diff --git a/fs_mgr/libfiemap_writer/fiemap_writer.cpp b/fs_mgr/libfiemap_writer/fiemap_writer.cpp
index 3d41876..99a1a2f 100644
--- a/fs_mgr/libfiemap_writer/fiemap_writer.cpp
+++ b/fs_mgr/libfiemap_writer/fiemap_writer.cpp
@@ -618,7 +618,6 @@
 
     fmap->file_path_ = abs_path;
     fmap->bdev_path_ = bdev_path;
-    fmap->file_fd_ = std::move(file_fd);
     fmap->file_size_ = file_size;
     fmap->bdev_size_ = bdevsz;
     fmap->fs_type_ = fs_type;
diff --git a/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp b/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp
index ab4efae..66eb9ae 100644
--- a/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp
+++ b/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp
@@ -38,6 +38,9 @@
 
 #include "utility.h"
 
+namespace android {
+namespace fiemap_writer {
+
 using namespace std;
 using namespace std::string_literals;
 using namespace android::fiemap_writer;
@@ -234,6 +237,105 @@
     ASSERT_EQ(errno, ENOENT);
 }
 
+static string ReadSplitFiles(const std::string& base_path, size_t num_files) {
+    std::string result;
+    for (int i = 0; i < num_files; i++) {
+        std::string path = base_path + android::base::StringPrintf(".%04d", i);
+        std::string data;
+        if (!android::base::ReadFileToString(path, &data)) {
+            return {};
+        }
+        result += data;
+    }
+    return result;
+}
+
+TEST_F(SplitFiemapTest, WriteWholeFile) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+    ASSERT_TRUE(ptr->Write(buffer.get(), kSize));
+
+    std::string expected(reinterpret_cast<char*>(buffer.get()), kSize);
+    auto actual = ReadSplitFiles(testfile, 3);
+    ASSERT_EQ(expected.size(), actual.size());
+    EXPECT_EQ(memcmp(expected.data(), actual.data(), actual.size()), 0);
+}
+
+TEST_F(SplitFiemapTest, WriteFileInChunks1) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+
+    // Write in chunks of 1000 (so some writes straddle the boundary of two
+    // files).
+    size_t bytes_written = 0;
+    while (bytes_written < kSize) {
+        size_t to_write = std::min(kSize - bytes_written, (size_t)1000);
+        char* data = reinterpret_cast<char*>(buffer.get()) + bytes_written;
+        ASSERT_TRUE(ptr->Write(data, to_write));
+        bytes_written += to_write;
+    }
+
+    std::string expected(reinterpret_cast<char*>(buffer.get()), kSize);
+    auto actual = ReadSplitFiles(testfile, 3);
+    ASSERT_EQ(expected.size(), actual.size());
+    EXPECT_EQ(memcmp(expected.data(), actual.data(), actual.size()), 0);
+}
+
+TEST_F(SplitFiemapTest, WriteFileInChunks2) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+
+    // Write in chunks of 32KiB so every write is exactly at the end of the
+    // current file.
+    size_t bytes_written = 0;
+    while (bytes_written < kSize) {
+        size_t to_write = std::min(kSize - bytes_written, kChunkSize);
+        char* data = reinterpret_cast<char*>(buffer.get()) + bytes_written;
+        ASSERT_TRUE(ptr->Write(data, to_write));
+        bytes_written += to_write;
+    }
+
+    std::string expected(reinterpret_cast<char*>(buffer.get()), kSize);
+    auto actual = ReadSplitFiles(testfile, 3);
+    ASSERT_EQ(expected.size(), actual.size());
+    EXPECT_EQ(memcmp(expected.data(), actual.data(), actual.size()), 0);
+}
+
+TEST_F(SplitFiemapTest, WritePastEnd) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+    ASSERT_TRUE(ptr->Write(buffer.get(), kSize));
+    ASSERT_FALSE(ptr->Write(buffer.get(), kSize));
+}
+
 class VerifyBlockWritesExt4 : public ::testing::Test {
     // 2GB Filesystem and 4k block size by default
     static constexpr uint64_t block_size = 4096;
@@ -333,6 +435,11 @@
     return true;
 }
 
+}  // namespace fiemap_writer
+}  // namespace android
+
+using namespace android::fiemap_writer;
+
 int main(int argc, char** argv) {
     ::testing::InitGoogleTest(&argc, argv);
     if (argc <= 1) {
diff --git a/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h b/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h
index 831bc75..9486122 100644
--- a/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h
+++ b/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h
@@ -88,9 +88,6 @@
     // Block device on which we have created the file.
     std::string bdev_path_;
 
-    // File descriptors for the file and block device
-    ::android::base::unique_fd file_fd_;
-
     // Size in bytes of the file this class is writing
     uint64_t file_size_;
 
diff --git a/fs_mgr/libfiemap_writer/include/libfiemap_writer/split_fiemap_writer.h b/fs_mgr/libfiemap_writer/include/libfiemap_writer/split_fiemap_writer.h
index 765cc84..07f3c10 100644
--- a/fs_mgr/libfiemap_writer/include/libfiemap_writer/split_fiemap_writer.h
+++ b/fs_mgr/libfiemap_writer/include/libfiemap_writer/split_fiemap_writer.h
@@ -23,6 +23,8 @@
 #include <string>
 #include <vector>
 
+#include <android-base/unique_fd.h>
+
 #include "fiemap_writer.h"
 
 namespace android {
@@ -54,6 +56,16 @@
     // this returns true and does not report an error.
     static bool RemoveSplitFiles(const std::string& file_path, std::string* message = nullptr);
 
+    // Return whether all components of a split file still have pinned extents.
+    bool HasPinnedExtents() const;
+
+    // Helper method for writing data that spans files. Note there is no seek
+    // method (yet); this starts at 0 and increments the position by |bytes|.
+    bool Write(const void* data, uint64_t bytes);
+
+    // Flush all writes to all split files.
+    bool Flush();
+
     const std::vector<struct fiemap_extent>& extents();
     uint32_t block_size() const;
     uint64_t size() const { return total_size_; }
@@ -73,6 +85,11 @@
     std::vector<FiemapUniquePtr> files_;
     std::vector<struct fiemap_extent> extents_;
     uint64_t total_size_ = 0;
+
+    // Most recently open file and position for Write().
+    size_t cursor_index_ = 0;
+    uint64_t cursor_file_pos_ = 0;
+    android::base::unique_fd cursor_fd_;
 };
 
 }  // namespace fiemap_writer
diff --git a/fs_mgr/libfiemap_writer/split_fiemap_writer.cpp b/fs_mgr/libfiemap_writer/split_fiemap_writer.cpp
index 1f80370..dbb67a8 100644
--- a/fs_mgr/libfiemap_writer/split_fiemap_writer.cpp
+++ b/fs_mgr/libfiemap_writer/split_fiemap_writer.cpp
@@ -176,6 +176,15 @@
     return ok;
 }
 
+bool SplitFiemap::HasPinnedExtents() const {
+    for (const auto& file : files_) {
+        if (!FiemapWriter::HasPinnedExtents(file->file_path())) {
+            return false;
+        }
+    }
+    return true;
+}
+
 const std::vector<struct fiemap_extent>& SplitFiemap::extents() {
     if (extents_.empty()) {
         for (const auto& file : files_) {
@@ -186,6 +195,76 @@
     return extents_;
 }
 
+bool SplitFiemap::Write(const void* data, uint64_t bytes) {
+    // Open the current file.
+    FiemapWriter* file = files_[cursor_index_].get();
+
+    const uint8_t* data_ptr = reinterpret_cast<const uint8_t*>(data);
+    uint64_t bytes_remaining = bytes;
+    while (bytes_remaining) {
+        // How many bytes can we write into the current file?
+        uint64_t file_bytes_left = file->size() - cursor_file_pos_;
+        if (!file_bytes_left) {
+            if (cursor_index_ == files_.size() - 1) {
+                LOG(ERROR) << "write past end of file requested";
+                return false;
+            }
+
+            // No space left in the current file, but we have more files to
+            // use, so prep the next one.
+            cursor_fd_ = {};
+            cursor_file_pos_ = 0;
+            file = files_[++cursor_index_].get();
+            file_bytes_left = file->size();
+        }
+
+        // Open the current file if it's not open.
+        if (cursor_fd_ < 0) {
+            cursor_fd_.reset(open(file->file_path().c_str(), O_CLOEXEC | O_WRONLY));
+            if (cursor_fd_ < 0) {
+                PLOG(ERROR) << "open failed: " << file->file_path();
+                return false;
+            }
+            CHECK(cursor_file_pos_ == 0);
+        }
+
+        if (!FiemapWriter::HasPinnedExtents(file->file_path())) {
+            LOG(ERROR) << "file is no longer pinned: " << file->file_path();
+            return false;
+        }
+
+        uint64_t bytes_to_write = std::min(file_bytes_left, bytes_remaining);
+        if (!android::base::WriteFully(cursor_fd_, data_ptr, bytes_to_write)) {
+            PLOG(ERROR) << "write failed: " << file->file_path();
+            return false;
+        }
+        data_ptr += bytes_to_write;
+        bytes_remaining -= bytes_to_write;
+        cursor_file_pos_ += bytes_to_write;
+    }
+
+    // If we've reached the end of the current file, close it for sanity.
+    if (cursor_file_pos_ == file->size()) {
+        cursor_fd_ = {};
+    }
+    return true;
+}
+
+bool SplitFiemap::Flush() {
+    for (const auto& file : files_) {
+        unique_fd fd(open(file->file_path().c_str(), O_RDONLY | O_CLOEXEC));
+        if (fd < 0) {
+            PLOG(ERROR) << "open failed: " << file->file_path();
+            return false;
+        }
+        if (fsync(fd)) {
+            PLOG(ERROR) << "fsync failed: " << file->file_path();
+            return false;
+        }
+    }
+    return true;
+}
+
 SplitFiemap::~SplitFiemap() {
     if (!creating_) {
         return;
diff --git a/trusty/storage/proxy/proxy.c b/trusty/storage/proxy/proxy.c
index 9a71ae3..c61f7d0 100644
--- a/trusty/storage/proxy/proxy.c
+++ b/trusty/storage/proxy/proxy.c
@@ -39,15 +39,29 @@
 static const char* rpmb_devname;
 static const char* ss_srv_name = STORAGE_DISK_PROXY_PORT;
 
-static const char* _sopts = "hp:d:r:";
+static enum dev_type dev_type = MMC_RPMB;
+
+static enum dev_type parse_dev_type(const char* dev_type_name) {
+    if (!strcmp(dev_type_name, "mmc")) {
+        return MMC_RPMB;
+    } else if (!strcmp(dev_type_name, "virt")) {
+        return VIRT_RPMB;
+    } else {
+        return UNKNOWN_RPMB;
+    }
+}
+
+static const char* _sopts = "hp:d:r:t:";
 static const struct option _lopts[] = {{"help", no_argument, NULL, 'h'},
                                        {"trusty_dev", required_argument, NULL, 'd'},
                                        {"data_path", required_argument, NULL, 'p'},
                                        {"rpmb_dev", required_argument, NULL, 'r'},
+                                       {"dev_type", required_argument, NULL, 't'},
                                        {0, 0, 0, 0}};
 
 static void show_usage_and_exit(int code) {
-    ALOGE("usage: storageproxyd -d <trusty_dev> -p <data_path> -r <rpmb_dev>\n");
+    ALOGE("usage: storageproxyd -d <trusty_dev> -p <data_path> -r <rpmb_dev> -t <dev_type>\n");
+    ALOGE("Available dev types: mmc, virt\n");
     exit(code);
 }
 
@@ -195,6 +209,14 @@
                 rpmb_devname = strdup(optarg);
                 break;
 
+            case 't':
+                dev_type = parse_dev_type(optarg);
+                if (dev_type == UNKNOWN_RPMB) {
+                    ALOGE("Unrecognized dev type: %s\n", optarg);
+                    show_usage_and_exit(EXIT_FAILURE);
+                }
+                break;
+
             default:
                 ALOGE("unrecognized option (%c):\n", opt);
                 show_usage_and_exit(EXIT_FAILURE);
@@ -226,7 +248,7 @@
     if (rc < 0) return EXIT_FAILURE;
 
     /* open rpmb device */
-    rc = rpmb_open(rpmb_devname);
+    rc = rpmb_open(rpmb_devname, dev_type);
     if (rc < 0) return EXIT_FAILURE;
 
     /* connect to Trusty secure storage server */
diff --git a/trusty/storage/proxy/rpmb.c b/trusty/storage/proxy/rpmb.c
index e706d0a..29827e2 100644
--- a/trusty/storage/proxy/rpmb.c
+++ b/trusty/storage/proxy/rpmb.c
@@ -51,6 +51,7 @@
 
 static int rpmb_fd = -1;
 static uint8_t read_buf[4096];
+static enum dev_type dev_type = UNKNOWN_RPMB;
 
 #ifdef RPMB_DEBUG
 
@@ -68,36 +69,16 @@
 
 #endif
 
-int rpmb_send(struct storage_msg* msg, const void* r, size_t req_len) {
-    int rc;
+static int send_mmc_rpmb_req(int mmc_fd, const struct storage_rpmb_send_req* req) {
     struct {
         struct mmc_ioc_multi_cmd multi;
         struct mmc_ioc_cmd cmd_buf[3];
     } mmc = {};
     struct mmc_ioc_cmd* cmd = mmc.multi.cmds;
-    const struct storage_rpmb_send_req* req = r;
-
-    if (req_len < sizeof(*req)) {
-        ALOGW("malformed rpmb request: invalid length (%zu < %zu)\n", req_len, sizeof(*req));
-        msg->result = STORAGE_ERR_NOT_VALID;
-        goto err_response;
-    }
-
-    size_t expected_len = sizeof(*req) + req->reliable_write_size + req->write_size;
-    if (req_len != expected_len) {
-        ALOGW("malformed rpmb request: invalid length (%zu != %zu)\n", req_len, expected_len);
-        msg->result = STORAGE_ERR_NOT_VALID;
-        goto err_response;
-    }
+    int rc;
 
     const uint8_t* write_buf = req->payload;
     if (req->reliable_write_size) {
-        if ((req->reliable_write_size % MMC_BLOCK_SIZE) != 0) {
-            ALOGW("invalid reliable write size %u\n", req->reliable_write_size);
-            msg->result = STORAGE_ERR_NOT_VALID;
-            goto err_response;
-        }
-
         cmd->write_flag = MMC_WRITE_FLAG_RELW;
         cmd->opcode = MMC_WRITE_MULTIPLE_BLOCK;
         cmd->flags = MMC_RSP_SPI_R1 | MMC_RSP_R1 | MMC_CMD_ADTC;
@@ -114,12 +95,6 @@
     }
 
     if (req->write_size) {
-        if ((req->write_size % MMC_BLOCK_SIZE) != 0) {
-            ALOGW("invalid write size %u\n", req->write_size);
-            msg->result = STORAGE_ERR_NOT_VALID;
-            goto err_response;
-        }
-
         cmd->write_flag = MMC_WRITE_FLAG_W;
         cmd->opcode = MMC_WRITE_MULTIPLE_BLOCK;
         cmd->flags = MMC_RSP_SPI_R1 | MMC_RSP_R1 | MMC_CMD_ADTC;
@@ -136,12 +111,6 @@
     }
 
     if (req->read_size) {
-        if (req->read_size % MMC_BLOCK_SIZE != 0 || req->read_size > sizeof(read_buf)) {
-            ALOGE("%s: invalid read size %u\n", __func__, req->read_size);
-            msg->result = STORAGE_ERR_NOT_VALID;
-            goto err_response;
-        }
-
         cmd->write_flag = MMC_WRITE_FLAG_R;
         cmd->opcode = MMC_READ_MULTIPLE_BLOCK;
         cmd->flags = MMC_RSP_SPI_R1 | MMC_RSP_R1 | MMC_CMD_ADTC, cmd->blksz = MMC_BLOCK_SIZE;
@@ -154,9 +123,92 @@
         cmd++;
     }
 
-    rc = ioctl(rpmb_fd, MMC_IOC_MULTI_CMD, &mmc.multi);
+    rc = ioctl(mmc_fd, MMC_IOC_MULTI_CMD, &mmc.multi);
     if (rc < 0) {
         ALOGE("%s: mmc ioctl failed: %d, %s\n", __func__, rc, strerror(errno));
+    }
+    return rc;
+}
+
+static int send_virt_rpmb_req(int rpmb_fd, void* read_buf, size_t read_size, const void* payload,
+                              size_t payload_size) {
+    int rc;
+    uint16_t res_count = read_size / MMC_BLOCK_SIZE;
+    uint16_t cmd_count = payload_size / MMC_BLOCK_SIZE;
+    rc = write(rpmb_fd, &res_count, sizeof(res_count));
+    if (rc < 0) {
+        return rc;
+    }
+    rc = write(rpmb_fd, &cmd_count, sizeof(cmd_count));
+    if (rc < 0) {
+        return rc;
+    }
+    rc = write(rpmb_fd, payload, payload_size);
+    if (rc < 0) {
+        return rc;
+    }
+    rc = read(rpmb_fd, read_buf, read_size);
+    return rc;
+}
+
+int rpmb_send(struct storage_msg* msg, const void* r, size_t req_len) {
+    int rc;
+    const struct storage_rpmb_send_req* req = r;
+
+    if (req_len < sizeof(*req)) {
+        ALOGW("malformed rpmb request: invalid length (%zu < %zu)\n", req_len, sizeof(*req));
+        msg->result = STORAGE_ERR_NOT_VALID;
+        goto err_response;
+    }
+
+    size_t expected_len = sizeof(*req) + req->reliable_write_size + req->write_size;
+    if (req_len != expected_len) {
+        ALOGW("malformed rpmb request: invalid length (%zu != %zu)\n", req_len, expected_len);
+        msg->result = STORAGE_ERR_NOT_VALID;
+        goto err_response;
+    }
+
+    if ((req->reliable_write_size % MMC_BLOCK_SIZE) != 0) {
+        ALOGW("invalid reliable write size %u\n", req->reliable_write_size);
+        msg->result = STORAGE_ERR_NOT_VALID;
+        goto err_response;
+    }
+
+    if ((req->write_size % MMC_BLOCK_SIZE) != 0) {
+        ALOGW("invalid write size %u\n", req->write_size);
+        msg->result = STORAGE_ERR_NOT_VALID;
+        goto err_response;
+    }
+
+    if (req->read_size % MMC_BLOCK_SIZE != 0 || req->read_size > sizeof(read_buf)) {
+        ALOGE("%s: invalid read size %u\n", __func__, req->read_size);
+        msg->result = STORAGE_ERR_NOT_VALID;
+        goto err_response;
+    }
+
+    if (dev_type == MMC_RPMB) {
+        rc = send_mmc_rpmb_req(rpmb_fd, req);
+        if (rc < 0) {
+            msg->result = STORAGE_ERR_GENERIC;
+            goto err_response;
+        }
+    } else if (dev_type == VIRT_RPMB) {
+        size_t payload_size = req->reliable_write_size + req->write_size;
+        rc = send_virt_rpmb_req(rpmb_fd, read_buf, req->read_size, req->payload, payload_size);
+        if (rc < 0) {
+            ALOGE("send_virt_rpmb_req failed: %d, %s\n", rc, strerror(errno));
+            msg->result = STORAGE_ERR_GENERIC;
+            goto err_response;
+        }
+        if (rc != req->read_size) {
+            ALOGE("send_virt_rpmb_req got incomplete response: "
+                  "(size %d, expected %d)\n",
+                  rc, req->read_size);
+            msg->result = STORAGE_ERR_GENERIC;
+            goto err_response;
+        }
+    } else {
+        ALOGE("Unsupported dev_type\n");
         msg->result = STORAGE_ERR_GENERIC;
         goto err_response;
     }
@@ -178,8 +230,9 @@
     return ipc_respond(msg, NULL, 0);
 }
 
-int rpmb_open(const char* rpmb_devname) {
+int rpmb_open(const char* rpmb_devname, enum dev_type open_dev_type) {
     int rc;
+    dev_type = open_dev_type;
 
     rc = open(rpmb_devname, O_RDWR, 0);
     if (rc < 0) {
diff --git a/trusty/storage/proxy/rpmb.h b/trusty/storage/proxy/rpmb.h
index 5107361..4c330c9 100644
--- a/trusty/storage/proxy/rpmb.h
+++ b/trusty/storage/proxy/rpmb.h
@@ -18,6 +18,8 @@
 #include <stdint.h>
 #include <trusty/interface/storage.h>
 
-int rpmb_open(const char* rpmb_devname);
+enum dev_type { UNKNOWN_RPMB, MMC_RPMB, VIRT_RPMB };
+
+int rpmb_open(const char* rpmb_devname, enum dev_type dev_type);
 int rpmb_send(struct storage_msg* msg, const void* r, size_t req_len);
 void rpmb_close(void);