Merge remote-tracking branch 'stefanha/block' into staging

# By Fam Zheng (8) and others
# Via Stefan Hajnoczi
* stefanha/block:
  qemu-iotests: Filter out 'adapter_type'
  nbd: support large NBD requests
  nbd: use g_slice_new() instead of a freelist
  qemu-iotests: Filter out vmdk creation options
  vmdk: add bdrv_co_write_zeroes
  vmdk: store fields of VmdkMetaData in cpu endian
  vmdk: change magic number to macro
  vmdk: Add option to create zeroed-grain image
  vmdk: add support for “zeroed‐grain” GTE
  vmdk: named return code.
  blockdev: Replace "undefined error" in qmp_block_resize
  block: add read-only support to VHDX image format.
  block: initial VHDX driver support framework - supports open and probe
  block: vhdx header for the QEMU support of VHDX images
  qemu: add castagnoli crc32c checksum algorithm

11 files changed, 1618 insertions, 87 deletions

diff --git a/block/Makefile.objs b/block/Makefile.objs
index 6c4b5bc6b..5f0358a3d 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -2,6 +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-y += parallels.o blkdebug.o blkverify.o
 block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
 block-obj-$(CONFIG_POSIX) += raw-posix.o
diff --git a/block/vhdx.c b/block/vhdx.c
new file mode 100644
index 000000000..e9704b1fd
--- /dev/null
+++ b/block/vhdx.c
@@ -0,0 +1,972 @@
+/*
+ * Block driver for Hyper-V VHDX Images
+ *
+ * Copyright (c) 2013 Red Hat, Inc.,
+ *
+ * Authors:
+ *  Jeff Cody <jcody@redhat.com>
+ *
+ *  This is based on the "VHDX Format Specification v0.95", published 4/12/2012
+ *  by Microsoft:
+ *      https://www.microsoft.com/en-us/download/details.aspx?id=29681
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "block/block_int.h"
+#include "qemu/module.h"
+#include "qemu/crc32c.h"
+#include "block/vhdx.h"
+
+
+/* Several metadata and region table data entries are identified by
+ * guids in  a MS-specific GUID format. */
+
+
+/* ------- Known Region Table GUIDs ---------------------- */
+static const MSGUID bat_guid =      { .data1 = 0x2dc27766,
+                                      .data2 = 0xf623,
+                                      .data3 = 0x4200,
+                                      .data4 = { 0x9d, 0x64, 0x11, 0x5e,
+                                                 0x9b, 0xfd, 0x4a, 0x08} };
+
+static const MSGUID metadata_guid = { .data1 = 0x8b7ca206,
+                                      .data2 = 0x4790,
+                                      .data3 = 0x4b9a,
+                                      .data4 = { 0xb8, 0xfe, 0x57, 0x5f,
+                                                 0x05, 0x0f, 0x88, 0x6e} };
+
+
+
+/* ------- Known Metadata Entry GUIDs ---------------------- */
+static const MSGUID file_param_guid =   { .data1 = 0xcaa16737,
+                                          .data2 = 0xfa36,
+                                          .data3 = 0x4d43,
+                                          .data4 = { 0xb3, 0xb6, 0x33, 0xf0,
+                                                     0xaa, 0x44, 0xe7, 0x6b} };
+
+static const MSGUID virtual_size_guid = { .data1 = 0x2FA54224,
+                                          .data2 = 0xcd1b,
+                                          .data3 = 0x4876,
+                                          .data4 = { 0xb2, 0x11, 0x5d, 0xbe,
+                                                     0xd8, 0x3b, 0xf4, 0xb8} };
+
+static const MSGUID page83_guid =       { .data1 = 0xbeca12ab,
+                                          .data2 = 0xb2e6,
+                                          .data3 = 0x4523,
+                                          .data4 = { 0x93, 0xef, 0xc3, 0x09,
+                                                     0xe0, 0x00, 0xc7, 0x46} };
+
+
+static const MSGUID phys_sector_guid =  { .data1 = 0xcda348c7,
+                                          .data2 = 0x445d,
+                                          .data3 = 0x4471,
+                                          .data4 = { 0x9c, 0xc9, 0xe9, 0x88,
+                                                     0x52, 0x51, 0xc5, 0x56} };
+
+static const MSGUID parent_locator_guid = { .data1 = 0xa8d35f2d,
+                                            .data2 = 0xb30b,
+                                            .data3 = 0x454d,
+                                            .data4 = { 0xab, 0xf7, 0xd3,
+                                                       0xd8, 0x48, 0x34,
+                                                       0xab, 0x0c} };
+
+static const MSGUID logical_sector_guid = { .data1 = 0x8141bf1d,
+                                            .data2 = 0xa96f,
+                                            .data3 = 0x4709,
+                                            .data4 = { 0xba, 0x47, 0xf2,
+                                                       0x33, 0xa8, 0xfa,
+                                                       0xab, 0x5f} };
+
+/* Each parent type must have a valid GUID; this is for parent images
+ * of type 'VHDX'.  If we were to allow e.g. a QCOW2 parent, we would
+ * need to make up our own QCOW2 GUID type */
+static const MSGUID parent_vhdx_guid = { .data1 = 0xb04aefb7,
+                                         .data2 = 0xd19e,
+                                         .data3 = 0x4a81,
+                                         .data4 = { 0xb7, 0x89, 0x25, 0xb8,
+                                                    0xe9, 0x44, 0x59, 0x13} };
+
+
+#define META_FILE_PARAMETER_PRESENT      0x01
+#define META_VIRTUAL_DISK_SIZE_PRESENT   0x02
+#define META_PAGE_83_PRESENT             0x04
+#define META_LOGICAL_SECTOR_SIZE_PRESENT 0x08
+#define META_PHYS_SECTOR_SIZE_PRESENT    0x10
+#define META_PARENT_LOCATOR_PRESENT      0x20
+
+#define META_ALL_PRESENT    \
+    (META_FILE_PARAMETER_PRESENT | META_VIRTUAL_DISK_SIZE_PRESENT | \
+     META_PAGE_83_PRESENT | META_LOGICAL_SECTOR_SIZE_PRESENT | \
+     META_PHYS_SECTOR_SIZE_PRESENT)
+
+typedef struct VHDXMetadataEntries {
+    VHDXMetadataTableEntry file_parameters_entry;
+    VHDXMetadataTableEntry virtual_disk_size_entry;
+    VHDXMetadataTableEntry page83_data_entry;
+    VHDXMetadataTableEntry logical_sector_size_entry;
+    VHDXMetadataTableEntry phys_sector_size_entry;
+    VHDXMetadataTableEntry parent_locator_entry;
+    uint16_t present;
+} VHDXMetadataEntries;
+
+
+typedef struct VHDXSectorInfo {
+    uint32_t bat_idx;       /* BAT entry index */
+    uint32_t sectors_avail; /* sectors available in payload block */
+    uint32_t bytes_left;    /* bytes left in the block after data to r/w */
+    uint32_t bytes_avail;   /* bytes available in payload block */
+    uint64_t file_offset;   /* absolute offset in bytes, in file */
+    uint64_t block_offset;  /* block offset, in bytes */
+} VHDXSectorInfo;
+
+
+
+typedef struct BDRVVHDXState {
+    CoMutex lock;
+
+    int curr_header;
+    VHDXHeader *headers[2];
+
+    VHDXRegionTableHeader rt;
+    VHDXRegionTableEntry bat_rt;         /* region table for the BAT */
+    VHDXRegionTableEntry metadata_rt;    /* region table for the metadata */
+
+    VHDXMetadataTableHeader metadata_hdr;
+    VHDXMetadataEntries metadata_entries;
+
+    VHDXFileParameters params;
+    uint32_t block_size;
+    uint32_t block_size_bits;
+    uint32_t sectors_per_block;
+    uint32_t sectors_per_block_bits;
+
+    uint64_t virtual_disk_size;
+    uint32_t logical_sector_size;
+    uint32_t physical_sector_size;
+
+    uint64_t chunk_ratio;
+    uint32_t chunk_ratio_bits;
+    uint32_t logical_sector_size_bits;
+
+    uint32_t bat_entries;
+    VHDXBatEntry *bat;
+    uint64_t bat_offset;
+
+    VHDXParentLocatorHeader parent_header;
+    VHDXParentLocatorEntry *parent_entries;
+
+} BDRVVHDXState;
+
+uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
+                            int crc_offset)
+{
+    uint32_t crc_new;
+    uint32_t crc_orig;
+    assert(buf != NULL);
+
+    if (crc_offset > 0) {
+        memcpy(&crc_orig, buf + crc_offset, sizeof(crc_orig));
+        memset(buf + crc_offset, 0, sizeof(crc_orig));
+    }
+
+    crc_new = crc32c(crc, buf, size);
+    if (crc_offset > 0) {
+        memcpy(buf + crc_offset, &crc_orig, sizeof(crc_orig));
+    }
+
+    return crc_new;
+}
+
+/* Validates the checksum of the buffer, with an in-place CRC.
+ *
+ * Zero is substituted during crc calculation for the original crc field,
+ * and the crc field is restored afterwards.  But the buffer will be modifed
+ * during the calculation, so this may not be not suitable for multi-threaded
+ * use.
+ *
+ * crc_offset: byte offset in buf of the buffer crc
+ * buf: buffer pointer
+ * size: size of buffer (must be > crc_offset+4)
+ *
+ * returns true if checksum is valid, false otherwise
+ */
+bool vhdx_checksum_is_valid(uint8_t *buf, size_t size, int crc_offset)
+{
+    uint32_t crc_orig;
+    uint32_t crc;
+
+    assert(buf != NULL);
+    assert(size > (crc_offset + 4));
+
+    memcpy(&crc_orig, buf + crc_offset, sizeof(crc_orig));
+    crc_orig = le32_to_cpu(crc_orig);
+
+    crc = vhdx_checksum_calc(0xffffffff, buf, size, crc_offset);
+
+    return crc == crc_orig;
+}
+
+
+/*
+ * 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"
+ *      - The first 64KB of the header is the File Identifier
+ *      - The first uint64 (8 bytes) is the VHDX Signature ("vhdxfile")
+ *      - The following 512 bytes constitute a UTF-16 string identifiying the
+ *        software that created the file, and is optional and diagnostic only.
+ *
+ *  Therefore, we probe by looking for the vhdxfile signature "vhdxfile"
+ */
+static int vhdx_probe(const uint8_t *buf, int buf_size, const char *filename)
+{
+    if (buf_size >= 8 && !memcmp(buf, "vhdxfile", 8)) {
+        return 100;
+    }
+    return 0;
+}
+
+/* All VHDX structures on disk are little endian */
+static void vhdx_header_le_import(VHDXHeader *h)
+{
+    assert(h != NULL);
+
+    le32_to_cpus(&h->signature);
+    le32_to_cpus(&h->checksum);
+    le64_to_cpus(&h->sequence_number);
+
+    leguid_to_cpus(&h->file_write_guid);
+    leguid_to_cpus(&h->data_write_guid);
+    leguid_to_cpus(&h->log_guid);
+
+    le16_to_cpus(&h->log_version);
+    le16_to_cpus(&h->version);
+    le32_to_cpus(&h->log_length);
+    le64_to_cpus(&h->log_offset);
+}
+
+
+/* opens the specified header block from the VHDX file header section */
+static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    VHDXHeader *header1;
+    VHDXHeader *header2;
+    bool h1_valid = false;
+    bool h2_valid = false;
+    uint64_t h1_seq = 0;
+    uint64_t h2_seq = 0;
+    uint8_t *buffer;
+
+    header1 = qemu_blockalign(bs, sizeof(VHDXHeader));
+    header2 = qemu_blockalign(bs, sizeof(VHDXHeader));
+
+    buffer = qemu_blockalign(bs, VHDX_HEADER_SIZE);
+
+    s->headers[0] = header1;
+    s->headers[1] = header2;
+
+    /* We have to read the whole VHDX_HEADER_SIZE instead of
+     * sizeof(VHDXHeader), because the checksum is over the whole
+     * region */
+    ret = bdrv_pread(bs->file, VHDX_HEADER1_OFFSET, buffer, VHDX_HEADER_SIZE);
+    if (ret < 0) {
+        goto fail;
+    }
+    /* copy over just the relevant portion that we need */
+    memcpy(header1, buffer, sizeof(VHDXHeader));
+    vhdx_header_le_import(header1);
+
+    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
+        !memcmp(&header1->signature, "head", 4)             &&
+        header1->version == 1) {
+        h1_seq = header1->sequence_number;
+        h1_valid = true;
+    }
+
+    ret = bdrv_pread(bs->file, VHDX_HEADER2_OFFSET, buffer, VHDX_HEADER_SIZE);
+    if (ret < 0) {
+        goto fail;
+    }
+    /* copy over just the relevant portion that we need */
+    memcpy(header2, buffer, sizeof(VHDXHeader));
+    vhdx_header_le_import(header2);
+
+    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
+        !memcmp(&header2->signature, "head", 4)             &&
+        header2->version == 1) {
+        h2_seq = header2->sequence_number;
+        h2_valid = true;
+    }
+
+    /* If there is only 1 valid header (or no valid headers), we
+     * don't care what the sequence numbers are */
+    if (h1_valid && !h2_valid) {
+        s->curr_header = 0;
+    } else if (!h1_valid && h2_valid) {
+        s->curr_header = 1;
+    } else if (!h1_valid && !h2_valid) {
+        ret = -EINVAL;
+        goto fail;
+    } else {
+        /* If both headers are valid, then we choose the active one by the
+         * highest sequence number.  If the sequence numbers are equal, that is
+         * invalid */
+        if (h1_seq > h2_seq) {
+            s->curr_header = 0;
+        } else if (h2_seq > h1_seq) {
+            s->curr_header = 1;
+        } else {
+            ret = -EINVAL;
+            goto fail;
+        }
+    }
+
+    ret = 0;
+
+    goto exit;
+
+fail:
+    qerror_report(ERROR_CLASS_GENERIC_ERROR, "No valid VHDX header found");
+    qemu_vfree(header1);
+    qemu_vfree(header2);
+    s->headers[0] = NULL;
+    s->headers[1] = NULL;
+exit:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+
+static int vhdx_open_region_tables(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    uint8_t *buffer;
+    int offset = 0;
+    VHDXRegionTableEntry rt_entry;
+    uint32_t i;
+    bool bat_rt_found = false;
+    bool metadata_rt_found = false;
+
+    /* We have to read the whole 64KB block, because the crc32 is over the
+     * whole block */
+    buffer = qemu_blockalign(bs, VHDX_HEADER_BLOCK_SIZE);
+
+    ret = bdrv_pread(bs->file, VHDX_REGION_TABLE_OFFSET, buffer,
+                     VHDX_HEADER_BLOCK_SIZE);
+    if (ret < 0) {
+        goto fail;
+    }
+    memcpy(&s->rt, buffer, sizeof(s->rt));
+    le32_to_cpus(&s->rt.signature);
+    le32_to_cpus(&s->rt.checksum);
+    le32_to_cpus(&s->rt.entry_count);
+    le32_to_cpus(&s->rt.reserved);
+    offset += sizeof(s->rt);
+
+    if (!vhdx_checksum_is_valid(buffer, VHDX_HEADER_BLOCK_SIZE, 4) ||
+        memcmp(&s->rt.signature, "regi", 4)) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* Per spec, maximum region table entry count is 2047 */
+    if (s->rt.entry_count > 2047) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    for (i = 0; i < s->rt.entry_count; i++) {
+        memcpy(&rt_entry, buffer + offset, sizeof(rt_entry));
+        offset += sizeof(rt_entry);
+
+        leguid_to_cpus(&rt_entry.guid);
+        le64_to_cpus(&rt_entry.file_offset);
+        le32_to_cpus(&rt_entry.length);
+        le32_to_cpus(&rt_entry.data_bits);
+
+        /* see if we recognize the entry */
+        if (guid_eq(rt_entry.guid, bat_guid)) {
+            /* must be unique; if we have already found it this is invalid */
+            if (bat_rt_found) {
+                ret = -EINVAL;
+                goto fail;
+            }
+            bat_rt_found = true;
+            s->bat_rt = rt_entry;
+            continue;
+        }
+
+        if (guid_eq(rt_entry.guid, metadata_guid)) {
+            /* must be unique; if we have already found it this is invalid */
+            if (metadata_rt_found) {
+                ret = -EINVAL;
+                goto fail;
+            }
+            metadata_rt_found = true;
+            s->metadata_rt = rt_entry;
+            continue;
+        }
+
+        if (rt_entry.data_bits & VHDX_REGION_ENTRY_REQUIRED) {
+            /* cannot read vhdx file - required region table entry that
+             * we do not understand.  per spec, we must fail to open */
+            ret = -ENOTSUP;
+            goto fail;
+        }
+    }
+    ret = 0;
+
+fail:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+
+
+/* Metadata initial parser
+ *
+ * This loads all the metadata entry fields.  This may cause additional
+ * fields to be processed (e.g. parent locator, etc..).
+ *
+ * There are 5 Metadata items that are always required:
+ *      - File Parameters (block size, has a parent)
+ *      - Virtual Disk Size (size, in bytes, of the virtual drive)
+ *      - Page 83 Data (scsi page 83 guid)
+ *      - Logical Sector Size (logical sector size in bytes, either 512 or
+ *                             4096.  We only support 512 currently)
+ *      - Physical Sector Size (512 or 4096)
+ *
+ * Also, if the File Parameters indicate this is a differencing file,
+ * we must also look for the Parent Locator metadata item.
+ */
+static int vhdx_parse_metadata(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    uint8_t *buffer;
+    int offset = 0;
+    uint32_t i = 0;
+    VHDXMetadataTableEntry md_entry;
+
+    buffer = qemu_blockalign(bs, VHDX_METADATA_TABLE_MAX_SIZE);
+
+    ret = bdrv_pread(bs->file, s->metadata_rt.file_offset, buffer,
+                     VHDX_METADATA_TABLE_MAX_SIZE);
+    if (ret < 0) {
+        goto exit;
+    }
+    memcpy(&s->metadata_hdr, buffer, sizeof(s->metadata_hdr));
+    offset += sizeof(s->metadata_hdr);
+
+    le64_to_cpus(&s->metadata_hdr.signature);
+    le16_to_cpus(&s->metadata_hdr.reserved);
+    le16_to_cpus(&s->metadata_hdr.entry_count);
+
+    if (memcmp(&s->metadata_hdr.signature, "metadata", 8)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    s->metadata_entries.present = 0;
+
+    if ((s->metadata_hdr.entry_count * sizeof(md_entry)) >
+        (VHDX_METADATA_TABLE_MAX_SIZE - offset)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    for (i = 0; i < s->metadata_hdr.entry_count; i++) {
+        memcpy(&md_entry, buffer + offset, sizeof(md_entry));
+        offset += sizeof(md_entry);
+
+        leguid_to_cpus(&md_entry.item_id);
+        le32_to_cpus(&md_entry.offset);
+        le32_to_cpus(&md_entry.length);
+        le32_to_cpus(&md_entry.data_bits);
+        le32_to_cpus(&md_entry.reserved2);
+
+        if (guid_eq(md_entry.item_id, file_param_guid)) {
+            if (s->metadata_entries.present & META_FILE_PARAMETER_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.file_parameters_entry = md_entry;
+            s->metadata_entries.present |= META_FILE_PARAMETER_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, virtual_size_guid)) {
+            if (s->metadata_entries.present & META_VIRTUAL_DISK_SIZE_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.virtual_disk_size_entry = md_entry;
+            s->metadata_entries.present |= META_VIRTUAL_DISK_SIZE_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, page83_guid)) {
+            if (s->metadata_entries.present & META_PAGE_83_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.page83_data_entry = md_entry;
+            s->metadata_entries.present |= META_PAGE_83_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, logical_sector_guid)) {
+            if (s->metadata_entries.present &
+                META_LOGICAL_SECTOR_SIZE_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.logical_sector_size_entry = md_entry;
+            s->metadata_entries.present |= META_LOGICAL_SECTOR_SIZE_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, phys_sector_guid)) {
+            if (s->metadata_entries.present & META_PHYS_SECTOR_SIZE_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.phys_sector_size_entry = md_entry;
+            s->metadata_entries.present |= META_PHYS_SECTOR_SIZE_PRESENT;
+            continue;
+        }
+
+        if (guid_eq(md_entry.item_id, parent_locator_guid)) {
+            if (s->metadata_entries.present & META_PARENT_LOCATOR_PRESENT) {
+                ret = -EINVAL;
+                goto exit;
+            }
+            s->metadata_entries.parent_locator_entry = md_entry;
+            s->metadata_entries.present |= META_PARENT_LOCATOR_PRESENT;
+            continue;
+        }
+
+        if (md_entry.data_bits & VHDX_META_FLAGS_IS_REQUIRED) {
+            /* cannot read vhdx file - required region table entry that
+             * we do not understand.  per spec, we must fail to open */
+            ret = -ENOTSUP;
+            goto exit;
+        }
+    }
+
+    if (s->metadata_entries.present != META_ALL_PRESENT) {
+        ret = -ENOTSUP;
+        goto exit;
+    }
+
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.file_parameters_entry.offset
+                                         + s->metadata_rt.file_offset,
+                     &s->params,
+                     sizeof(s->params));
+
+    if (ret < 0) {
+        goto exit;
+    }
+
+    le32_to_cpus(&s->params.block_size);
+    le32_to_cpus(&s->params.data_bits);
+
+
+    /* We now have the file parameters, so we can tell if this is a
+     * differencing file (i.e.. has_parent), is dynamic or fixed
+     * sized (leave_blocks_allocated), and the block size */
+
+    /* The parent locator required iff the file parameters has_parent set */
+    if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
+        if (s->metadata_entries.present & META_PARENT_LOCATOR_PRESENT) {
+            /* TODO: parse  parent locator fields */
+            ret = -ENOTSUP; /* temp, until differencing files are supported */
+            goto exit;
+        } else {
+            /* if has_parent is set, but there is not parent locator present,
+             * then that is an invalid combination */
+            ret = -EINVAL;
+            goto exit;
+        }
+    }
+
+    /* determine virtual disk size, logical sector size,
+     * and phys sector size */
+
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.virtual_disk_size_entry.offset
+                                           + s->metadata_rt.file_offset,
+                     &s->virtual_disk_size,
+                     sizeof(uint64_t));
+    if (ret < 0) {
+        goto exit;
+    }
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.logical_sector_size_entry.offset
+                                             + s->metadata_rt.file_offset,
+                     &s->logical_sector_size,
+                     sizeof(uint32_t));
+    if (ret < 0) {
+        goto exit;
+    }
+    ret = bdrv_pread(bs->file,
+                     s->metadata_entries.phys_sector_size_entry.offset
+                                          + s->metadata_rt.file_offset,
+                     &s->physical_sector_size,
+                     sizeof(uint32_t));
+    if (ret < 0) {
+        goto exit;
+    }
+
+    le64_to_cpus(&s->virtual_disk_size);
+    le32_to_cpus(&s->logical_sector_size);
+    le32_to_cpus(&s->physical_sector_size);
+
+    if (s->logical_sector_size == 0 || s->params.block_size == 0) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    /* both block_size and sector_size are guaranteed powers of 2 */
+    s->sectors_per_block = s->params.block_size / s->logical_sector_size;
+    s->chunk_ratio = (VHDX_MAX_SECTORS_PER_BLOCK) *
+                     (uint64_t)s->logical_sector_size /
+                     (uint64_t)s->params.block_size;
+
+    /* These values are ones we will want to use for division / multiplication
+     * later on, and they are all guaranteed (per the spec) to be powers of 2,
+     * so we can take advantage of that for shift operations during
+     * reads/writes */
+    if (s->logical_sector_size & (s->logical_sector_size - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+    if (s->sectors_per_block & (s->sectors_per_block - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+    if (s->chunk_ratio & (s->chunk_ratio - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+    s->block_size = s->params.block_size;
+    if (s->block_size & (s->block_size - 1)) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    s->logical_sector_size_bits = 31 - clz32(s->logical_sector_size);
+    s->sectors_per_block_bits =   31 - clz32(s->sectors_per_block);
+    s->chunk_ratio_bits =         63 - clz64(s->chunk_ratio);
+    s->block_size_bits =          31 - clz32(s->block_size);
+
+    ret = 0;
+
+exit:
+    qemu_vfree(buffer);
+    return ret;
+}
+
+/* Parse the replay log.  Per the VHDX spec, if the log is present
+ * it must be replayed prior to opening the file, even read-only.
+ *
+ * If read-only, we must replay the log in RAM (or refuse to open
+ * a dirty VHDX file read-only */
+static int vhdx_parse_log(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    int i;
+    VHDXHeader *hdr;
+
+    hdr = s->headers[s->curr_header];
+
+    /* either the log guid, or log length is zero,
+     * then a replay log is present */
+    for (i = 0; i < sizeof(hdr->log_guid.data4); i++) {
+        ret |= hdr->log_guid.data4[i];
+    }
+    if (hdr->log_guid.data1 == 0 &&
+        hdr->log_guid.data2 == 0 &&
+        hdr->log_guid.data3 == 0 &&
+        ret == 0) {
+        goto exit;
+    }
+
+    /* per spec, only log version of 0 is supported */
+    if (hdr->log_version != 0) {
+        ret = -EINVAL;
+        goto exit;
+    }
+
+    if (hdr->log_length == 0) {
+        goto exit;
+    }
+
+    /* We currently do not support images with logs to replay */
+    ret = -ENOTSUP;
+
+exit:
+    return ret;
+}
+
+
+static int vhdx_open(BlockDriverState *bs, QDict *options, int flags)
+{
+    BDRVVHDXState *s = bs->opaque;
+    int ret = 0;
+    uint32_t i;
+    uint64_t signature;
+    uint32_t data_blocks_cnt, bitmap_blocks_cnt;
+
+
+    s->bat = NULL;
+
+    qemu_co_mutex_init(&s->lock);
+
+    /* validate the file signature */
+    ret = bdrv_pread(bs->file, 0, &signature, sizeof(uint64_t));
+    if (ret < 0) {
+        goto fail;
+    }
+    if (memcmp(&signature, "vhdxfile", 8)) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    ret = vhdx_parse_header(bs, s);
+    if (ret) {
+        goto fail;
+    }
+
+    ret = vhdx_parse_log(bs, s);
+    if (ret) {
+        goto fail;
+    }
+
+    ret = vhdx_open_region_tables(bs, s);
+    if (ret) {
+        goto fail;
+    }
+
+    ret = vhdx_parse_metadata(bs, s);
+    if (ret) {
+        goto fail;
+    }
+    s->block_size = s->params.block_size;
+
+    /* the VHDX spec dictates that virtual_disk_size is always a multiple of
+     * logical_sector_size */
+    bs->total_sectors = s->virtual_disk_size >> s->logical_sector_size_bits;
+
+    data_blocks_cnt = s->virtual_disk_size >> s->block_size_bits;
+    if (s->virtual_disk_size - (data_blocks_cnt << s->block_size_bits)) {
+        data_blocks_cnt++;
+    }
+    bitmap_blocks_cnt = data_blocks_cnt >> s->chunk_ratio_bits;
+    if (data_blocks_cnt - (bitmap_blocks_cnt << s->chunk_ratio_bits)) {
+        bitmap_blocks_cnt++;
+    }
+
+    if (s->parent_entries) {
+        s->bat_entries = bitmap_blocks_cnt * (s->chunk_ratio + 1);
+    } else {
+        s->bat_entries = data_blocks_cnt +
+                         ((data_blocks_cnt - 1) >> s->chunk_ratio_bits);
+    }
+
+    s->bat_offset = s->bat_rt.file_offset;
+
+    if (s->bat_entries > s->bat_rt.length / sizeof(VHDXBatEntry)) {
+        /* BAT allocation is not large enough for all entries */
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    s->bat = qemu_blockalign(bs, s->bat_rt.length);
+
+    ret = bdrv_pread(bs->file, s->bat_offset, s->bat, s->bat_rt.length);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    for (i = 0; i < s->bat_entries; i++) {
+        le64_to_cpus(&s->bat[i]);
+    }
+
+    if (flags & BDRV_O_RDWR) {
+        ret = -ENOTSUP;
+        goto fail;
+    }
+
+    /* TODO: differencing files, write */
+
+    return 0;
+fail:
+    qemu_vfree(s->headers[0]);
+    qemu_vfree(s->headers[1]);
+    qemu_vfree(s->bat);
+    qemu_vfree(s->parent_entries);
+    return ret;
+}
+
+static int vhdx_reopen_prepare(BDRVReopenState *state,
+                               BlockReopenQueue *queue, Error **errp)
+{
+    return 0;
+}
+
+
+/*
+ * Perform sector to block offset translations, to get various
+ * sector and file offsets into the image.  See VHDXSectorInfo
+ */
+static void vhdx_block_translate(BDRVVHDXState *s, int64_t sector_num,
+                                 int nb_sectors, VHDXSectorInfo *sinfo)
+{
+    uint32_t block_offset;
+
+    sinfo->bat_idx = sector_num >> s->sectors_per_block_bits;
+    /* effectively a modulo - this gives us the offset into the block
+     * (in sector sizes) for our sector number */
+    block_offset = sector_num - (sinfo->bat_idx << s->sectors_per_block_bits);
+    /* the chunk ratio gives us the interleaving of the sector
+     * bitmaps, so we need to advance our page block index by the
+     * sector bitmaps entry number */
+    sinfo->bat_idx += sinfo->bat_idx >> s->chunk_ratio_bits;
+
+    /* the number of sectors we can read/write in this cycle */
+    sinfo->sectors_avail = s->sectors_per_block - block_offset;
+
+    sinfo->bytes_left = sinfo->sectors_avail << s->logical_sector_size_bits;
+
+    if (sinfo->sectors_avail > nb_sectors) {
+        sinfo->sectors_avail = nb_sectors;
+    }
+
+    sinfo->bytes_avail = sinfo->sectors_avail << s->logical_sector_size_bits;
+
+    sinfo->file_offset = s->bat[sinfo->bat_idx] >> VHDX_BAT_FILE_OFF_BITS;
+
+    sinfo->block_offset = block_offset << s->logical_sector_size_bits;
+
+    /* The file offset must be past the header section, so must be > 0 */
+    if (sinfo->file_offset == 0) {
+        return;
+    }
+
+    /* block offset is the offset in vhdx logical sectors, in
+     * the payload data block. Convert that to a byte offset
+     * in the block, and add in the payload data block offset
+     * in the file, in bytes, to get the final read address */
+
+    sinfo->file_offset <<= 20;  /* now in bytes, rather than 1MB units */
+    sinfo->file_offset += sinfo->block_offset;
+}
+
+
+
+static coroutine_fn int vhdx_co_readv(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    BDRVVHDXState *s = bs->opaque;
+    int ret = 0;
+    VHDXSectorInfo sinfo;
+    uint64_t bytes_done = 0;
+    QEMUIOVector hd_qiov;
+
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+
+    qemu_co_mutex_lock(&s->lock);
+
+    while (nb_sectors > 0) {
+        /* We are a differencing file, so we need to inspect the sector bitmap
+         * to see if we have the data or not */
+        if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
+            /* not supported yet */
+            ret = -ENOTSUP;
+            goto exit;
+        } else {
+            vhdx_block_translate(s, sector_num, nb_sectors, &sinfo);
+
+            qemu_iovec_reset(&hd_qiov);
+            qemu_iovec_concat(&hd_qiov, qiov,  bytes_done, sinfo.bytes_avail);
+
+            /* check the payload block state */
+            switch (s->bat[sinfo.bat_idx] & VHDX_BAT_STATE_BIT_MASK) {
+            case PAYLOAD_BLOCK_NOT_PRESENT: /* fall through */
+            case PAYLOAD_BLOCK_UNDEFINED:   /* fall through */
+            case PAYLOAD_BLOCK_UNMAPPED:    /* fall through */
+            case PAYLOAD_BLOCK_ZERO:
+                /* return zero */
+                qemu_iovec_memset(&hd_qiov, 0, 0, sinfo.bytes_avail);
+                break;
+            case PAYLOAD_BLOCK_FULL_PRESENT:
+                qemu_co_mutex_unlock(&s->lock);
+                ret = bdrv_co_readv(bs->file,
+                                    sinfo.file_offset >> BDRV_SECTOR_BITS,
+                                    sinfo.sectors_avail, &hd_qiov);
+                qemu_co_mutex_lock(&s->lock);
+                if (ret < 0) {
+                    goto exit;
+                }
+                break;
+            case PAYLOAD_BLOCK_PARTIALLY_PRESENT:
+                /* we don't yet support difference files, fall through
+                 * to error */
+            default:
+                ret = -EIO;
+                goto exit;
+                break;
+            }
+            nb_sectors -= sinfo.sectors_avail;
+            sector_num += sinfo.sectors_avail;
+            bytes_done += sinfo.bytes_avail;
+        }
+    }
+    ret = 0;
+exit:
+    qemu_co_mutex_unlock(&s->lock);
+    qemu_iovec_destroy(&hd_qiov);
+    return ret;
+}
+
+
+
+static coroutine_fn int vhdx_co_writev(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    return -ENOTSUP;
+}
+
+
+static void vhdx_close(BlockDriverState *bs)
+{
+    BDRVVHDXState *s = bs->opaque;
+    qemu_vfree(s->headers[0]);
+    qemu_vfree(s->headers[1]);
+    qemu_vfree(s->bat);
+    qemu_vfree(s->parent_entries);
+}
+
+static BlockDriver bdrv_vhdx = {
+    .format_name            = "vhdx",
+    .instance_size          = sizeof(BDRVVHDXState),
+    .bdrv_probe             = vhdx_probe,
+    .bdrv_open              = vhdx_open,
+    .bdrv_close             = vhdx_close,
+    .bdrv_reopen_prepare    = vhdx_reopen_prepare,
+    .bdrv_co_readv          = vhdx_co_readv,
+    .bdrv_co_writev         = vhdx_co_writev,
+};
+
+static void bdrv_vhdx_init(void)
+{
+    bdrv_register(&bdrv_vhdx);
+}
+
+block_init(bdrv_vhdx_init);
diff --git a/block/vhdx.h b/block/vhdx.h
new file mode 100644
index 000000000..c3b64c6ff
--- /dev/null
+++ b/block/vhdx.h
@@ -0,0 +1,325 @@
+/*
+ * Block driver for Hyper-V VHDX Images
+ *
+ * Copyright (c) 2013 Red Hat, Inc.,
+ *
+ * Authors:
+ *  Jeff Cody <jcody@redhat.com>
+ *
+ *  This is based on the "VHDX Format Specification v0.95", published 4/12/2012
+ *  by Microsoft:
+ *      https://www.microsoft.com/en-us/download/details.aspx?id=29681
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#ifndef BLOCK_VHDX_H
+#define BLOCK_VHDX_H
+
+/* Structures and fields present in the VHDX file */
+
+/* The header section has the following blocks,
+ * each block is 64KB:
+ *
+ * _____________________________________________________________________________
+ * | File Id. |   Header 1    | Header 2   | Region Table |  Reserved (768KB)  |
+ * |----------|---------------|------------|--------------|--------------------|
+ * |          |               |            |              |                    |
+ * 0.........64KB...........128KB........192KB..........256KB................1MB
+ */
+
+#define VHDX_HEADER_BLOCK_SIZE      (64*1024)
+
+#define VHDX_FILE_ID_OFFSET         0
+#define VHDX_HEADER1_OFFSET         (VHDX_HEADER_BLOCK_SIZE*1)
+#define VHDX_HEADER2_OFFSET         (VHDX_HEADER_BLOCK_SIZE*2)
+#define VHDX_REGION_TABLE_OFFSET    (VHDX_HEADER_BLOCK_SIZE*3)
+
+
+/*
+ * A note on the use of MS-GUID fields.  For more details on the GUID,
+ * please see: https://en.wikipedia.org/wiki/Globally_unique_identifier.
+ *
+ * The VHDX specification only states that these are MS GUIDs, and which
+ * bytes are data1-data4. It makes no mention of what algorithm should be used
+ * to generate the GUID, nor what standard.  However, looking at the specified
+ * known GUID fields, it appears the GUIDs are:
+ *  Standard/DCE GUID type  (noted by 10b in the MSB of byte 0 of .data4)
+ *  Random algorithm        (noted by 0x4XXX for .data3)
+ */
+
+/* ---- HEADER SECTION STRUCTURES ---- */
+
+/* These structures are ones that are defined in the VHDX specification
+ * document */
+
+typedef struct VHDXFileIdentifier {
+    uint64_t    signature;              /* "vhdxfile" in ASCII */
+    uint16_t    creator[256];           /* optional; utf-16 string to identify
+                                           the vhdx file creator.  Diagnotistic
+                                           only */
+} VHDXFileIdentifier;
+
+
+/* the guid is a 16 byte unique ID - the definition for this used by
+ * 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 {
+    uint32_t  data1;
+    uint16_t  data2;
+    uint16_t  data3;
+    uint8_t   data4[8];
+} MSGUID;
+
+#define guid_eq(a, b) \
+    (memcmp(&(a), &(b), sizeof(MSGUID)) == 0)
+
+#define VHDX_HEADER_SIZE (4*1024)   /* although the vhdx_header struct in disk
+                                       is only 582 bytes, for purposes of crc
+                                       the header is the first 4KB of the 64KB
+                                       block */
+
+/* The full header is 4KB, although the actual header data is much smaller.
+ * But for the checksum calculation, it is over the entire 4KB structure,
+ * not just the defined portion of it */
+typedef struct QEMU_PACKED VHDXHeader {
+    uint32_t    signature;              /* "head" in ASCII */
+    uint32_t    checksum;               /* CRC-32C hash of the whole header */
+    uint64_t    sequence_number;        /* Seq number of this header.  Each
+                                           VHDX file has 2 of these headers,
+                                           and only the header with the highest
+                                           sequence number is valid */
+    MSGUID      file_write_guid;       /* 128 bit unique identifier. Must be
+                                           updated to new, unique value before
+                                           the first modification is made to
+                                           file */
+    MSGUID      data_write_guid;        /* 128 bit unique identifier. Must be
+                                           updated to new, unique value before
+                                           the first modification is made to
+                                           visible data.   Visbile data is
+                                           defined as:
+                                                    - system & user metadata
+                                                    - raw block data
+                                                    - disk size
+                                                    - any change that will
+                                                      cause the virtual disk
+                                                      sector read to differ
+
+                                           This does not need to change if
+                                           blocks are re-arranged */
+    MSGUID      log_guid;               /* 128 bit unique identifier. If zero,
+                                           there is no valid log. If non-zero,
+                                           log entries with this guid are
+                                           valid. */
+    uint16_t    log_version;            /* version of the log format. Mustn't be
+                                           zero, unless log_guid is also zero */
+    uint16_t    version;                /* version of th evhdx file.  Currently,
+                                           only supported version is "1" */
+    uint32_t    log_length;             /* length of the log.  Must be multiple
+                                           of 1MB */
+    uint64_t    log_offset;             /* byte offset in the file of the log.
+                                           Must also be a multiple of 1MB */
+} VHDXHeader;
+
+/* Header for the region table block */
+typedef struct QEMU_PACKED VHDXRegionTableHeader {
+    uint32_t    signature;              /* "regi" in ASCII */
+    uint32_t    checksum;               /* CRC-32C hash of the 64KB table */
+    uint32_t    entry_count;            /* number of valid entries */
+    uint32_t    reserved;
+} VHDXRegionTableHeader;
+
+/* Individual region table entry.  There may be a maximum of 2047 of these
+ *
+ *  There are two known region table properties.  Both are required.
+ *  BAT (block allocation table):  2DC27766F62342009D64115E9BFD4A08
+ *  Metadata:                      8B7CA20647904B9AB8FE575F050F886E
+ */
+#define VHDX_REGION_ENTRY_REQUIRED  0x01    /* if set, parser must understand
+                                               this entry in order to open
+                                               file */
+typedef struct QEMU_PACKED VHDXRegionTableEntry {
+    MSGUID      guid;                   /* 128-bit unique identifier */
+    uint64_t    file_offset;            /* offset of the object in the file.
+                                           Must be multiple of 1MB */
+    uint32_t    length;                 /* length, in bytes, of the object */
+    uint32_t    data_bits;
+} VHDXRegionTableEntry;
+
+
+/* ---- LOG ENTRY STRUCTURES ---- */
+#define VHDX_LOG_HDR_SIZE 64
+typedef struct QEMU_PACKED VHDXLogEntryHeader {
+    uint32_t    signature;              /* "loge" in ASCII */
+    uint32_t    checksum;               /* CRC-32C hash of the 64KB table */
+    uint32_t    entry_length;           /* length in bytes, multiple of 1MB */
+    uint32_t    tail;                   /* byte offset of first log entry of a
+                                           seq, where this entry is the last
+                                           entry */
+    uint64_t    sequence_number;        /* incremented with each log entry.
+                                           May not be zero. */
+    uint32_t    descriptor_count;       /* number of descriptors in this log
+                                           entry, must be >= 0 */
+    uint32_t    reserved;
+    MSGUID      log_guid;               /* value of the log_guid from
+                                           vhdx_header.  If not found in
+                                           vhdx_header, it is invalid */
+    uint64_t    flushed_file_offset;    /* see spec for full details - this
+                                           sould be vhdx file size in bytes */
+    uint64_t    last_file_offset;       /* size in bytes that all allocated
+                                           file structures fit into */
+} VHDXLogEntryHeader;
+
+#define VHDX_LOG_DESC_SIZE 32
+
+typedef struct QEMU_PACKED VHDXLogDescriptor {
+    uint32_t    signature;              /* "zero" or "desc" in ASCII */
+    union  {
+        uint32_t    reserved;           /* zero desc */
+        uint32_t    trailing_bytes;     /* data desc: bytes 4092-4096 of the
+                                           data sector */
+    };
+    union {
+        uint64_t    zero_length;        /* zero desc: length of the section to
+                                           zero */
+        uint64_t    leading_bytes;      /* data desc: bytes 0-7 of the data
+                                           sector */
+    };
+    uint64_t    file_offset;            /* file offset to write zeros - multiple
+                                           of 4kB */
+    uint64_t    sequence_number;        /* must match same field in
+                                           vhdx_log_entry_header */
+} VHDXLogDescriptor;
+
+typedef struct QEMU_PACKED VHDXLogDataSector {
+    uint32_t    data_signature;         /* "data" in ASCII */
+    uint32_t    sequence_high;          /* 4 MSB of 8 byte sequence_number */
+    uint8_t     data[4084];             /* raw data, bytes 8-4091 (inclusive).
+                                           see the data descriptor field for the
+                                           other mising bytes */
+    uint32_t    sequence_low;           /* 4 LSB of 8 byte sequence_number */
+} VHDXLogDataSector;
+
+
+
+/* block states - different state values depending on whether it is a
+ * payload block, or a sector block. */
+
+#define PAYLOAD_BLOCK_NOT_PRESENT       0
+#define PAYLOAD_BLOCK_UNDEFINED         1
+#define PAYLOAD_BLOCK_ZERO              2
+#define PAYLOAD_BLOCK_UNMAPPED          5
+#define PAYLOAD_BLOCK_FULL_PRESENT      6
+#define PAYLOAD_BLOCK_PARTIALLY_PRESENT 7
+
+#define SB_BLOCK_NOT_PRESENT    0
+#define SB_BLOCK_PRESENT        6
+
+/* per the spec */
+#define VHDX_MAX_SECTORS_PER_BLOCK  (1<<23)
+
+/* upper 44 bits are the file offset in 1MB units lower 3 bits are the state
+   other bits are reserved */
+#define VHDX_BAT_STATE_BIT_MASK 0x07
+#define VHDX_BAT_FILE_OFF_BITS (64-44)
+typedef uint64_t VHDXBatEntry;
+
+/* ---- METADATA REGION STRUCTURES ---- */
+
+#define VHDX_METADATA_ENTRY_SIZE 32
+#define VHDX_METADATA_MAX_ENTRIES 2047  /* not including the header */
+#define VHDX_METADATA_TABLE_MAX_SIZE \
+    (VHDX_METADATA_ENTRY_SIZE * (VHDX_METADATA_MAX_ENTRIES+1))
+typedef struct QEMU_PACKED VHDXMetadataTableHeader {
+    uint64_t    signature;              /* "metadata" in ASCII */
+    uint16_t    reserved;
+    uint16_t    entry_count;            /* number table entries. <= 2047 */
+    uint32_t    reserved2[5];
+} VHDXMetadataTableHeader;
+
+#define VHDX_META_FLAGS_IS_USER         0x01    /* max 1024 entries */
+#define VHDX_META_FLAGS_IS_VIRTUAL_DISK 0x02    /* virtual disk metadata if set,
+                                                   otherwise file metdata */
+#define VHDX_META_FLAGS_IS_REQUIRED     0x04    /* parse must understand this
+                                                   entry to open the file */
+typedef struct QEMU_PACKED VHDXMetadataTableEntry {
+    MSGUID      item_id;                /* 128-bit identifier for metadata */
+    uint32_t    offset;                 /* byte offset of the metadata.  At
+                                           least 64kB.  Relative to start of
+                                           metadata region */
+                                        /* note: if length = 0, so is offset */
+    uint32_t    length;                 /* length of metadata. <= 1MB. */
+    uint32_t    data_bits;      /* least-significant 3 bits are flags, the
+                                   rest are reserved (see above) */
+    uint32_t    reserved2;
+} VHDXMetadataTableEntry;
+
+#define VHDX_PARAMS_LEAVE_BLOCKS_ALLOCED 0x01   /* Do not change any blocks to
+                                                   be BLOCK_NOT_PRESENT.
+                                                   If set indicates a fixed
+                                                   size VHDX file */
+#define VHDX_PARAMS_HAS_PARENT           0x02    /* has parent / backing file */
+typedef struct QEMU_PACKED VHDXFileParameters {
+    uint32_t    block_size;             /* size of each payload block, always
+                                           power of 2, <= 256MB and >= 1MB. */
+    uint32_t data_bits;     /* least-significant 2 bits are flags, the rest
+                               are reserved (see above) */
+} VHDXFileParameters;
+
+typedef struct QEMU_PACKED VHDXVirtualDiskSize {
+    uint64_t    virtual_disk_size;      /* Size of the virtual disk, in bytes.
+                                           Must be multiple of the sector size,
+                                           max of 64TB */
+} VHDXVirtualDiskSize;
+
+typedef struct QEMU_PACKED VHDXPage83Data {
+    MSGUID      page_83_data[16];       /* unique id for scsi devices that
+                                           support page 0x83 */
+} VHDXPage83Data;
+
+typedef struct QEMU_PACKED VHDXVirtualDiskLogicalSectorSize {
+    uint32_t    logical_sector_size;    /* virtual disk sector size (in bytes).
+                                           Can only be 512 or 4096 bytes */
+} VHDXVirtualDiskLogicalSectorSize;
+
+typedef struct QEMU_PACKED VHDXVirtualDiskPhysicalSectorSize {
+    uint32_t    physical_sector_size;   /* physical sector size (in bytes).
+                                           Can only be 512 or 4096 bytes */
+} VHDXVirtualDiskPhysicalSectorSize;
+
+typedef struct QEMU_PACKED VHDXParentLocatorHeader {
+    MSGUID      locator_type[16];       /* type of the parent virtual disk. */
+    uint16_t    reserved;
+    uint16_t    key_value_count;        /* number of key/value pairs for this
+                                           locator */
+} VHDXParentLocatorHeader;
+
+/* key and value strings are UNICODE strings, UTF-16 LE encoding, no NULs */
+typedef struct QEMU_PACKED VHDXParentLocatorEntry {
+    uint32_t    key_offset;             /* offset in metadata for key, > 0 */
+    uint32_t    value_offset;           /* offset in metadata for value, >0 */
+    uint16_t    key_length;             /* length of entry key, > 0 */
+    uint16_t    value_length;           /* length of entry value, > 0 */
+} VHDXParentLocatorEntry;
+
+
+/* ----- END VHDX SPECIFICATION STRUCTURES ---- */
+
+
+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)
+{
+    le32_to_cpus(&guid->data1);
+    le16_to_cpus(&guid->data2);
+    le16_to_cpus(&guid->data3);
+}
+
+#endif
diff --git a/block/vmdk.c b/block/vmdk.c
index 7bad757a3..608daaf93 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -32,11 +32,25 @@
 #define VMDK3_MAGIC (('C' << 24) | ('O' << 16) | ('W' << 8) | 'D')
 #define VMDK4_MAGIC (('K' << 24) | ('D' << 16) | ('M' << 8) | 'V')
 #define VMDK4_COMPRESSION_DEFLATE 1
+#define VMDK4_FLAG_NL_DETECT (1 << 0)
 #define VMDK4_FLAG_RGD (1 << 1)
+/* Zeroed-grain enable bit */
+#define VMDK4_FLAG_ZERO_GRAIN   (1 << 2)
 #define VMDK4_FLAG_COMPRESS (1 << 16)
 #define VMDK4_FLAG_MARKER (1 << 17)
 #define VMDK4_GD_AT_END 0xffffffffffffffffULL
 
+#define VMDK_GTE_ZEROED 0x1
+
+/* VMDK internal error codes */
+#define VMDK_OK      0
+#define VMDK_ERROR   (-1)
+/* Cluster not allocated */
+#define VMDK_UNALLOC (-2)
+#define VMDK_ZEROED  (-3)
+
+#define BLOCK_OPT_ZEROED_GRAIN "zeroed_grain"
+
 typedef struct {
     uint32_t version;
     uint32_t flags;
@@ -73,6 +87,8 @@ typedef struct VmdkExtent {
     bool flat;
     bool compressed;
     bool has_marker;
+    bool has_zero_grain;
+    int version;
     int64_t sectors;
     int64_t end_sector;
     int64_t flat_start_offset;
@@ -108,6 +124,7 @@ typedef struct VmdkMetaData {
     unsigned int l2_index;
     unsigned int l2_offset;
     int valid;
+    uint32_t *l2_cache_entry;
 } VmdkMetaData;
 
 typedef struct VmdkGrainMarker {
@@ -561,6 +578,8 @@ static int vmdk_open_vmdk4(BlockDriverState *bs,
     extent->compressed =
         le16_to_cpu(header.compressAlgorithm) == VMDK4_COMPRESSION_DEFLATE;
     extent->has_marker = le32_to_cpu(header.flags) & VMDK4_FLAG_MARKER;
+    extent->version = le32_to_cpu(header.version);
+    extent->has_zero_grain = le32_to_cpu(header.flags) & VMDK4_FLAG_ZERO_GRAIN;
     ret = vmdk_init_tables(bs, extent);
     if (ret) {
         /* free extent allocated by vmdk_add_extent */
@@ -578,22 +597,22 @@ static int vmdk_parse_description(const char *desc, const char *opt_name,
 
     opt_pos = strstr(desc, opt_name);
     if (!opt_pos) {
-        return -1;
+        return VMDK_ERROR;
     }
     /* Skip "=\"" following opt_name */
     opt_pos += strlen(opt_name) + 2;
     if (opt_pos >= end) {
-        return -1;
+        return VMDK_ERROR;
     }
     opt_end = opt_pos;
     while (opt_end < end && *opt_end != '"') {
         opt_end++;
     }
     if (opt_end == end || buf_size < opt_end - opt_pos + 1) {
-        return -1;
+        return VMDK_ERROR;
     }
     pstrcpy(buf, opt_end - opt_pos + 1, opt_pos);
-    return 0;
+    return VMDK_OK;
 }
 
 /* Open an extent file and append to bs array */
@@ -772,7 +791,7 @@ static int get_whole_cluster(BlockDriverState *bs,
         int ret;
 
         if (!vmdk_is_cid_valid(bs)) {
-            return -1;
+            return VMDK_ERROR;
         }
 
         /* floor offset to cluster */
@@ -780,30 +799,31 @@ static int get_whole_cluster(BlockDriverState *bs,
         ret = bdrv_read(bs->backing_hd, offset >> 9, whole_grain,
                 extent->cluster_sectors);
         if (ret < 0) {
-            return -1;
+            return VMDK_ERROR;
         }
 
         /* Write grain only into the active image */
         ret = bdrv_write(extent->file, cluster_offset, whole_grain,
                 extent->cluster_sectors);
         if (ret < 0) {
-            return -1;
+            return VMDK_ERROR;
         }
     }
-    return 0;
+    return VMDK_OK;
 }
 
 static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data)
 {
+    uint32_t offset;
+    QEMU_BUILD_BUG_ON(sizeof(offset) != sizeof(m_data->offset));
+    offset = cpu_to_le32(m_data->offset);
     /* update L2 table */
     if (bdrv_pwrite_sync(
                 extent->file,
                 ((int64_t)m_data->l2_offset * 512)
                     + (m_data->l2_index * sizeof(m_data->offset)),
-                &(m_data->offset),
-                sizeof(m_data->offset)
-            ) < 0) {
-        return -1;
+                &offset, sizeof(offset)) < 0) {
+        return VMDK_ERROR;
     }
     /* update backup L2 table */
     if (extent->l1_backup_table_offset != 0) {
@@ -812,13 +832,15 @@ static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data)
                     extent->file,
                     ((int64_t)m_data->l2_offset * 512)
                         + (m_data->l2_index * sizeof(m_data->offset)),
-                    &(m_data->offset), sizeof(m_data->offset)
-                ) < 0) {
-            return -1;
+                    &offset, sizeof(offset)) < 0) {
+            return VMDK_ERROR;
         }
     }
+    if (m_data->l2_cache_entry) {
+        *m_data->l2_cache_entry = offset;
+    }
 
-    return 0;
+    return VMDK_OK;
 }
 
 static int get_cluster_offset(BlockDriverState *bs,
@@ -830,24 +852,25 @@ static int get_cluster_offset(BlockDriverState *bs,
 {
     unsigned int l1_index, l2_offset, l2_index;
     int min_index, i, j;
-    uint32_t min_count, *l2_table, tmp = 0;
+    uint32_t min_count, *l2_table;
+    bool zeroed = false;
 
     if (m_data) {
         m_data->valid = 0;
     }
     if (extent->flat) {
         *cluster_offset = extent->flat_start_offset;
-        return 0;
+        return VMDK_OK;
     }
 
     offset -= (extent->end_sector - extent->sectors) * SECTOR_SIZE;
     l1_index = (offset >> 9) / extent->l1_entry_sectors;
     if (l1_index >= extent->l1_size) {
-        return -1;
+        return VMDK_ERROR;
     }
     l2_offset = extent->l1_table[l1_index];
     if (!l2_offset) {
-        return -1;
+        return VMDK_UNALLOC;
     }
     for (i = 0; i < L2_CACHE_SIZE; i++) {
         if (l2_offset == extent->l2_cache_offsets[i]) {
@@ -877,7 +900,7 @@ static int get_cluster_offset(BlockDriverState *bs,
                 l2_table,
                 extent->l2_size * sizeof(uint32_t)
             ) != extent->l2_size * sizeof(uint32_t)) {
-        return -1;
+        return VMDK_ERROR;
     }
 
     extent->l2_cache_offsets[min_index] = l2_offset;
@@ -886,9 +909,21 @@ static int get_cluster_offset(BlockDriverState *bs,
     l2_index = ((offset >> 9) / extent->cluster_sectors) % extent->l2_size;
     *cluster_offset = le32_to_cpu(l2_table[l2_index]);
 
-    if (!*cluster_offset) {
+    if (m_data) {
+        m_data->valid = 1;
+        m_data->l1_index = l1_index;
+        m_data->l2_index = l2_index;
+        m_data->offset = *cluster_offset;
+        m_data->l2_offset = l2_offset;
+        m_data->l2_cache_entry = &l2_table[l2_index];
+    }
+    if (extent->has_zero_grain && *cluster_offset == VMDK_GTE_ZEROED) {
+        zeroed = true;
+    }
+
+    if (!*cluster_offset || zeroed) {
         if (!allocate) {
-            return -1;
+            return zeroed ? VMDK_ZEROED : VMDK_UNALLOC;
         }
 
         /* Avoid the L2 tables update for the images that have snapshots. */
@@ -901,8 +936,7 @@ static int get_cluster_offset(BlockDriverState *bs,
         }
 
         *cluster_offset >>= 9;
-        tmp = cpu_to_le32(*cluster_offset);
-        l2_table[l2_index] = tmp;
+        l2_table[l2_index] = cpu_to_le32(*cluster_offset);
 
         /* First of all we write grain itself, to avoid race condition
          * that may to corrupt the image.
@@ -911,19 +945,15 @@ static int get_cluster_offset(BlockDriverState *bs,
          */
         if (get_whole_cluster(
                 bs, extent, *cluster_offset, offset, allocate) == -1) {
-            return -1;
+            return VMDK_ERROR;
         }
 
         if (m_data) {
-            m_data->offset = tmp;
-            m_data->l1_index = l1_index;
-            m_data->l2_index = l2_index;
-            m_data->l2_offset = l2_offset;
-            m_data->valid = 1;
+            m_data->offset = *cluster_offset;
         }
     }
     *cluster_offset <<= 9;
-    return 0;
+    return VMDK_OK;
 }
 
 static VmdkExtent *find_extent(BDRVVmdkState *s,
@@ -959,8 +989,8 @@ static int coroutine_fn vmdk_co_is_allocated(BlockDriverState *bs,
     ret = get_cluster_offset(bs, extent, NULL,
                             sector_num * 512, 0, &offset);
     qemu_co_mutex_unlock(&s->lock);
-    /* get_cluster_offset returning 0 means success */
-    ret = !ret;
+
+    ret = (ret == VMDK_OK || ret == VMDK_ZEROED);
 
     index_in_cluster = sector_num % extent->cluster_sectors;
     n = extent->cluster_sectors - index_in_cluster;
@@ -1103,9 +1133,9 @@ static int vmdk_read(BlockDriverState *bs, int64_t sector_num,
         if (n > nb_sectors) {
             n = nb_sectors;
         }
-        if (ret) {
+        if (ret != VMDK_OK) {
             /* if not allocated, try to read from parent image, if exist */
-            if (bs->backing_hd) {
+            if (bs->backing_hd && ret != VMDK_ZEROED) {
                 if (!vmdk_is_cid_valid(bs)) {
                     return -EINVAL;
                 }
@@ -1142,8 +1172,17 @@ static coroutine_fn int vmdk_co_read(BlockDriverState *bs, int64_t sector_num,
     return ret;
 }
 
+/**
+ * vmdk_write:
+ * @zeroed:       buf is ignored (data is zero), use zeroed_grain GTE feature
+ * if possible, otherwise return -ENOTSUP.
+ * @zero_dry_run: used for zeroed == true only, don't update L2 table, just
+ *
+ * Returns: error code with 0 for success.
+ */
 static int vmdk_write(BlockDriverState *bs, int64_t sector_num,
-                     const uint8_t *buf, int nb_sectors)
+                      const uint8_t *buf, int nb_sectors,
+                      bool zeroed, bool zero_dry_run)
 {
     BDRVVmdkState *s = bs->opaque;
     VmdkExtent *extent = NULL;
@@ -1173,7 +1212,7 @@ static int vmdk_write(BlockDriverState *bs, int64_t sector_num,
                                 sector_num << 9, !extent->compressed,
                                 &cluster_offset);
         if (extent->compressed) {
-            if (ret == 0) {
+            if (ret == VMDK_OK) {
                 /* Refuse write to allocated cluster for streamOptimized */
                 fprintf(stderr,
                         "VMDK: can't write to allocated cluster"
@@ -1189,7 +1228,7 @@ static int vmdk_write(BlockDriverState *bs, int64_t sector_num,
                                         &cluster_offset);
             }
         }
-        if (ret) {
+        if (ret == VMDK_ERROR) {
             return -EINVAL;
         }
         extent_begin_sector = extent->end_sector - extent->sectors;
@@ -1199,17 +1238,34 @@ static int vmdk_write(BlockDriverState *bs, int64_t sector_num,
         if (n > nb_sectors) {
             n = nb_sectors;
         }
-
-        ret = vmdk_write_extent(extent,
-                        cluster_offset, index_in_cluster * 512,
-                        buf, n, sector_num);
-        if (ret) {
-            return ret;
-        }
-        if (m_data.valid) {
-            /* update L2 tables */
-            if (vmdk_L2update(extent, &m_data) == -1) {
-                return -EIO;
+        if (zeroed) {
+            /* Do zeroed write, buf is ignored */
+            if (extent->has_zero_grain &&
+                    index_in_cluster == 0 &&
+                    n >= extent->cluster_sectors) {
+                n = extent->cluster_sectors;
+                if (!zero_dry_run) {
+                    m_data.offset = VMDK_GTE_ZEROED;
+                    /* update L2 tables */
+                    if (vmdk_L2update(extent, &m_data) != VMDK_OK) {
+                        return -EIO;
+                    }
+                }
+            } else {
+                return -ENOTSUP;
+            }
+        } else {
+            ret = vmdk_write_extent(extent,
+                            cluster_offset, index_in_cluster * 512,
+                            buf, n, sector_num);
+            if (ret) {
+                return ret;
+            }
+            if (m_data.valid) {
+                /* update L2 tables */
+                if (vmdk_L2update(extent, &m_data) != VMDK_OK) {
+                    return -EIO;
+                }
             }
         }
         nb_sectors -= n;
@@ -1235,14 +1291,29 @@ static coroutine_fn int vmdk_co_write(BlockDriverState *bs, int64_t sector_num,
     int ret;
     BDRVVmdkState *s = bs->opaque;
     qemu_co_mutex_lock(&s->lock);
-    ret = vmdk_write(bs, sector_num, buf, nb_sectors);
+    ret = vmdk_write(bs, sector_num, buf, nb_sectors, false, false);
+    qemu_co_mutex_unlock(&s->lock);
+    return ret;
+}
+
+static int coroutine_fn vmdk_co_write_zeroes(BlockDriverState *bs,
+                                             int64_t sector_num,
+                                             int nb_sectors)
+{
+    int ret;
+    BDRVVmdkState *s = bs->opaque;
+    qemu_co_mutex_lock(&s->lock);
+    ret = vmdk_write(bs, sector_num, NULL, nb_sectors, true, true);
+    if (!ret) {
+        ret = vmdk_write(bs, sector_num, NULL, nb_sectors, true, false);
+    }
     qemu_co_mutex_unlock(&s->lock);
     return ret;
 }
 
 
 static int vmdk_create_extent(const char *filename, int64_t filesize,
-                              bool flat, bool compress)
+                              bool flat, bool compress, bool zeroed_grain)
 {
     int ret, i;
     int fd = 0;
@@ -1264,9 +1335,10 @@ static int vmdk_create_extent(const char *filename, int64_t filesize,
     }
     magic = cpu_to_be32(VMDK4_MAGIC);
     memset(&header, 0, sizeof(header));
-    header.version = 1;
-    header.flags =
-        3 | (compress ? VMDK4_FLAG_COMPRESS | VMDK4_FLAG_MARKER : 0);
+    header.version = zeroed_grain ? 2 : 1;
+    header.flags = VMDK4_FLAG_RGD | VMDK4_FLAG_NL_DETECT
+                   | (compress ? VMDK4_FLAG_COMPRESS | VMDK4_FLAG_MARKER : 0)
+                   | (zeroed_grain ? VMDK4_FLAG_ZERO_GRAIN : 0);
     header.compressAlgorithm = compress ? VMDK4_COMPRESSION_DEFLATE : 0;
     header.capacity = filesize / 512;
     header.granularity = 128;
@@ -1357,7 +1429,7 @@ static int filename_decompose(const char *filename, char *path, char *prefix,
 
     if (filename == NULL || !strlen(filename)) {
         fprintf(stderr, "Vmdk: no filename provided.\n");
-        return -1;
+        return VMDK_ERROR;
     }
     p = strrchr(filename, '/');
     if (p == NULL) {
@@ -1369,7 +1441,7 @@ static int filename_decompose(const char *filename, char *path, char *prefix,
     if (p != NULL) {
         p++;
         if (p - filename >= buf_len) {
-            return -1;
+            return VMDK_ERROR;
         }
         pstrcpy(path, p - filename + 1, filename);
     } else {
@@ -1382,12 +1454,12 @@ static int filename_decompose(const char *filename, char *path, char *prefix,
         postfix[0] = '\0';
     } else {
         if (q - p >= buf_len) {
-            return -1;
+            return VMDK_ERROR;
         }
         pstrcpy(prefix, q - p + 1, p);
         pstrcpy(postfix, buf_len, q);
     }
-    return 0;
+    return VMDK_OK;
 }
 
 static int relative_path(char *dest, int dest_size,
@@ -1403,11 +1475,11 @@ static int relative_path(char *dest, int dest_size,
 #endif
 
     if (!(dest && base && target)) {
-        return -1;
+        return VMDK_ERROR;
     }
     if (path_is_absolute(target)) {
         pstrcpy(dest, dest_size, target);
-        return 0;
+        return VMDK_OK;
     }
     while (base[i] == target[i]) {
         i++;
@@ -1426,7 +1498,7 @@ static int relative_path(char *dest, int dest_size,
         pstrcat(dest, dest_size, sep);
     }
     pstrcat(dest, dest_size, q);
-    return 0;
+    return VMDK_OK;
 }
 
 static int vmdk_create(const char *filename, QEMUOptionParameter *options)
@@ -1447,6 +1519,7 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options)
     char parent_desc_line[BUF_SIZE] = "";
     uint32_t parent_cid = 0xffffffff;
     uint32_t number_heads = 16;
+    bool zeroed_grain = false;
     const char desc_template[] =
         "# Disk DescriptorFile\n"
         "version=1\n"
@@ -1482,6 +1555,8 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options)
             flags |= options->value.n ? BLOCK_FLAG_COMPAT6 : 0;
         } else if (!strcmp(options->name, BLOCK_OPT_SUBFMT)) {
             fmt = options->value.s;
+        } else if (!strcmp(options->name, BLOCK_OPT_ZEROED_GRAIN)) {
+            zeroed_grain |= options->value.n;
         }
         options++;
     }
@@ -1568,7 +1643,8 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options)
         snprintf(ext_filename, sizeof(ext_filename), "%s%s",
                 path, desc_filename);
 
-        if (vmdk_create_extent(ext_filename, size, flat, compress)) {
+        if (vmdk_create_extent(ext_filename, size,
+                               flat, compress, zeroed_grain)) {
             return -EINVAL;
         }
         filesize -= size;
@@ -1694,6 +1770,11 @@ static QEMUOptionParameter vmdk_create_options[] = {
             "VMDK flat extent format, can be one of "
             "{monolithicSparse (default) | monolithicFlat | twoGbMaxExtentSparse | twoGbMaxExtentFlat | streamOptimized} "
     },
+    {
+        .name = BLOCK_OPT_ZEROED_GRAIN,
+        .type = OPT_FLAG,
+        .help = "Enable efficient zero writes using the zeroed-grain GTE feature"
+    },
     { NULL }
 };
 
@@ -1705,6 +1786,7 @@ static BlockDriver bdrv_vmdk = {
     .bdrv_reopen_prepare = vmdk_reopen_prepare,
     .bdrv_read      = vmdk_co_read,
     .bdrv_write     = vmdk_co_write,
+    .bdrv_co_write_zeroes = vmdk_co_write_zeroes,
     .bdrv_close     = vmdk_close,
     .bdrv_create    = vmdk_create,
     .bdrv_co_flush_to_disk  = vmdk_co_flush,
diff --git a/blockdev.c b/blockdev.c
index 6e293e955..7c9d8dd0a 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1118,6 +1118,7 @@ int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
 void qmp_block_resize(const char *device, int64_t size, Error **errp)
 {
     BlockDriverState *bs;
+    int ret;
 
     bs = bdrv_find(device);
     if (!bs) {
@@ -1133,7 +1134,8 @@ void qmp_block_resize(const char *device, int64_t size, Error **errp)
     /* complete all in-flight operations before resizing the device */
     bdrv_drain_all();
 
-    switch (bdrv_truncate(bs, size)) {
+    ret = bdrv_truncate(bs, size);
+    switch (ret) {
     case 0:
         break;
     case -ENOMEDIUM:
@@ -1149,7 +1151,7 @@ void qmp_block_resize(const char *device, int64_t size, Error **errp)
         error_set(errp, QERR_DEVICE_IN_USE, device);
         break;
     default:
-        error_set(errp, QERR_UNDEFINED_ERROR);
+        error_setg_errno(errp, -ret, "Could not resize");
         break;
     }
 }
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 0903d7a60..c90f5e4d9 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -58,7 +58,8 @@ enum {
 
 #define NBD_DEFAULT_PORT	10809
 
-#define NBD_BUFFER_SIZE (1024*1024)
+/* Maximum size of a single READ/WRITE data buffer */
+#define NBD_MAX_BUFFER_SIZE (32 * 1024 * 1024)
 
 ssize_t nbd_wr_sync(int fd, void *buffer, size_t size, bool do_read);
 int tcp_socket_incoming(const char *address, uint16_t port);
diff --git a/include/qemu/crc32c.h b/include/qemu/crc32c.h
new file mode 100644
index 000000000..56d1c3bfd
--- /dev/null
+++ b/include/qemu/crc32c.h
@@ -0,0 +1,35 @@
+/*
+ *  Castagnoli CRC32C Checksum Algorithm
+ *
+ *  Polynomial: 0x11EDC6F41
+ *
+ *  Castagnoli93: Guy Castagnoli and Stefan Braeuer and Martin Herrman
+ *               "Optimization of Cyclic Redundancy-Check Codes with 24
+ *                 and 32 Parity Bits",IEEE Transactions on Communication,
+ *                Volume 41, Number 6, June 1993
+ *
+ *  Copyright (c) 2013 Red Hat, Inc.,
+ *
+ *  Authors:
+ *   Jeff Cody <jcody@redhat.com>
+ *
+ *  Based on the Linux kernel cryptographic crc32c module,
+ *
+ *  Copyright (c) 2004 Cisco Systems, Inc.
+ *  Copyright (c) 2008 Herbert Xu <herbert@gondor.apana.org.au>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ */
+
+#ifndef QEMU_CRC32_H
+#define QEMU_CRC32_H
+
+#include "qemu-common.h"
+
+uint32_t crc32c(uint32_t crc, const uint8_t *data, unsigned int length);
+
+#endif
diff --git a/nbd.c b/nbd.c
index 85187fff9..2606403a4 100644
--- a/nbd.c
+++ b/nbd.c
@@ -98,7 +98,6 @@ struct NBDExport {
     off_t size;
     uint32_t nbdflags;
     QTAILQ_HEAD(, NBDClient) clients;
-    QSIMPLEQ_HEAD(, NBDRequest) requests;
     QTAILQ_ENTRY(NBDExport) next;
 };
 
@@ -845,18 +844,11 @@ void nbd_client_close(NBDClient *client)
 static NBDRequest *nbd_request_get(NBDClient *client)
 {
     NBDRequest *req;
-    NBDExport *exp = client->exp;
 
     assert(client->nb_requests <= MAX_NBD_REQUESTS - 1);
     client->nb_requests++;
 
-    if (QSIMPLEQ_EMPTY(&exp->requests)) {
-        req = g_malloc0(sizeof(NBDRequest));
-        req->data = qemu_blockalign(exp->bs, NBD_BUFFER_SIZE);
-    } else {
-        req = QSIMPLEQ_FIRST(&exp->requests);
-        QSIMPLEQ_REMOVE_HEAD(&exp->requests, entry);
-    }
+    req = g_slice_new0(NBDRequest);
     nbd_client_get(client);
     req->client = client;
     return req;
@@ -865,7 +857,12 @@ static NBDRequest *nbd_request_get(NBDClient *client)
 static void nbd_request_put(NBDRequest *req)
 {
     NBDClient *client = req->client;
-    QSIMPLEQ_INSERT_HEAD(&client->exp->requests, req, entry);
+
+    if (req->data) {
+        qemu_vfree(req->data);
+    }
+    g_slice_free(NBDRequest, req);
+
     if (client->nb_requests-- == MAX_NBD_REQUESTS) {
         qemu_notify_event();
     }
@@ -877,7 +874,6 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset,
                           void (*close)(NBDExport *))
 {
     NBDExport *exp = g_malloc0(sizeof(NBDExport));
-    QSIMPLEQ_INIT(&exp->requests);
     exp->refcount = 1;
     QTAILQ_INIT(&exp->clients);
     exp->bs = bs;
@@ -953,13 +949,6 @@ void nbd_export_put(NBDExport *exp)
             exp->close(exp);
         }
 
-        while (!QSIMPLEQ_EMPTY(&exp->requests)) {
-            NBDRequest *first = QSIMPLEQ_FIRST(&exp->requests);
-            QSIMPLEQ_REMOVE_HEAD(&exp->requests, entry);
-            qemu_vfree(first->data);
-            g_free(first);
-        }
-
         g_free(exp);
     }
 }
@@ -1018,6 +1007,7 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
 {
     NBDClient *client = req->client;
     int csock = client->sock;
+    uint32_t command;
     ssize_t rc;
 
     client->recv_coroutine = qemu_coroutine_self();
@@ -1029,9 +1019,9 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
         goto out;
     }
 
-    if (request->len > NBD_BUFFER_SIZE) {
+    if (request->len > NBD_MAX_BUFFER_SIZE) {
         LOG("len (%u) is larger than max len (%u)",
-            request->len, NBD_BUFFER_SIZE);
+            request->len, NBD_MAX_BUFFER_SIZE);
         rc = -EINVAL;
         goto out;
     }
@@ -1045,7 +1035,11 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
 
     TRACE("Decoding type");
 
-    if ((request->type & NBD_CMD_MASK_COMMAND) == NBD_CMD_WRITE) {
+    command = request->type & NBD_CMD_MASK_COMMAND;
+    if (command == NBD_CMD_READ || command == NBD_CMD_WRITE) {
+        req->data = qemu_blockalign(client->exp->bs, request->len);
+    }
+    if (command == NBD_CMD_WRITE) {
         TRACE("Reading %u byte(s)", request->len);
 
         if (qemu_co_recv(csock, req->data, request->len) != request->len) {
diff --git a/tests/qemu-iotests/common.rc b/tests/qemu-iotests/common.rc
index a536bf70a..31eb62b60 100644
--- a/tests/qemu-iotests/common.rc
+++ b/tests/qemu-iotests/common.rc
@@ -127,6 +127,9 @@ _make_test_img()
             -e "s# compat='[^']*'##g" \
             -e "s# compat6=\\(on\\|off\\)##g" \
             -e "s# static=\\(on\\|off\\)##g" \
+            -e "s# zeroed_grain=\\(on\\|off\\)##g" \
+            -e "s# subformat='[^']*'##g" \
+            -e "s# adapter_type='[^']*'##g" \
             -e "s# lazy_refcounts=\\(on\\|off\\)##g"
 
     # Start an NBD server on the image file, which is what we'll be talking to
diff --git a/util/Makefile.objs b/util/Makefile.objs
index c5652f526..4a1bd4ee3 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -10,3 +10,4 @@ util-obj-$(CONFIG_POSIX) += compatfd.o
 util-obj-y += iov.o aes.o qemu-config.o qemu-sockets.o uri.o notify.o
 util-obj-y += qemu-option.o qemu-progress.o
 util-obj-y += hexdump.o
+util-obj-y += crc32c.o
diff --git a/util/crc32c.c b/util/crc32c.c
new file mode 100644
index 000000000..886632780
--- /dev/null
+++ b/util/crc32c.c
@@ -0,0 +1,115 @@
+/*
+ *  Castagnoli CRC32C Checksum Algorithm
+ *
+ *  Polynomial: 0x11EDC6F41
+ *
+ *  Castagnoli93: Guy Castagnoli and Stefan Braeuer and Martin Herrman
+ *               "Optimization of Cyclic Redundancy-Check Codes with 24
+ *                 and 32 Parity Bits",IEEE Transactions on Communication,
+ *                Volume 41, Number 6, June 1993
+ *
+ *  Copyright (c) 2013 Red Hat, Inc.,
+ *
+ *  Authors:
+ *   Jeff Cody <jcody@redhat.com>
+ *
+ *  Based on the Linux kernel cryptographic crc32c module,
+ *
+ *  Copyright (c) 2004 Cisco Systems, Inc.
+ *  Copyright (c) 2008 Herbert Xu <herbert@gondor.apana.org.au>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ */
+
+#include "qemu-common.h"
+#include "qemu/crc32c.h"
+
+/*
+ * This is the CRC-32C table
+ * Generated with:
+ * width = 32 bits
+ * poly = 0x1EDC6F41
+ * reflect input bytes = true
+ * reflect output bytes = true
+ */
+
+static const uint32_t crc32c_table[256] = {
+    0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
+    0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
+    0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
+    0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
+    0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
+    0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
+    0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
+    0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
+    0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
+    0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
+    0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
+    0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
+    0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
+    0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
+    0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
+    0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
+    0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
+    0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
+    0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
+    0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
+    0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
+    0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
+    0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
+    0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
+    0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
+    0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
+    0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
+    0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
+    0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
+    0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
+    0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
+    0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
+    0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
+    0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
+    0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
+    0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
+    0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
+    0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
+    0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
+    0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
+    0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
+    0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
+    0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
+    0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
+    0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
+    0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
+    0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
+    0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
+    0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
+    0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
+    0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
+    0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
+    0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
+    0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
+    0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
+    0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
+    0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
+    0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
+    0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
+    0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
+    0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
+    0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
+    0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
+    0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L
+};
+
+
+uint32_t crc32c(uint32_t crc, const uint8_t *data, unsigned int length)
+{
+    while (length--) {
+        crc = crc32c_table[(crc ^ *data++) & 0xFFL] ^ (crc >> 8);
+    }
+    return crc^0xffffffff;
+}
+