diff --git a/block/Makefile.objs b/block/Makefile.objs
index 4cf9aa4..e5e54e6 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -2,7 +2,7 @@ block-obj-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat
 block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o qcow2-cache.o
 block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
 block-obj-y += qed-check.o
-block-obj-y += vhdx.o
+block-obj-$(CONFIG_VHDX) += vhdx.o
 block-obj-y += parallels.o blkdebug.o blkverify.o
 block-obj-y += snapshot.o qapi.o
 block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
diff --git a/block/vhdx.c b/block/vhdx.c
index 56bc88e..7bd7c12 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -21,6 +21,7 @@
 #include "qemu/crc32c.h"
 #include "block/vhdx.h"
 
+#include <uuid/uuid.h>
 
 /* Several metadata and region table data entries are identified by
  * guids in  a MS-specific GUID format. */
@@ -156,11 +157,40 @@ typedef struct BDRVVHDXState {
     VHDXBatEntry *bat;
     uint64_t bat_offset;
 
+    MSGUID session_guid;
+
+
     VHDXParentLocatorHeader parent_header;
     VHDXParentLocatorEntry *parent_entries;
 
 } BDRVVHDXState;
 
+/* Calculates new checksum.
+ *
+ * Zero is substituted during crc calculation for the original crc field
+ * crc_offset: byte offset in buf of the buffer crc
+ * buf: buffer pointer
+ * size: size of buffer (must be > crc_offset+4)
+ *
+ * Note: The resulting checksum is in the CPU endianness, not necessarily
+ *       in the file format endianness (LE).  Any header export to disk should
+ *       make sure that vhdx_header_le_export() is used to convert to the
+ *       correct endianness
+ */
+uint32_t vhdx_update_checksum(uint8_t *buf, size_t size, int crc_offset)
+{
+    uint32_t crc;
+
+    assert(buf != NULL);
+    assert(size > (crc_offset + sizeof(crc)));
+
+    memset(buf + crc_offset, 0, sizeof(crc));
+    crc =  crc32c(0xffffffff, buf, size);
+    memcpy(buf + crc_offset, &crc, sizeof(crc));
+
+    return crc;
+}
+
 uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
                             int crc_offset)
 {
@@ -212,6 +242,19 @@ bool vhdx_checksum_is_valid(uint8_t *buf, size_t size, int crc_offset)
 
 
 /*
+ * This generates a UUID that is compliant with the MS GUIDs used
+ * in the VHDX spec (and elsewhere).
+ */
+void vhdx_guid_generate(MSGUID *guid)
+{
+    uuid_t uuid;
+    assert(guid != NULL);
+
+    uuid_generate(uuid);
+    memcpy(guid, uuid, sizeof(MSGUID));
+}
+
+/*
  * Per the MS VHDX Specification, for every VHDX file:
  *      - The header section is fixed size - 1 MB
  *      - The header section is always the first "object"
@@ -249,6 +292,113 @@ static void vhdx_header_le_import(VHDXHeader *h)
     le64_to_cpus(&h->log_offset);
 }
 
+/* All VHDX structures on disk are little endian */
+static void vhdx_header_le_export(VHDXHeader *orig_h, VHDXHeader *new_h)
+{
+    assert(orig_h != NULL);
+    assert(new_h != NULL);
+
+    new_h->signature       = cpu_to_le32(orig_h->signature);
+    new_h->checksum        = cpu_to_le32(orig_h->checksum);
+    new_h->sequence_number = cpu_to_le64(orig_h->sequence_number);
+
+    new_h->file_write_guid = orig_h->file_write_guid;
+    new_h->data_write_guid = orig_h->data_write_guid;
+    new_h->log_guid        = orig_h->log_guid;
+
+    cpu_to_leguids(&new_h->file_write_guid);
+    cpu_to_leguids(&new_h->data_write_guid);
+    cpu_to_leguids(&new_h->log_guid);
+
+    new_h->log_version     = cpu_to_le16(orig_h->log_version);
+    new_h->version         = cpu_to_le16(orig_h->version);
+    new_h->log_length      = cpu_to_le32(orig_h->log_length);
+    new_h->log_offset      = cpu_to_le64(orig_h->log_offset);
+}
+
+/* Update the VHDX headers
+ *
+ * This follows the VHDX spec procedures for header updates.
+ *
+ *  - non-current header is updated with largest sequence number
+ */
+static int vhdx_update_header(BlockDriverState *bs, BDRVVHDXState *s,
+                              bool generate_data_write_guid)
+{
+    int ret = 0;
+    int hdr_idx = 0;
+    uint64_t header_offset = VHDX_HEADER1_OFFSET;
+
+    VHDXHeader *active_header;
+    VHDXHeader *inactive_header;
+    VHDXHeader header_le;
+    uint8_t *buffer;
+
+    /* operate on the non-current header */
+    if (s->curr_header == 0) {
+        hdr_idx = 1;
+        header_offset = VHDX_HEADER2_OFFSET;
+    }
+
+    active_header   = s->headers[s->curr_header];
+    inactive_header = s->headers[hdr_idx];
+
+    inactive_header->sequence_number = active_header->sequence_number + 1;
+
+    /* a new file guid must be generated before any file write, including
+     * headers */
+    inactive_header->file_write_guid = s->session_guid;
+
+    /* a new data guid only needs to be generated before any guest-visible
+     * writes (i.e. something observable via virtual disk read) */
+    if (generate_data_write_guid) {
+        vhdx_guid_generate(&inactive_header->data_write_guid);
+    }
+
+    /* the header checksum is not over just the packed size of VHDXHeader,
+     * but rather over the entire 'reserved' range for the header, which is
+     * 4KB (VHDX_HEADER_SIZE). */
+
+    buffer = qemu_blockalign(bs, VHDX_HEADER_SIZE);
+    /* we can't assume the extra reserved bytes are 0 */
+    ret = bdrv_pread(bs->file, header_offset, buffer, VHDX_HEADER_SIZE);
+    if (ret < 0) {
+        goto exit;
+    }
+    /* overwrite the actual VHDXHeader portion */
+    memcpy(buffer, inactive_header, sizeof(VHDXHeader));
+    inactive_header->checksum =
+                        vhdx_update_checksum(buffer, VHDX_HEADER_SIZE,
+                                             offsetof(VHDXHeader, checksum));
+    vhdx_header_le_export(inactive_header, &header_le);
+    ret = bdrv_pwrite_sync(bs->file, header_offset, &header_le,
+                           sizeof(VHDXHeader));
+    if (ret < 0) {
+        goto exit;
+    }
+    s->curr_header = hdr_idx;
+
+exit:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+/*
+ * The VHDX spec calls for header updates to be performed twice, so that both
+ * the current and non-current header have valid info
+ */
+static int vhdx_update_headers(BlockDriverState *bs, BDRVVHDXState *s,
+                               bool generate_data_write_guid)
+{
+    int ret;
+
+    ret = vhdx_update_header(bs, s, generate_data_write_guid);
+    if (ret < 0) {
+        return ret;
+    }
+    ret = vhdx_update_header(bs, s, generate_data_write_guid);
+    return ret;
+}
 
 /* opens the specified header block from the VHDX file header section */
 static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
@@ -739,6 +889,11 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags)
         goto fail;
     }
 
+    /* This is used for any header updates, for the file_write_guid.
+     * The spec dictates that a new value should be used for the first
+     * header update */
+    vhdx_guid_generate(&s->session_guid);
+
     ret = vhdx_parse_header(bs, s);
     if (ret) {
         goto fail;
@@ -801,8 +956,10 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags)
     }
 
     if (flags & BDRV_O_RDWR) {
-        ret = -ENOTSUP;
-        goto fail;
+        ret = vhdx_update_headers(bs, s, false);
+        if (ret < 0) {
+            goto fail;
+        }
     }
 
     /* TODO: differencing files, write */
diff --git a/block/vhdx.h b/block/vhdx.h
index 9eb6b97..403f766 100644
--- a/block/vhdx.h
+++ b/block/vhdx.h
@@ -67,7 +67,7 @@ typedef struct VHDXFileIdentifier {
  * Microsoft is not just 16 bytes though - it is a structure that is defined,
  * so we need to follow it here so that endianness does not trip us up */
 
-typedef struct MSGUID {
+typedef struct QEMU_PACKED MSGUID {
     uint32_t  data1;
     uint16_t  data2;
     uint16_t  data3;
@@ -309,17 +309,27 @@ typedef struct QEMU_PACKED VHDXParentLocatorEntry {
 /* ----- END VHDX SPECIFICATION STRUCTURES ---- */
 
 
+void vhdx_guid_generate(MSGUID *guid);
+
+uint32_t vhdx_update_checksum(uint8_t *buf, size_t size, int crc_offset);
 uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
                             int crc_offset);
 
 bool vhdx_checksum_is_valid(uint8_t *buf, size_t size, int crc_offset);
 
 
-static void leguid_to_cpus(MSGUID *guid)
+static inline void leguid_to_cpus(MSGUID *guid)
 {
     le32_to_cpus(&guid->data1);
     le16_to_cpus(&guid->data2);
     le16_to_cpus(&guid->data3);
 }
 
+static inline void cpu_to_leguids(MSGUID *guid)
+{
+    cpu_to_le32s(&guid->data1);
+    cpu_to_le16s(&guid->data2);
+    cpu_to_le16s(&guid->data3);
+}
+
 #endif
diff --git a/configure b/configure
index 0a55c20..86a74e3 100755
--- a/configure
+++ b/configure
@@ -243,6 +243,7 @@ gtk=""
 gtkabi="2.0"
 tpm="no"
 libssh2=""
+vhdx=""
 
 # parse CC options first
 for opt do
@@ -945,6 +946,10 @@ for opt do
   ;;
   --enable-libssh2) libssh2="yes"
   ;;
+  --enable-vhdx) vhdx="yes"
+  ;;
+  --disable-vhdx) vhdx="no"
+  ;;
   *) echo "ERROR: unknown option $opt"; show_help="yes"
   ;;
   esac
@@ -1159,6 +1164,8 @@ echo "  --gcov=GCOV              use specified gcov [$gcov_tool]"
 echo "  --enable-tpm             enable TPM support"
 echo "  --disable-libssh2        disable ssh block device support"
 echo "  --enable-libssh2         enable ssh block device support"
+echo "  --disable-vhdx           disables support for the Microsoft VHDX image format"
+echo "  --enable-vhdx            enable support for the Microsoft VHDX image format"
 echo ""
 echo "NOTE: The object files are built at the place where configure is launched"
 exit 1
@@ -1970,6 +1977,18 @@ EOF
   fi
 fi
 
+if test "$vhdx" = "yes" ; then
+    if test "$uuid" = "no" ; then
+        error_exit "uuid required for VHDX support"
+    fi
+elif test "$vhdx" != "no" ; then
+    if test "$uuid" = "yes" ; then
+        vhdx=yes
+    else
+        vhdx=no
+    fi
+fi
+
 ##########################################
 # xfsctl() probe, used for raw-posix
 if test "$xfs" != "no" ; then
@@ -3644,6 +3663,7 @@ echo "TPM support       $tpm"
 echo "libssh2 support   $libssh2"
 echo "TPM passthrough   $tpm_passthrough"
 echo "QOM debugging     $qom_cast_debug"
+echo "vhdx              $vhdx"
 
 if test "$sdl_too_old" = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
@@ -4040,6 +4060,10 @@ if test "$virtio_blk_data_plane" = "yes" ; then
   echo 'CONFIG_VIRTIO_BLK_DATA_PLANE=$(CONFIG_VIRTIO)' >> $config_host_mak
 fi
 
+if test "$vhdx" = "yes" ; then
+  echo "CONFIG_VHDX=y" >> $config_host_mak
+fi
+
 # USB host support
 case "$usb" in
 linux)
