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/*
** Copyright 2017, 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 "FileBlobCache.h"
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include <log/log.h>
// Cache file header
static const char* cacheFileMagic = "EGL$";
static const size_t cacheFileHeaderSize = 8;
namespace android {
static uint32_t crc32c(const uint8_t* buf, size_t len) {
const uint32_t polyBits = 0x82F63B78;
uint32_t r = 0;
for (size_t i = 0; i < len; i++) {
r ^= buf[i];
for (int j = 0; j < 8; j++) {
if (r & 1) {
r = (r >> 1) ^ polyBits;
} else {
r >>= 1;
}
}
}
return r;
}
FileBlobCache::FileBlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize,
const std::string& filename)
: BlobCache(maxKeySize, maxValueSize, maxTotalSize)
, mFilename(filename) {
if (mFilename.length() > 0) {
size_t headerSize = cacheFileHeaderSize;
int fd = open(mFilename.c_str(), O_RDONLY, 0);
if (fd == -1) {
if (errno != ENOENT) {
ALOGE("error opening cache file %s: %s (%d)", mFilename.c_str(),
strerror(errno), errno);
}
return;
}
struct stat statBuf;
if (fstat(fd, &statBuf) == -1) {
ALOGE("error stat'ing cache file: %s (%d)", strerror(errno), errno);
close(fd);
return;
}
// Check the size before trying to mmap it.
size_t fileSize = statBuf.st_size;
if (fileSize > mMaxTotalSize * 2) {
ALOGE("cache file is too large: %#" PRIx64,
static_cast<off64_t>(statBuf.st_size));
close(fd);
return;
}
uint8_t* buf = reinterpret_cast<uint8_t*>(mmap(nullptr, fileSize,
PROT_READ, MAP_PRIVATE, fd, 0));
if (buf == MAP_FAILED) {
ALOGE("error mmaping cache file: %s (%d)", strerror(errno),
errno);
close(fd);
return;
}
// Check the file magic and CRC
size_t cacheSize = fileSize - headerSize;
if (memcmp(buf, cacheFileMagic, 4) != 0) {
ALOGE("cache file has bad mojo");
close(fd);
return;
}
uint32_t* crc = reinterpret_cast<uint32_t*>(buf + 4);
if (crc32c(buf + headerSize, cacheSize) != *crc) {
ALOGE("cache file failed CRC check");
close(fd);
return;
}
int err = unflatten(buf + headerSize, cacheSize);
if (err < 0) {
ALOGE("error reading cache contents: %s (%d)", strerror(-err),
-err);
munmap(buf, fileSize);
close(fd);
return;
}
munmap(buf, fileSize);
close(fd);
}
}
void FileBlobCache::writeToFile() {
if (mFilename.length() > 0) {
size_t cacheSize = getFlattenedSize();
size_t headerSize = cacheFileHeaderSize;
const char* fname = mFilename.c_str();
// Try to create the file with no permissions so we can write it
// without anyone trying to read it.
int fd = open(fname, O_CREAT | O_EXCL | O_RDWR, 0);
if (fd == -1) {
if (errno == EEXIST) {
// The file exists, delete it and try again.
if (unlink(fname) == -1) {
// No point in retrying if the unlink failed.
ALOGE("error unlinking cache file %s: %s (%d)", fname,
strerror(errno), errno);
return;
}
// Retry now that we've unlinked the file.
fd = open(fname, O_CREAT | O_EXCL | O_RDWR, 0);
}
if (fd == -1) {
ALOGE("error creating cache file %s: %s (%d)", fname,
strerror(errno), errno);
return;
}
}
size_t fileSize = headerSize + cacheSize;
uint8_t* buf = new uint8_t [fileSize];
if (!buf) {
ALOGE("error allocating buffer for cache contents: %s (%d)",
strerror(errno), errno);
close(fd);
unlink(fname);
return;
}
int err = flatten(buf + headerSize, cacheSize);
if (err < 0) {
ALOGE("error writing cache contents: %s (%d)", strerror(-err),
-err);
delete [] buf;
close(fd);
unlink(fname);
return;
}
// Write the file magic and CRC
memcpy(buf, cacheFileMagic, 4);
uint32_t* crc = reinterpret_cast<uint32_t*>(buf + 4);
*crc = crc32c(buf + headerSize, cacheSize);
if (write(fd, buf, fileSize) == -1) {
ALOGE("error writing cache file: %s (%d)", strerror(errno),
errno);
delete [] buf;
close(fd);
unlink(fname);
return;
}
delete [] buf;
fchmod(fd, S_IRUSR);
close(fd);
}
}
}
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