {
		PLOG(ERROR) << "open failed for " << path;
		return;
		}
		Init();
		}

		LoopDevice::~LoopDevice() {
		if (valid()) {
		control_.Detach(device_);
		}
		if (!owns_fd_) {
		(void)fd_.release();
		}
		}

		void LoopDevice::Init() {
		control_.Attach(fd_, &device_);
		}

		} // namespace dm
		} // namespace android

fs_mgr/libdm/loop_control_test.cpp

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+65 −0

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		/*
		* 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/loop_control.h"

		#include <fcntl.h>
		#include <linux/memfd.h>
		#include <stdio.h>
		#include <stdlib.h>
		#include <sys/stat.h>
		#include <sys/syscall.h>
		#include <sys/types.h>
		#include <unistd.h>

		#include <android-base/file.h>
		#include <android-base/unique_fd.h>
		#include <gtest/gtest.h>

		using namespace std;
		using namespace android::dm;
		using unique_fd = android::base::unique_fd;

		static unique_fd TempFile() {
		// A loop device needs to be at least one sector to actually work, so fill
		// up the file with a message.
		unique_fd fd(syscall(__NR_memfd_create, "fake_disk", 0));
		if (fd < 0) {
		return {};
		}
		char buffer[] = "Hello";
		for (size_t i = 0; i < 1000; i++) {
		if (!android::base::WriteFully(fd, buffer, sizeof(buffer))) {
		perror("write");
		return {};
		}
		}
		return fd;
		}

		TEST(libdm, LoopControl) {
		unique_fd fd = TempFile();
		ASSERT_GE(fd, 0);

		LoopDevice loop(fd);
		ASSERT_TRUE(loop.valid());

		char buffer[6];
		unique_fd loop_fd(open(loop.device().c_str(), O_RDWR));
		ASSERT_GE(loop_fd, 0);
		ASSERT_TRUE(android::base::ReadFully(loop_fd, buffer, sizeof(buffer)));
		ASSERT_EQ(memcmp(buffer, "Hello", 6), 0);
		}