Check for COW space before writing to COW
This gives a more detailed message when we run out of cow space.
Also, previously, it's possible that the COW op metadata writes
successfully but op data fails due to out of space, resulting in a
broken COW image. After this change, we won't write anything unless
there's sufficient space for both OP metadata and block data. This makes
COW operations more atomic and easier to debug/inspect.
Test: th
Change-Id: I6c1347e91b4ec2d7e434b47a0f47b290e288e600
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
index b93fd32..a9682a1 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
@@ -16,6 +16,7 @@
#include <stdint.h>
+#include <cstdint>
#include <memory>
#include <optional>
#include <string>
@@ -150,6 +151,7 @@
bool SetFd(android::base::borrowed_fd fd);
bool Sync();
bool Truncate(off_t length);
+ bool EnsureSpaceAvailable(const uint64_t bytes_needed) const;
private:
android::base::unique_fd owned_fd_;
@@ -165,6 +167,7 @@
bool is_dev_null_ = false;
bool merge_in_progress_ = false;
bool is_block_device_ = false;
+ uint64_t cow_image_size_ = INT64_MAX;
};
} // namespace snapshot
diff --git a/fs_mgr/libsnapshot/libsnapshot_cow/cow_writer.cpp b/fs_mgr/libsnapshot/libsnapshot_cow/cow_writer.cpp
index 5f5d1fb..43c17a6 100644
--- a/fs_mgr/libsnapshot/libsnapshot_cow/cow_writer.cpp
+++ b/fs_mgr/libsnapshot/libsnapshot_cow/cow_writer.cpp
@@ -30,9 +30,29 @@
#include <lz4.h>
#include <zlib.h>
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
namespace android {
namespace snapshot {
+namespace {
+std::string GetFdPath(int fd) {
+ const auto fd_path = "/proc/self/fd/" + std::to_string(fd);
+ std::string file_path(512, '\0');
+ const auto err = readlink(fd_path.c_str(), file_path.data(), file_path.size());
+ if (err <= 0) {
+ PLOG(ERROR) << "Failed to determine path for fd " << fd;
+ file_path.clear();
+ } else {
+ file_path.resize(err);
+ }
+ return file_path;
+}
+} // namespace
+
static_assert(sizeof(off_t) == sizeof(uint64_t));
using android::base::borrowed_fd;
@@ -163,12 +183,25 @@
} else {
fd_ = fd;
- struct stat stat;
+ struct stat stat {};
if (fstat(fd.get(), &stat) < 0) {
PLOG(ERROR) << "fstat failed";
return false;
}
+ const auto file_path = GetFdPath(fd.get());
is_block_device_ = S_ISBLK(stat.st_mode);
+ if (is_block_device_) {
+ uint64_t size_in_bytes = 0;
+ if (ioctl(fd.get(), BLKGETSIZE64, &size_in_bytes)) {
+ PLOG(ERROR) << "Failed to get total size for: " << fd.get();
+ return false;
+ }
+ cow_image_size_ = size_in_bytes;
+ LOG(INFO) << "COW image " << file_path << " has size " << size_in_bytes;
+ } else {
+ LOG(INFO) << "COW image " << file_path
+ << " is not a block device, assuming unlimited space.";
+ }
}
return true;
}
@@ -343,7 +376,8 @@
op.data_length = static_cast<uint16_t>(data.size());
if (!WriteOperation(op, data.data(), data.size())) {
- PLOG(ERROR) << "AddRawBlocks: write failed";
+ PLOG(ERROR) << "AddRawBlocks: write failed, bytes requested: " << size
+ << ", bytes written: " << i * header_.block_size;
return false;
}
} else {
@@ -512,12 +546,26 @@
return true;
}
-bool CowWriter::WriteOperation(const CowOperation& op, const void* data, size_t size) {
- if (lseek(fd_.get(), next_op_pos_, SEEK_SET) < 0) {
- PLOG(ERROR) << "lseek failed for writing operation.";
+bool CowWriter::EnsureSpaceAvailable(const uint64_t bytes_needed) const {
+ if (bytes_needed > cow_image_size_) {
+ LOG(ERROR) << "No space left on COW device. Required: " << bytes_needed
+ << ", available: " << cow_image_size_;
+ errno = ENOSPC;
return false;
}
- if (!android::base::WriteFully(fd_, reinterpret_cast<const uint8_t*>(&op), sizeof(op))) {
+ return true;
+}
+
+bool CowWriter::WriteOperation(const CowOperation& op, const void* data, size_t size) {
+ if (!EnsureSpaceAvailable(next_op_pos_ + sizeof(op))) {
+ return false;
+ }
+ if (!EnsureSpaceAvailable(next_data_pos_ + size)) {
+ return false;
+ }
+
+ if (!android::base::WriteFullyAtOffset(fd_, reinterpret_cast<const uint8_t*>(&op), sizeof(op),
+ next_op_pos_)) {
return false;
}
if (data != nullptr && size > 0) {
@@ -542,13 +590,8 @@
next_op_pos_ += sizeof(CowOperation) + GetNextOpOffset(op, header_.cluster_ops);
}
-bool CowWriter::WriteRawData(const void* data, size_t size) {
- if (lseek(fd_.get(), next_data_pos_, SEEK_SET) < 0) {
- PLOG(ERROR) << "lseek failed for writing data.";
- return false;
- }
-
- if (!android::base::WriteFully(fd_, data, size)) {
+bool CowWriter::WriteRawData(const void* data, const size_t size) {
+ if (!android::base::WriteFullyAtOffset(fd_, data, size, next_data_pos_)) {
return false;
}
return true;
