libsnapshot: Add an open /dev/null mode for CowWriter.
This will be used by payload_generator to estimate the COW size without
using extra storage space.
Bug: 168554689
Test: cow_api_test, ota_from_target_files
Change-Id: I095c809e7d81eff5321b86f4c6bdfb6e9467e84e
diff --git a/fs_mgr/libsnapshot/cow_writer.cpp b/fs_mgr/libsnapshot/cow_writer.cpp
index 8704eb9..632c866 100644
--- a/fs_mgr/libsnapshot/cow_writer.cpp
+++ b/fs_mgr/libsnapshot/cow_writer.cpp
@@ -110,15 +110,28 @@
return true;
}
+bool CowWriter::SetFd(android::base::borrowed_fd fd) {
+ if (fd.get() < 0) {
+ owned_fd_.reset(open("/dev/null", O_RDWR | O_CLOEXEC));
+ if (owned_fd_ < 0) {
+ PLOG(ERROR) << "open /dev/null failed";
+ return false;
+ }
+ fd_ = owned_fd_;
+ is_dev_null_ = true;
+ } else {
+ fd_ = fd;
+ }
+ return true;
+}
+
bool CowWriter::Initialize(unique_fd&& fd, OpenMode mode) {
owned_fd_ = std::move(fd);
return Initialize(borrowed_fd{owned_fd_}, mode);
}
bool CowWriter::Initialize(borrowed_fd fd, OpenMode mode) {
- fd_ = fd;
-
- if (!ParseOptions()) {
+ if (!SetFd(fd) || !ParseOptions()) {
return false;
}
@@ -139,9 +152,7 @@
}
bool CowWriter::InitializeAppend(android::base::borrowed_fd fd, uint64_t label) {
- fd_ = fd;
-
- if (!ParseOptions()) {
+ if (!SetFd(fd) || !ParseOptions()) {
return false;
}
@@ -304,7 +315,7 @@
CowOperation op = {};
op.type = kCowLabelOp;
op.source = label;
- return WriteOperation(op) && !fsync(fd_.get());
+ return WriteOperation(op) && Sync();
}
std::basic_string<uint8_t> CowWriter::Compress(const void* data, size_t length) {
@@ -383,7 +394,7 @@
PLOG(ERROR) << "lseek ops failed";
return false;
}
- return !fsync(fd_.get());
+ return Sync();
}
uint64_t CowWriter::GetCowSize() {
@@ -424,5 +435,16 @@
return true;
}
+bool CowWriter::Sync() {
+ if (is_dev_null_) {
+ return true;
+ }
+ if (fsync(fd_.get()) < 0) {
+ PLOG(ERROR) << "fsync failed";
+ return false;
+ }
+ return true;
+}
+
} // namespace snapshot
} // namespace android
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
index 50ce5bc..35690d4 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h
@@ -90,6 +90,9 @@
// If opening for write, the file starts from the beginning.
// If opening for append, if the file has a footer, we start appending to the last op.
// If the footer isn't found, the last label is considered corrupt, and dropped.
+ //
+ // If fd is < 0, the CowWriter will be opened against /dev/null. This is for
+ // computing COW sizes without using storage space.
bool Initialize(android::base::unique_fd&& fd, OpenMode mode = OpenMode::WRITE);
bool Initialize(android::base::borrowed_fd fd, OpenMode mode = OpenMode::WRITE);
// Set up a writer, assuming that the given label is the last valid label.
@@ -119,6 +122,9 @@
void AddOperation(const CowOperation& op);
std::basic_string<uint8_t> Compress(const void* data, size_t length);
+ bool SetFd(android::base::borrowed_fd fd);
+ bool Sync();
+
private:
android::base::unique_fd owned_fd_;
android::base::borrowed_fd fd_;
@@ -126,6 +132,7 @@
CowFooter footer_{};
int compression_ = 0;
uint64_t next_op_pos_ = 0;
+ bool is_dev_null_ = false;
// :TODO: this is not efficient, but stringstream ubsan aborts because some
// bytes overflow a signed char.