Add libdm and dmctl support for dm-user targets

dm-user is very much a WIP and while this may change (we need to figure out how
to get credentials to the dm-user daemon, for example) it seems like a somewhat
safe bet to assume that the behavior will at least include a start/end range.

Test: I just ran "dmctl create palmer user 0 1024", which created the device.
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Change-Id: Ic5f84de6a4f09bf906246035d450edd637cc38ed

fs_mgr/libdm/dm_target.cpp

@@ -280,5 +280,12 @@ std::string DmTargetDefaultKey::GetParameterString() const {
     return android::base::Join(argv, " ");
 }
 
+std::string DmTargetUser::GetParameterString() const {
+    std::vector<std::string> argv;
+    argv.push_back(std::to_string(start()));
+    argv.push_back(std::to_string(size()));
+    return android::base::Join(argv, " ");
+}
+
 }  // namespace dm
 }  // namespace android

fs_mgr/libdm/include/libdm/dm_target.h

@@ -309,6 +309,14 @@ class DmTargetDefaultKey final : public DmTarget {
     bool is_hw_wrapped_ = false;
 };
 
+class DmTargetUser final : public DmTarget {
+  public:
+    DmTargetUser(uint64_t start, uint64_t length) : DmTarget(start, length) {}
+
+    std::string name() const override { return "user"; }
+    std::string GetParameterString() const override;
+};
+
 }  // namespace dm
 }  // namespace android
 

fs_mgr/tools/dmctl.cpp

@@ -174,6 +174,8 @@ class TargetParser final {
             }
             return std::make_unique<DmTargetSnapshot>(start_sector, num_sectors, base_device,
                                                       cow_device, mode, chunk_size);
+        } else if (target_type == "user") {
+            return std::make_unique<DmTargetUser>(start_sector, num_sectors);
         } else {
             std::cerr << "Unrecognized target type: " << target_type << std::endl;
             return nullptr;