secdiscard.cpp: Use getmntent and my newfound C++ knowledge.
Bug: 19706593 Change-Id: I6254e0339ab42fdbecda80c6f37e64c323329190
This commit is contained in:
Paul Crowley
parent
46c7b09e39
commit
4432e73494
2 changed files with 106 additions and 129 deletions
48
AutoCloseFD.h
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48
AutoCloseFD.h
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@ -0,0 +1,48 @@
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/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <string>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <unistd.h>
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// File descriptor which is automatically closed when this object is destroyed.
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// Cannot be copied, since that would cause double-closes.
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class AutoCloseFD {
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public:
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AutoCloseFD(const char *path, int flags = O_RDONLY, int mode = 0):
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fd{TEMP_FAILURE_RETRY(open(path, flags | O_CLOEXEC, mode))} {}
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AutoCloseFD(const std::string &path, int flags = O_RDONLY, int mode = 0):
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AutoCloseFD(path.c_str(), flags, mode) {}
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~AutoCloseFD() {
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if (fd != -1) {
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int preserve_errno = errno;
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if (close(fd) == -1) {
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SLOGE("close(2) failed: %s", strerror(errno));
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};
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errno = preserve_errno;
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}
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}
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AutoCloseFD(const AutoCloseFD&) = delete;
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AutoCloseFD& operator=(const AutoCloseFD&) = delete;
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explicit operator bool() {return fd != -1;}
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int get() const {return fd;}
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private:
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const int fd;
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};
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187
secdiscard.cpp
187
secdiscard.cpp
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@ -24,69 +24,73 @@
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#include <fcntl.h>
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#include <linux/fs.h>
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#include <linux/fiemap.h>
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#include <mntent.h>
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#define LOG_TAG "secdiscard"
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#include "cutils/log.h"
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#include <AutoCloseFD.h>
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namespace {
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// Deliberately limit ourselves to wiping small files.
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#define MAX_WIPE_LENGTH 4096
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#define INIT_BUFFER_SIZE 2048
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constexpr uint64_t max_wipe_length = 4096;
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static void usage(char *progname);
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static void destroy_key(const std::string &path);
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static int file_device_range(const std::string &path, uint64_t range[2]);
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static int open_block_device_for_path(const std::string &path);
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static int read_file_as_string_atomically(const std::string &path, std::string &contents);
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static int find_block_device_for_path(
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const std::string &mounts,
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const std::string &path,
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std::string &block_device);
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void usage(const char *progname);
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int secdiscard_path(const std::string &path);
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int path_device_range(const std::string &path, uint64_t range[2]);
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std::string block_device_for_path(const std::string &path);
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}
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int main(int argc, char **argv) {
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int main(int argc, const char * const argv[]) {
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if (argc != 2 || argv[1][0] != '/') {
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usage(argv[0]);
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return -1;
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}
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SLOGD("Running: %s %s", argv[0], argv[1]);
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std::string target(argv[1]);
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destroy_key(target);
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secdiscard_path(argv[1]);
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if (unlink(argv[1]) != 0 && errno != ENOENT) {
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SLOGE("Unable to delete %s: %s",
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argv[1], strerror(errno));
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return -1;
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}
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SLOGD("Discarded %s", argv[1]);
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return 0;
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}
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static void usage(char *progname) {
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namespace {
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void usage(const char *progname) {
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fprintf(stderr, "Usage: %s <absolute path>\n", progname);
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}
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// BLKSECDISCARD all content in "path", if it's small enough.
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static void destroy_key(const std::string &path) {
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int secdiscard_path(const std::string &path) {
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uint64_t range[2];
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if (file_device_range(path, range) < 0) {
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return;
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if (path_device_range(path, range) == -1) {
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return -1;
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}
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int fs_fd = open_block_device_for_path(path);
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if (fs_fd < 0) {
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return;
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auto block_device = block_device_for_path(path);
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if (block_device.empty()) {
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return -1;
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}
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if (ioctl(fs_fd, BLKSECDISCARD, range) != 0) {
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AutoCloseFD fs_fd(block_device, O_RDWR | O_LARGEFILE);
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if (!fs_fd) {
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SLOGE("Failed to open device %s: %s", block_device.c_str(), strerror(errno));
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return -1;
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}
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if (ioctl(fs_fd.get(), BLKSECDISCARD, range) == -1) {
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SLOGE("Unable to BLKSECDISCARD %s: %s", path.c_str(), strerror(errno));
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close(fs_fd);
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return;
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return -1;
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}
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close(fs_fd);
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SLOGD("Discarded %s", path.c_str());
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return 0;
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}
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// Find a short range that completely covers the file.
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// If there isn't one, return -1, otherwise 0.
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static int file_device_range(const std::string &path, uint64_t range[2])
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int path_device_range(const std::string &path, uint64_t range[2])
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{
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int fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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AutoCloseFD fd(path);
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if (!fd) {
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if (errno == ENOENT) {
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SLOGD("Unable to open %s: %s", path.c_str(), strerror(errno));
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} else {
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@ -102,12 +106,10 @@ static int file_device_range(const std::string &path, uint64_t range[2])
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fiemap->fm_flags = 0;
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fiemap->fm_extent_count = 1;
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fiemap->fm_mapped_extents = 0;
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if (ioctl(fd, FS_IOC_FIEMAP, fiemap) != 0) {
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if (ioctl(fd.get(), FS_IOC_FIEMAP, fiemap) != 0) {
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SLOGE("Unable to FIEMAP %s: %s", path.c_str(), strerror(errno));
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close(fd);
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return -1;
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}
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close(fd);
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if (fiemap->fm_mapped_extents != 1) {
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SLOGE("Expecting one extent, got %d in %s", fiemap->fm_mapped_extents, path.c_str());
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return -1;
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@ -122,7 +124,7 @@ static int file_device_range(const std::string &path, uint64_t range[2])
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SLOGE("Extent has unexpected flags %ulx: %s", extent->fe_flags, path.c_str());
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return -1;
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}
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if (extent->fe_length > MAX_WIPE_LENGTH) {
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if (extent->fe_length > max_wipe_length) {
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SLOGE("Extent too big, %llu bytes in %s", extent->fe_length, path.c_str());
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return -1;
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}
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@ -131,106 +133,33 @@ static int file_device_range(const std::string &path, uint64_t range[2])
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return 0;
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}
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// Given a file path, look for the corresponding
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// block device in /proc/mounts and open it.
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static int open_block_device_for_path(const std::string &path)
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// Given a file path, look for the corresponding block device in /proc/mount
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std::string block_device_for_path(const std::string &path)
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{
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std::string mountsfile("/proc/mounts");
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std::string mounts;
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if (read_file_as_string_atomically(mountsfile, mounts) < 0) {
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return -1;
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std::unique_ptr<FILE, int(*)(FILE*)> mnts(setmntent("/proc/mounts", "re"), endmntent);
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if (!mnts) {
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SLOGE("Unable to open /proc/mounts: %s", strerror(errno));
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return "";
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}
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std::string block_device;
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if (find_block_device_for_path(mounts, path, block_device) < 0) {
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return -1;
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std::string result;
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size_t best_length = 0;
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struct mntent *mnt; // getmntent returns a thread local, so it's safe.
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while ((mnt = getmntent(mnts.get())) != nullptr) {
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auto l = strlen(mnt->mnt_dir);
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if (l > best_length &&
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path.size() > l &&
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path[l] == '/' &&
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path.compare(0, l, mnt->mnt_dir) == 0) {
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result = mnt->mnt_fsname;
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best_length = l;
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}
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}
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SLOGD("For path %s block device is %s", path.c_str(), block_device.c_str());
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int res = open(block_device.c_str(), O_RDWR | O_LARGEFILE | O_CLOEXEC);
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if (res < 0) {
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SLOGE("Failed to open device %s: %s", block_device.c_str(), strerror(errno));
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return -1;
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if (result.empty()) {
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SLOGE("Didn't find a mountpoint to match path %s", path.c_str());
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return "";
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}
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return res;
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SLOGD("For path %s block device is %s", path.c_str(), result.c_str());
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return result;
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}
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// Read a file into a buffer in a single gulp, for atomicity.
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// Null-terminate the buffer.
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// Retry until the buffer is big enough.
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static int read_file_as_string_atomically(const std::string &path, std::string &contents)
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{
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ssize_t buffer_size = INIT_BUFFER_SIZE;
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while (true) {
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int fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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SLOGE("Failed to open %s: %s", path.c_str(), strerror(errno));
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return -1;
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}
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contents.resize(buffer_size);
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ssize_t read_size = read(fd, &contents[0], buffer_size);
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if (read_size < 0) {
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SLOGE("Failed to read from %s: %s", path.c_str(), strerror(errno));
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close(fd);
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return -1;
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}
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close(fd);
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if (read_size < buffer_size) {
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contents.resize(read_size);
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return 0;
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}
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SLOGD("%s too big for buffer of size %zu", path.c_str(), buffer_size);
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buffer_size <<= 1;
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}
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}
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// Search a string representing the contents of /proc/mounts
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// for the mount point of a particular file by prefix matching
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// and return the corresponding block device.
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static int find_block_device_for_path(
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const std::string &mounts,
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const std::string &path,
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std::string &block_device)
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{
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auto line_begin = mounts.begin();
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size_t best_prefix = 0;
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std::string::const_iterator line_end;
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while (line_begin != mounts.end()) {
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line_end = std::find(line_begin, mounts.end(), '\n');
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if (line_end == mounts.end()) {
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break;
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}
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auto device_end = std::find(line_begin, line_end, ' ');
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if (device_end == line_end) {
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break;
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}
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auto mountpoint_begin = device_end + 1;
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auto mountpoint_end = std::find(mountpoint_begin, line_end, ' ');
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if (mountpoint_end == line_end) {
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break;
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}
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if (std::find(line_begin, mountpoint_end, '\\') != mountpoint_end) {
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// We don't correctly handle escape sequences, and we don't expect
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// to encounter any, so fail if we do.
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break;
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}
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size_t mountpoint_len = mountpoint_end - mountpoint_begin;
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if (mountpoint_len > best_prefix &&
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mountpoint_len < path.length() &&
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path[mountpoint_len] == '/' &&
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std::equal(mountpoint_begin, mountpoint_end, path.begin())) {
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block_device = std::string(line_begin, device_end);
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best_prefix = mountpoint_len;
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}
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line_begin = line_end + 1;
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}
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// All of the "break"s above are fatal parse errors.
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if (line_begin != mounts.end()) {
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auto bad_line = std::string(line_begin, line_end);
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SLOGE("Unable to parse line in %s: %s", path.c_str(), bad_line.c_str());
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return -1;
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}
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if (best_prefix == 0) {
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SLOGE("No prefix found for path: %s", path.c_str());
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return -1;
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}
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return 0;
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}
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