Commit 14ead646 authored by Fam Zheng's avatar Fam Zheng Committed by Stefan Hajnoczi
Browse files

vmdk: add support for “zeroed‐grain” GTE 

Introduced support for zeroed-grain GTE, as specified in Virtual Disk
Format 5.0[1].

    Recent VMware hosted platform products support a new “zeroed‐grain”
    grain table entry (GTE). The zeroed‐grain GTE returns all zeros on
    read.  In other words, the zeroed‐grain GTE indicates that a grain
    in the child disk is zero‐filled but does not actually occupy space
    in storage.  A sparse extent with zeroed‐grain GTE has the following
    in its header:

     * SparseExtentHeader.version = 2
     * SparseExtentHeader.flags has bit 2 set

    Other than the new flag and the possibly zeroed‐grain GTE, version 2
    sparse extents are identical to version 1.  Also, a zeroed‐grain GTE
    has value 0x1 in the GT table.

[1] Virtual Disk Format 5.0, http://www.vmware.com/support/developer/vddk/vmdk_50_technote.pdf?src=vmdk


Signed-off-by: default avatarFam Zheng <famz@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 65f74725

block/vmdk.c

+18 −6
Original line number Diff line number Diff line
@@ -33,10 +33,13 @@ 
#define VMDK4_MAGIC (('K' << 24) | ('D' << 16) | ('M' << 8) | 'V')

#define VMDK4_COMPRESSION_DEFLATE 1

#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
@@ -81,6 +84,8 @@ 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;
@@ -569,6 +574,8 @@ 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 */
@@ -839,6 +846,7 @@ 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;

    bool zeroed = false;



    if (m_data) {

        m_data->valid = 0;
@@ -894,9 +902,13 @@ 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 (extent->has_zero_grain && *cluster_offset == VMDK_GTE_ZEROED) {

        zeroed = true;

    }



    if (!*cluster_offset || zeroed) {

        if (!allocate) {

            return VMDK_UNALLOC;

            return zeroed ? VMDK_ZEROED : VMDK_UNALLOC;

        }



        /* Avoid the L2 tables update for the images that have snapshots. */
@@ -967,8 +979,8 @@ 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;
@@ -1111,9 +1123,9 @@ 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;

                }