diff --git a/fs_mgr/fs_mgr_format.cpp b/fs_mgr/fs_mgr_format.cpp
index fc88217..85a593f 100644
--- a/fs_mgr/fs_mgr_format.cpp
+++ b/fs_mgr/fs_mgr_format.cpp
@@ -34,23 +34,35 @@
 #include "fs_mgr_priv.h"
 #include "cryptfs.h"
 
-static int format_ext4(char *fs_blkdev, char *fs_mnt_point, bool crypt_footer)
+static int get_dev_sz(char *fs_blkdev, uint64_t *dev_sz)
 {
-    uint64_t dev_sz;
-    int fd, rc = 0;
+    int fd;
 
-    if ((fd = open(fs_blkdev, O_WRONLY)) < 0) {
+    if ((fd = open(fs_blkdev, O_RDONLY)) < 0) {
         PERROR << "Cannot open block device";
         return -1;
     }
 
-    if ((ioctl(fd, BLKGETSIZE64, &dev_sz)) == -1) {
+    if ((ioctl(fd, BLKGETSIZE64, dev_sz)) == -1) {
         PERROR << "Cannot get block device size";
         close(fd);
         return -1;
     }
 
     close(fd);
+    return 0;
+}
+
+static int format_ext4(char *fs_blkdev, char *fs_mnt_point, bool crypt_footer)
+{
+    uint64_t dev_sz;
+    int rc = 0;
+    int status;
+
+    rc = get_dev_sz(fs_blkdev, &dev_sz);
+    if (rc) {
+        return rc;
+    }
 
     /* Format the partition using the calculated length */
     if (crypt_footer) {
@@ -85,9 +97,25 @@
     return rc;
 }
 
-static int format_f2fs(char *fs_blkdev)
+static int format_f2fs(char *fs_blkdev, uint64_t dev_sz, bool crypt_footer)
 {
-    const char* const args[] = {"/system/bin/make_f2fs", "-f", "-O encrypt", fs_blkdev, nullptr};
+    int status;
+
+    if (!dev_sz) {
+        int rc = get_dev_sz(fs_blkdev, &dev_sz);
+        if (rc) {
+            return rc;
+        }
+    }
+
+    /* Format the partition using the calculated length */
+    if (crypt_footer) {
+        dev_sz -= CRYPT_FOOTER_OFFSET;
+    }
+
+    std::string size_str = std::to_string(dev_sz / 4096);
+    const char* const args[] = {
+        "/system/bin/make_f2fs", "-f", "-O", "encrypt", fs_blkdev, size_str.c_str(), nullptr};
 
     return android_fork_execvp_ext(arraysize(args), const_cast<char**>(args), NULL, true,
                                    LOG_KLOG, true, nullptr, nullptr, 0);
@@ -101,7 +129,7 @@
            << " as '" << fstab->fs_type << "'";
 
     if (!strncmp(fstab->fs_type, "f2fs", 4)) {
-        rc = format_f2fs(fstab->blk_device);
+        rc = format_f2fs(fstab->blk_device, fstab->length, crypt_footer);
     } else if (!strncmp(fstab->fs_type, "ext4", 4)) {
         rc = format_ext4(fstab->blk_device, fstab->mount_point, crypt_footer);
     } else {