diff --git a/fs_mgr/libdm/Android.bp b/fs_mgr/libdm/Android.bp
index c8c2d8355..21255df5f 100644
--- a/fs_mgr/libdm/Android.bp
+++ b/fs_mgr/libdm/Android.bp
@@ -46,6 +46,7 @@ cc_test {
     static_libs: [
         "libdm",
         "libbase",
+        "libfs_mgr",
         "liblog",
     ],
     srcs: [
diff --git a/fs_mgr/libdm/dm.cpp b/fs_mgr/libdm/dm.cpp
index c2917a4b0..788039d60 100644
--- a/fs_mgr/libdm/dm.cpp
+++ b/fs_mgr/libdm/dm.cpp
@@ -302,6 +302,26 @@ bool DeviceMapper::GetDmDevicePathByName(const std::string& name, std::string* p
     return true;
 }
 
+bool DeviceMapper::GetDeviceNumber(const std::string& name, dev_t* dev) {
+    struct dm_ioctl io;
+    InitIo(&io, name);
+    if (ioctl(fd_, DM_DEV_STATUS, &io) < 0) {
+        PLOG(WARNING) << "DM_DEV_STATUS failed for " << name;
+        return false;
+    }
+    *dev = io.dev;
+    return true;
+}
+
+bool DeviceMapper::GetDeviceString(const std::string& name, std::string* dev) {
+    dev_t num;
+    if (!GetDeviceNumber(name, &num)) {
+        return false;
+    }
+    *dev = std::to_string(major(num)) + ":" + std::to_string(minor(num));
+    return true;
+}
+
 bool DeviceMapper::GetTableStatus(const std::string& name, std::vector<TargetInfo>* table) {
     return GetTable(name, 0, table);
 }
diff --git a/fs_mgr/libdm/dm_test.cpp b/fs_mgr/libdm/dm_test.cpp
index dc47c33b0..62199233b 100644
--- a/fs_mgr/libdm/dm_test.cpp
+++ b/fs_mgr/libdm/dm_test.cpp
@@ -132,8 +132,8 @@ TEST(libdm, DmLinear) {
     // Define a 2-sector device, with each sector mapping to the first sector
     // of one of our loop devices.
     DmTable table;
-    ASSERT_TRUE(table.AddTarget(make_unique<DmTargetLinear>(0, 1, loop_a.device(), 0)));
-    ASSERT_TRUE(table.AddTarget(make_unique<DmTargetLinear>(1, 1, loop_b.device(), 0)));
+    ASSERT_TRUE(table.Emplace<DmTargetLinear>(0, 1, loop_a.device(), 0));
+    ASSERT_TRUE(table.Emplace<DmTargetLinear>(1, 1, loop_b.device(), 0));
     ASSERT_TRUE(table.valid());
 
     TempDevice dev("libdm-test-dm-linear", table);
@@ -141,6 +141,16 @@ TEST(libdm, DmLinear) {
     ASSERT_FALSE(dev.path().empty());
     ASSERT_TRUE(dev.WaitForUdev());
 
+    auto& dm = DeviceMapper::Instance();
+
+    dev_t dev_number;
+    ASSERT_TRUE(dm.GetDeviceNumber(dev.name(), &dev_number));
+    ASSERT_NE(dev_number, 0);
+
+    std::string dev_string;
+    ASSERT_TRUE(dm.GetDeviceString(dev.name(), &dev_string));
+    ASSERT_FALSE(dev_string.empty());
+
     // Note: a scope is needed to ensure that there are no open descriptors
     // when we go to close the device.
     {
@@ -157,7 +167,6 @@ TEST(libdm, DmLinear) {
     }
 
     // Test GetTableStatus.
-    DeviceMapper& dm = DeviceMapper::Instance();
     vector<DeviceMapper::TargetInfo> targets;
     ASSERT_TRUE(dm.GetTableStatus(dev.name(), &targets));
     ASSERT_EQ(targets.size(), 2);
diff --git a/fs_mgr/libdm/include/libdm/dm.h b/fs_mgr/libdm/include/libdm/dm.h
index d7e8aa91c..3d223e37d 100644
--- a/fs_mgr/libdm/include/libdm/dm.h
+++ b/fs_mgr/libdm/include/libdm/dm.h
@@ -20,6 +20,7 @@
 #include <fcntl.h>
 #include <linux/dm-ioctl.h>
 #include <linux/kdev_t.h>
+#include <linux/types.h>
 #include <stdint.h>
 #include <sys/sysmacros.h>
 #include <unistd.h>
@@ -111,6 +112,13 @@ class DeviceMapper final {
     // parameter is not set.
     bool GetDmDevicePathByName(const std::string& name, std::string* path);
 
+    // Returns the dev_t for the named device-mapper node.
+    bool GetDeviceNumber(const std::string& name, dev_t* dev);
+
+    // Returns a major:minor string for the named device-mapper node, that can
+    // be used as inputs to DmTargets that take a block device.
+    bool GetDeviceString(const std::string& name, std::string* dev);
+
     // The only way to create a DeviceMapper object.
     static DeviceMapper& Instance();
 
diff --git a/fs_mgr/libdm/include/libdm/loop_control.h b/fs_mgr/libdm/include/libdm/loop_control.h
index e6e83f40e..6b4c2d8fc 100644
--- a/fs_mgr/libdm/include/libdm/loop_control.h
+++ b/fs_mgr/libdm/include/libdm/loop_control.h
@@ -35,6 +35,9 @@ class LoopControl final {
     // Detach the loop device given by 'loopdev' from the attached backing file.
     bool Detach(const std::string& loopdev) const;
 
+    // Enable Direct I/O on a loop device. This requires kernel 4.9+.
+    static bool EnableDirectIo(int fd);
+
     LoopControl(const LoopControl&) = delete;
     LoopControl& operator=(const LoopControl&) = delete;
     LoopControl& operator=(LoopControl&&) = default;
diff --git a/fs_mgr/libdm/loop_control.cpp b/fs_mgr/libdm/loop_control.cpp
index 0beb1a63e..16bf4b038 100644
--- a/fs_mgr/libdm/loop_control.cpp
+++ b/fs_mgr/libdm/loop_control.cpp
@@ -91,6 +91,27 @@ bool LoopControl::FindFreeLoopDevice(std::string* loopdev) const {
     return true;
 }
 
+bool LoopControl::EnableDirectIo(int fd) {
+#if !defined(LOOP_SET_BLOCK_SIZE)
+    static constexpr int LOOP_SET_BLOCK_SIZE = 0x4C09;
+#endif
+#if !defined(LOOP_SET_DIRECT_IO)
+    static constexpr int LOOP_SET_DIRECT_IO = 0x4C08;
+#endif
+
+    // Note: the block size has to be >= the logical block size of the underlying
+    // block device, *not* the filesystem block size.
+    if (ioctl(fd, LOOP_SET_BLOCK_SIZE, 4096)) {
+        PLOG(ERROR) << "Could not set loop device block size";
+        return false;
+    }
+    if (ioctl(fd, LOOP_SET_DIRECT_IO, 1)) {
+        PLOG(ERROR) << "Could not set loop direct IO";
+        return false;
+    }
+    return true;
+}
+
 LoopDevice::LoopDevice(int fd, bool auto_close) : fd_(fd), owns_fd_(auto_close) {
     Init();
 }