diff --git a/applypatch/applypatch.cpp b/applypatch/applypatch.cpp
index 0268633..2446b2a 100644
--- a/applypatch/applypatch.cpp
+++ b/applypatch/applypatch.cpp
@@ -43,6 +43,7 @@
                           const uint8_t target_sha1[SHA_DIGEST_SIZE],
                           size_t target_size,
                           const Value* bonus_data);
+static std::string short_sha1(const uint8_t sha1[SHA_DIGEST_SIZE]);
 
 static bool mtd_partitions_scanned = false;
 
@@ -461,7 +462,7 @@
                 }
 
                 if (start == len) {
-                    printf("verification read succeeded (attempt %d)\n", attempt+1);
+                    printf("verification read succeeded (attempt %zu)\n", attempt+1);
                     success = true;
                     break;
                 }
@@ -628,12 +629,14 @@
     }
 }
 
-static void print_short_sha1(const uint8_t sha1[SHA_DIGEST_SIZE]) {
+static std::string short_sha1(const uint8_t sha1[SHA_DIGEST_SIZE]) {
     const char* hex = "0123456789abcdef";
+    std::string result = "";
     for (size_t i = 0; i < 4; ++i) {
-        putchar(hex[(sha1[i]>>4) & 0xf]);
-        putchar(hex[sha1[i] & 0xf]);
+        result.push_back(hex[(sha1[i]>>4) & 0xf]);
+        result.push_back(hex[sha1[i] & 0xf]);
     }
+    return result;
 }
 
 // This function applies binary patches to files in a way that is safe
@@ -648,7 +651,7 @@
 //   entries in <patch_sha1_str>, the corresponding patch from
 //   <patch_data> (which must be a VAL_BLOB) is applied to produce a
 //   new file (the type of patch is automatically detected from the
-//   blob daat).  If that new file has sha1 hash <target_sha1_str>,
+//   blob data).  If that new file has sha1 hash <target_sha1_str>,
 //   moves it to replace <target_filename>, and exits successfully.
 //   Note that if <source_filename> and <target_filename> are not the
 //   same, <source_filename> is NOT deleted on success.
@@ -659,7 +662,7 @@
 //   status.
 //
 // <source_filename> may refer to a partition to read the source data.
-// See the comments for the LoadPartition Contents() function above
+// See the comments for the LoadPartitionContents() function above
 // for the format of such a filename.
 
 int applypatch(const char* source_filename,
@@ -694,9 +697,7 @@
         if (memcmp(source_file.sha1, target_sha1, SHA_DIGEST_SIZE) == 0) {
             // The early-exit case:  the patch was already applied, this file
             // has the desired hash, nothing for us to do.
-            printf("already ");
-            print_short_sha1(target_sha1);
-            putchar('\n');
+            printf("already %s\n", short_sha1(target_sha1).c_str());
             free(source_file.data);
             return 0;
         }
@@ -753,6 +754,67 @@
     return result;
 }
 
+/*
+ * This function flashes a given image to the target partition. It verifies
+ * the target cheksum first, and will return if target has the desired hash.
+ * It checks the checksum of the given source image before flashing, and
+ * verifies the target partition afterwards. The function is idempotent.
+ * Returns zero on success.
+ */
+int applypatch_flash(const char* source_filename, const char* target_filename,
+                     const char* target_sha1_str, size_t target_size) {
+    printf("flash %s: ", target_filename);
+
+    uint8_t target_sha1[SHA_DIGEST_SIZE];
+    if (ParseSha1(target_sha1_str, target_sha1) != 0) {
+        printf("failed to parse tgt-sha1 \"%s\"\n", target_sha1_str);
+        return 1;
+    }
+
+    FileContents source_file;
+    source_file.data = NULL;
+    std::string target_str(target_filename);
+
+    std::vector<std::string> pieces = android::base::Split(target_str, ":");
+    if (pieces.size() != 2 || (pieces[0] != "MTD" && pieces[0] != "EMMC")) {
+        printf("invalid target name \"%s\"", target_filename);
+        return 1;
+    }
+
+    // Load the target into the source_file object to see if already applied.
+    pieces.push_back(std::to_string(target_size));
+    pieces.push_back(target_sha1_str);
+    std::string fullname = android::base::Join(pieces, ':');
+    if (LoadPartitionContents(fullname.c_str(), &source_file) == 0 &&
+        memcmp(source_file.sha1, target_sha1, SHA_DIGEST_SIZE) == 0) {
+        // The early-exit case: the image was already applied, this partition
+        // has the desired hash, nothing for us to do.
+        printf("already %s\n", short_sha1(target_sha1).c_str());
+        free(source_file.data);
+        return 0;
+    }
+
+    if (LoadFileContents(source_filename, &source_file) == 0) {
+        if (memcmp(source_file.sha1, target_sha1, SHA_DIGEST_SIZE) != 0) {
+            // The source doesn't have desired checksum.
+            printf("source \"%s\" doesn't have expected sha1 sum\n", source_filename);
+            printf("expected: %s, found: %s\n", short_sha1(target_sha1).c_str(),
+                    short_sha1(source_file.sha1).c_str());
+            free(source_file.data);
+            return 1;
+        }
+    }
+
+    if (WriteToPartition(source_file.data, target_size, target_filename) != 0) {
+        printf("write of copied data to %s failed\n", target_filename);
+        free(source_file.data);
+        return 1;
+    }
+
+    free(source_file.data);
+    return 0;
+}
+
 static int GenerateTarget(FileContents* source_file,
                           const Value* source_patch_value,
                           FileContents* copy_file,
@@ -953,9 +1015,7 @@
         printf("patch did not produce expected sha1\n");
         return 1;
     } else {
-        printf("now ");
-        print_short_sha1(target_sha1);
-        putchar('\n');
+        printf("now %s\n", short_sha1(target_sha1).c_str());
     }
 
     if (output < 0) {
diff --git a/applypatch/applypatch.h b/applypatch/applypatch.h
index edec848..415bc1b 100644
--- a/applypatch/applypatch.h
+++ b/applypatch/applypatch.h
@@ -48,6 +48,8 @@
 int CacheSizeCheck(size_t bytes);
 int ParseSha1(const char* str, uint8_t* digest);
 
+int applypatch_flash(const char* source_filename, const char* target_filename,
+                     const char* target_sha1_str, size_t target_size);
 int applypatch(const char* source_filename,
                const char* target_filename,
                const char* target_sha1_str,
diff --git a/applypatch/main.cpp b/applypatch/main.cpp
index 63ff5c2..966d8b9 100644
--- a/applypatch/main.cpp
+++ b/applypatch/main.cpp
@@ -47,8 +47,8 @@
 // "<sha1>:<filename>" into the new parallel arrays *sha1s and
 // *patches (loading file contents into the patches).  Returns true on
 // success.
-static bool ParsePatchArgs(int argc, char** argv,
-                          char*** sha1s, Value*** patches, int* num_patches) {
+static bool ParsePatchArgs(int argc, char** argv, char*** sha1s,
+                           Value*** patches, int* num_patches) {
     *num_patches = argc;
     *sha1s = reinterpret_cast<char**>(malloc(*num_patches * sizeof(char*)));
     *patches = reinterpret_cast<Value**>(malloc(*num_patches * sizeof(Value*)));
@@ -98,7 +98,12 @@
     return false;
 }
 
-int PatchMode(int argc, char** argv) {
+static int FlashMode(const char* src_filename, const char* tgt_filename,
+                     const char* tgt_sha1, size_t tgt_size) {
+    return applypatch_flash(src_filename, tgt_filename, tgt_sha1, tgt_size);
+}
+
+static int PatchMode(int argc, char** argv) {
     Value* bonus = NULL;
     if (argc >= 3 && strcmp(argv[1], "-b") == 0) {
         FileContents fc;
@@ -114,7 +119,7 @@
         argv += 2;
     }
 
-    if (argc < 6) {
+    if (argc < 4) {
         return 2;
     }
 
@@ -125,6 +130,16 @@
         return 1;
     }
 
+    // If no <src-sha1>:<patch> is provided, it is in flash mode.
+    if (argc == 5) {
+        if (bonus != NULL) {
+            printf("bonus file not supported in flash mode\n");
+            return 1;
+        }
+        return FlashMode(argv[1], argv[2], argv[3], target_size);
+    }
+
+
     char** sha1s;
     Value** patches;
     int num_patches;
@@ -162,6 +177,10 @@
 // - if the sha1 hash of <tgt-file> is <tgt-sha1>, does nothing and exits
 //   successfully.
 //
+// - otherwise, if no <src-sha1>:<patch> is provided, flashes <tgt-file> with
+//   <src-file>. <tgt-file> must be a partition name, while <src-file> must
+//   be a regular image file. <src-file> will not be deleted on success.
+//
 // - otherwise, if the sha1 hash of <src-file> is <src-sha1>, applies the
 //   bsdiff <patch> to <src-file> to produce a new file (the type of patch
 //   is automatically detected from the file header).  If that new