Add CreateEmptyDevice and WaitForDevice APIs
These APIs support a flow in which dm devices can be created before they
are actually needed, hence minimizing the time a process will wait for
ueventd to create user space paths.
Bug: 190618831
Test: atest libdm_test
Change-Id: I4dfa14e5271a6a13de6da73ec3c7efb1ebc0f8b8
diff --git a/fs_mgr/libdm/dm.cpp b/fs_mgr/libdm/dm.cpp
index c4874b8..a5eda29 100644
--- a/fs_mgr/libdm/dm.cpp
+++ b/fs_mgr/libdm/dm.cpp
@@ -170,19 +170,18 @@
return access("/system/bin/recovery", F_OK) == 0;
}
-bool DeviceMapper::CreateDevice(const std::string& name, const DmTable& table, std::string* path,
- const std::chrono::milliseconds& timeout_ms) {
+bool DeviceMapper::CreateEmptyDevice(const std::string& name) {
std::string uuid = GenerateUuid();
- if (!CreateDevice(name, uuid)) {
- return false;
- }
+ return CreateDevice(name, uuid);
+}
+bool DeviceMapper::WaitForDevice(const std::string& name,
+ const std::chrono::milliseconds& timeout_ms, std::string* path) {
// We use the unique path for testing whether the device is ready. After
// that, it's safe to use the dm-N path which is compatible with callers
// that expect it to be formatted as such.
std::string unique_path;
- if (!LoadTableAndActivate(name, table) || !GetDeviceUniquePath(name, &unique_path) ||
- !GetDmDevicePathByName(name, path)) {
+ if (!GetDeviceUniquePath(name, &unique_path) || !GetDmDevicePathByName(name, path)) {
DeleteDevice(name);
return false;
}
@@ -208,6 +207,25 @@
return true;
}
+bool DeviceMapper::CreateDevice(const std::string& name, const DmTable& table, std::string* path,
+ const std::chrono::milliseconds& timeout_ms) {
+ if (!CreateEmptyDevice(name)) {
+ return false;
+ }
+
+ if (!LoadTableAndActivate(name, table)) {
+ DeleteDevice(name);
+ return false;
+ }
+
+ if (!WaitForDevice(name, timeout_ms, path)) {
+ DeleteDevice(name);
+ return false;
+ }
+
+ return true;
+}
+
bool DeviceMapper::GetDeviceUniquePath(const std::string& name, std::string* path) {
struct dm_ioctl io;
InitIo(&io, name);
diff --git a/fs_mgr/libdm/dm_test.cpp b/fs_mgr/libdm/dm_test.cpp
index 8006db2..8314ec5 100644
--- a/fs_mgr/libdm/dm_test.cpp
+++ b/fs_mgr/libdm/dm_test.cpp
@@ -29,6 +29,7 @@
#include <thread>
#include <android-base/file.h>
+#include <android-base/scopeguard.h>
#include <android-base/strings.h>
#include <android-base/unique_fd.h>
#include <gtest/gtest.h>
@@ -679,3 +680,17 @@
ASSERT_NE(0, access(path.c_str(), F_OK));
ASSERT_EQ(ENOENT, errno);
}
+
+TEST(libdm, CreateEmptyDevice) {
+ DeviceMapper& dm = DeviceMapper::Instance();
+ ASSERT_TRUE(dm.CreateEmptyDevice("empty-device"));
+ auto guard = android::base::make_scope_guard([&]() { dm.DeleteDevice("empty-device", 5s); });
+
+ // Empty device should be in suspended state.
+ ASSERT_EQ(DmDeviceState::SUSPENDED, dm.GetState("empty-device"));
+
+ std::string path;
+ ASSERT_TRUE(dm.WaitForDevice("empty-device", 5s, &path));
+ // Path should exist.
+ ASSERT_EQ(0, access(path.c_str(), F_OK));
+}
diff --git a/fs_mgr/libdm/include/libdm/dm.h b/fs_mgr/libdm/include/libdm/dm.h
index 70b14fa..8fcdf74 100644
--- a/fs_mgr/libdm/include/libdm/dm.h
+++ b/fs_mgr/libdm/include/libdm/dm.h
@@ -115,6 +115,19 @@
// - ACTIVE: resumes the device.
bool ChangeState(const std::string& name, DmDeviceState state);
+ // Creates empty device.
+ // This supports a use case when a caller doesn't need a device straight away, but instead
+ // asks kernel to create it beforehand, thus avoiding blocking itself from waiting for ueventd
+ // to create user space paths.
+ // Callers are expected to then activate their device by calling LoadTableAndActivate function.
+ // To avoid race conditions, callers must still synchronize with ueventd by calling
+ // WaitForDevice function.
+ bool CreateEmptyDevice(const std::string& name);
+
+ // Waits for device paths to be created in the user space.
+ bool WaitForDevice(const std::string& name, const std::chrono::milliseconds& timeout_ms,
+ std::string* path);
+
// Creates a device, loads the given table, and activates it. If the device
// is not able to be activated, it is destroyed, and false is returned.
// After creation, |path| contains the result of calling