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Re: [Qemu-devel] [PATCH RESEND] Support vhd type VHD_DIFFERENCING
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From: |
Xiaodong Gong |
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Subject: |
Re: [Qemu-devel] [PATCH RESEND] Support vhd type VHD_DIFFERENCING |
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Date: |
Tue, 14 Oct 2014 21:32:11 +0800 |
>Adjusting coding style can be made into a separate patch in vpc.c file.
>Such as using '{}' at if conditional statement.
I'll revert this.
>Please use g_malloc0() instead of malloc and memset(,0,).
This api is great, I'll use it.
>A bug, right?
yes, really a bug, thx a lot.
>in your patch, if error happened, not only -1 is returned, you have to describe
>the reason clearer IMO.
-1 is error, -2 is sector not allocated, -3 is allocated in backing
file.described
before get_sector_offset. and what's the meaning of IMO ? :)
On 10/11/14, Gonglei <address@hidden> wrote:
> On 2014/10/11 0:17, Xiaodong Gong wrote:
>
>> Now qemu only supports vhd type VHD_FIXED and VHD_DYNAMIC, so qemu
>> can't read snapshot volume of vhd, and can't support other storage
>> features of vhd file.
>>
>> This patch add read parent information in function "vpc_open", read
>> bitmap in "vpc_read", and change bitmap in "vpc_write".
>>
>> Signed-off-by: Xiaodong Gong <address@hidden>
>> ---
>> Changes since v4:
>> - Parse the batmap only when the version of VHD > 1.2.
>> - Add support to parent location of W2RU.
>>
>> Changes since v3:
>> - Remove the PARENT_MAX_LOC.
>>
>> Changes since v2:
>> - Change MACX to PLATFAORM_MACX.
>> - Return with EINVAL to parent location is W2RU and W2KU.
>> - Change -1 == ret to a natrual order of ret == -1.
>> - Get rid of the get_sector_offset_diff, get_sector_offset
>> supports VHD_DIFF.
>> - Return code of get_sector_offset is set to, -1 for error,
>> -2 for not allocate, -3 for in parent.
>> - Fix un init ret of vpc_write, when nb_sector == 0.
>> - Change if (diff == ture) to if (diff) and so on.
>> - Add PARENT_MAX_LOC to more understand.
>> - Restore the boundary check to write on dynamic type in
>> get_sector_offset.
>>
>> Changes since v1:
>> - Add Boundary check to any input.
>> - Clean the code no used after in vpc_open.
>> - Change bdrv_co_readv() to bdrv_preadv in vpc_read.
>> - Added some code to make it easy to understand.
>> ---
>> block/vpc.c | 428
>> ++++++++++++++++++++++++++++++++++++++++++++++++++----------
>> 1 file changed, 357 insertions(+), 71 deletions(-)
>>
>> diff --git a/block/vpc.c b/block/vpc.c
>> index 4947369..1210542 100644
>> --- a/block/vpc.c
>> +++ b/block/vpc.c
>> @@ -29,17 +29,27 @@
>> #if defined(CONFIG_UUID)
>> #include <uuid/uuid.h>
>> #endif
>> +#include <iconv.h>
>>
>> /**************************************************************/
>>
>> #define HEADER_SIZE 512
>> +#define DYNAMIC_HEADER_SIZE 1024
>> +#define PARENT_LOCATOR_NUM 8
>> +#define MACX_PREFIX_LEN 7 /* file:// */
>> +#define TBBATMAP_HEAD_SIZE 28
>> +
>> +#define PLATFORM_MACX 0x5863614d /* big endian */
>> +#define PLATFORM_W2RU 0x75723257
>> +
>> +#define VHD_VERSION(major, minor) (((major) << 16) | ((minor) &
>> 0x0000FFFF))
>>
>> //#define CACHE
>>
>> enum vhd_type {
>> VHD_FIXED = 2,
>> VHD_DYNAMIC = 3,
>> - VHD_DIFFERENCING = 4,
>> + VHD_DIFF = 4,
>> };
>>
>> // Seconds since Jan 1, 2000 0:00:00 (UTC)
>> @@ -138,6 +148,15 @@ typedef struct BDRVVPCState {
>> Error *migration_blocker;
>> } BDRVVPCState;
>>
>> +typedef struct vhd_tdbatmap_header {
>> + char magic[8]; /* always "tdbatmap" */
>> +
>> + uint64_t batmap_offset;
>> + uint32_t batmap_size;
>> + uint32_t batmap_version;
>> + uint32_t checksum;
>> +} QEMU_PACKED VHDTdBatmapHeader;
>> +
>> static uint32_t vpc_checksum(uint8_t* buf, size_t size)
>> {
>> uint32_t res = 0;
>> @@ -153,10 +172,107 @@ static uint32_t vpc_checksum(uint8_t* buf, size_t
>> size)
>> static int vpc_probe(const uint8_t *buf, int buf_size, const char
>> *filename)
>> {
>> if (buf_size >= 8 && !strncmp((char *)buf, "conectix", 8))
>> - return 100;
>> + return 100;
>
>
> Adjusting coding style can be made into a separate patch in vpc.c file.
> Such as using '{}' at if conditional statement.
>
>> return 0;
>> }
>>
>> +static int vpc_read_backing_loc(VHDDynDiskHeader *dyndisk_header,
>> + BlockDriverState *bs,
>> + Error **errp)
>> +{
>> + BDRVVPCState *s = bs->opaque;
>> + int64_t data_offset = 0;
>> + int data_length = 0;
>> + uint32_t platform;
>> + bool done = false;
>> + int parent_locator_offset = 0;
>> + int i;
>> + int ret = 0;
>> +
>> + for (i = 0; i < PARENT_LOCATOR_NUM; i++) {
>> + data_offset =
>> + be64_to_cpu(dyndisk_header->parent_locator[i].data_offset);
>> + data_length =
>> + be32_to_cpu(dyndisk_header->parent_locator[i].data_length);
>> + platform = dyndisk_header->parent_locator[i].platform;
>> +
>> + /* Extend the location offset */
>> + if (parent_locator_offset < data_offset) {
>> + parent_locator_offset = data_offset;
>> + }
>> +
>> + if (done) {
>> + continue;
>> + }
>> +
>> + /* Skip "file://" in MacX platform */
>> + if (platform == PLATFORM_MACX) {
>> + data_offset += MACX_PREFIX_LEN;
>> + data_length -= MACX_PREFIX_LEN;
>> + }
>> +
>> + /* Read location of backing file */
>> + if (platform == PLATFORM_MACX || platform == PLATFORM_W2RU) {
>> + if (data_offset > s->max_table_entries * s->block_size) {
>> + return -1;
>> + }
>> + if (data_length > BDRV_SECTOR_SIZE) {
>> + return -1;
>> + }
>> + ret = bdrv_pread(bs->file, data_offset, bs->backing_file,
>> + data_length);
>> + if (ret < 0) {
>> + return ret;
>> + }
>> + bs->backing_file[data_length] = '\0';
>> + }
>> +
>> + /* Convert location to ACSII string */
>> + if (platform == PLATFORM_MACX) {
>> + done = true;
>> +
>> + } else if (platform == PLATFORM_W2RU) {
>> + /* Must be UTF16-LE to ASCII */
>> + char *out, *optr;
>> + int j;
>> +
>> + optr = out = (char *) malloc(data_length + 1);
>> + if (out == NULL) {
>> + ret = -1;
>> + return ret;
>> + }
>> + memset(out, 0, data_length + 1);
>
>
> Please use g_malloc0() instead of malloc and memset(,0,).
>
>> +
>> + for (j = 0; j < data_length + 1; j++) {
>> + out[j] = bs->backing_file[2*j];
>> + }
>> + out[data_length + 1] = '\0';
>> +
>> + while (*optr != '\0') {
>> + if (*optr == '\\') {
>> + *optr = '/';
>> + }
>> + optr++;
>> + }
>> +
>> + strncpy(bs->backing_file, out, data_length + 1);
>> +
>> + out = NULL;
>> + free(out);
>
>
> A bug, right?
>
>> +
>> + done = true;
>> + }
>> + }
>> +
>> + if (bs->backing_file[0] == '\0') {
>> + error_setg(errp, "block-vpc: differencing is not support in
>> w2ku");
>> + ret = -EINVAL;
>> + return ret;
>> + }
>> +
>> + return parent_locator_offset;
>> +}
>> +
>> static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
>> Error **errp)
>> {
>> @@ -164,11 +280,14 @@ static int vpc_open(BlockDriverState *bs, QDict
>> *options, int flags,
>> int i;
>> VHDFooter *footer;
>> VHDDynDiskHeader *dyndisk_header;
>> - uint8_t buf[HEADER_SIZE];
>> + uint8_t buf[DYNAMIC_HEADER_SIZE];
>> + uint8_t tdbatmap_header_buf[TBBATMAP_HEAD_SIZE];
>> uint32_t checksum;
>> uint64_t computed_size;
>> - int disk_type = VHD_DYNAMIC;
>> + uint32_t disk_type;
>> int ret;
>> + VHDTdBatmapHeader *tdbatmap_header;
>> + int parent_locator_offset = 0;
>>
>> ret = bdrv_pread(bs->file, 0, s->footer_buf, HEADER_SIZE);
>> if (ret < 0) {
>> @@ -176,6 +295,8 @@ static int vpc_open(BlockDriverState *bs, QDict
>> *options, int flags,
>> }
>>
>> footer = (VHDFooter *) s->footer_buf;
>> + disk_type = be32_to_cpu(footer->type);
>> +
>> if (strncmp(footer->creator, "conectix", 8)) {
>> int64_t offset = bdrv_getlength(bs->file);
>> if (offset < 0) {
>> @@ -230,9 +351,9 @@ static int vpc_open(BlockDriverState *bs, QDict
>> *options, int flags,
>> goto fail;
>> }
>>
>> - if (disk_type == VHD_DYNAMIC) {
>> + if (disk_type == VHD_DYNAMIC || disk_type == VHD_DIFF) {
>> ret = bdrv_pread(bs->file, be64_to_cpu(footer->data_offset),
>> buf,
>> - HEADER_SIZE);
>> + DYNAMIC_HEADER_SIZE);
>> if (ret < 0) {
>> goto fail;
>> }
>> @@ -286,6 +407,37 @@ static int vpc_open(BlockDriverState *bs, QDict
>> *options, int flags,
>> s->free_data_block_offset =
>> (s->bat_offset + (s->max_table_entries * 4) + 511) & ~511;
>>
>> + /* Read tdbatmap header by offset */
>> + if (footer->version >= VHD_VERSION(1, 2)) {
>> + ret = bdrv_pread(bs->file, s->free_data_block_offset,
>> + tdbatmap_header_buf, TBBATMAP_HEAD_SIZE);
>> + if (ret < 0) {
>> + goto fail;
>> + }
>> +
>> + tdbatmap_header = (VHDTdBatmapHeader *) tdbatmap_header_buf;
>> + if (!strncmp(tdbatmap_header->magic, "tdbatmap", 8)) {
>> + s->free_data_block_offset =
>> + be32_to_cpu(tdbatmap_header->batmap_size) * 512
>> + + be64_to_cpu(tdbatmap_header->batmap_offset);
>> + }
>> + }
>> +
>> + /* Read backing file location from dyn header table */
>> + if (dyndisk_header->parent_name[0] ||
>> dyndisk_header->parent_name[1]) {
>> + ret = parent_locator_offset =
>> vpc_read_backing_loc(dyndisk_header,
>> + bs, errp);
>> + if (ret < 0) {
>> + goto fail;
>> + }
>> + }
>> +
>> + if (s->free_data_block_offset < parent_locator_offset
>> + + BDRV_SECTOR_SIZE) {
>> + s->free_data_block_offset = parent_locator_offset
>> + + BDRV_SECTOR_SIZE;
>> + }
>> +
>> for (i = 0; i < s->max_table_entries; i++) {
>> be32_to_cpus(&s->pagetable[i]);
>> if (s->pagetable[i] != 0xFFFFFFFF) {
>> @@ -340,35 +492,76 @@ static int vpc_reopen_prepare(BDRVReopenState
>> *state,
>> }
>>
>> /*
>> - * Returns the absolute byte offset of the given sector in the image
>> file.
>> - * If the sector is not allocated, -1 is returned instead.
>> + * Returns the absolute byte offset of the given sector in the
>> differencing
>> + * image file.
>> + *
>> + * If error happened, -1 is returned.
>
>
> In your patch, if error happened, not only -1 is returned, you have to
> describe
> the reason clearer IMO.
>
>> + *
>> + * When write all type or read dynamic, if the sector is not allocated,
>> -2
>> + * is returned instead. If the sector is allocated in current file, the
>> block
>> + * offset is returned.
>> *
>> - * The parameter write must be 1 if the offset will be used for a write
>> - * operation (the block bitmaps is updated then), 0 otherwise.
>> + * When read diff. If the sector is not allocated, -2 is returned
>> instead.
>> + * If the sector is allocated in the backing file, -3 is returned. If
>> the
>> + * sector is allocated in current file, the block offset is returned.
>> */
>> static inline int64_t get_sector_offset(BlockDriverState *bs,
>> - int64_t sector_num, int write)
>> + int64_t sector_num, bool write, bool diff)
>> {
>> BDRVVPCState *s = bs->opaque;
>> - uint64_t offset = sector_num * 512;
>> - uint64_t bitmap_offset, block_offset;
>> + uint64_t offset = sector_num << BDRV_SECTOR_BITS;
>> + uint64_t bitmap_offset;
>> uint32_t pagetable_index, pageentry_index;
>> + int64_t block_offset = LONG_MIN;
>> + int ret;
>>
>> pagetable_index = offset / s->block_size;
>> - pageentry_index = (offset % s->block_size) / 512;
>> + pageentry_index = (offset % s->block_size) >> BDRV_SECTOR_BITS;
>>
>> - if (pagetable_index >= s->max_table_entries ||
>> s->pagetable[pagetable_index] == 0xffffffff)
>> - return -1; // not allocated
>> + if (pagetable_index >= s->max_table_entries) {
>> + return -2;
>> + }
>> + if (s->pagetable[pagetable_index] == 0xffffffff) {
>> + if (!write && diff) {
>> + return -3; /* parent allocated */
>> + } else {
>> + return -2; /* not allocated */
>> + }
>> + }
>>
>> - bitmap_offset = 512 * (uint64_t) s->pagetable[pagetable_index];
>> - block_offset = bitmap_offset + s->bitmap_size + (512 *
>> pageentry_index);
>> + bitmap_offset = (uint64_t) s->pagetable[pagetable_index]
>> + << BDRV_SECTOR_BITS;
>> +
>> + if (!diff || write) {
>> + block_offset = bitmap_offset + s->bitmap_size
>> + + (pageentry_index << BDRV_SECTOR_BITS);
>> + } else {
>> + uint32_t bitmap_index, bitmapentry_index;
>> + uint8_t bitmap[s->bitmap_size];
>>
>> + if (bitmap_offset > s->max_table_entries * s->block_size) {
>> + return -1;
>> + }
>> + ret = bdrv_pread(bs->file, bitmap_offset, bitmap,
>> s->bitmap_size);
>> + if (ret < 0) {
>> + return -1;
>> + }
>> +
>> + bitmap_index = pageentry_index / 8;
>> + bitmapentry_index = 7 - pageentry_index % 8;
>> + if (bitmap[bitmap_index] & 0x1 << bitmapentry_index) {
>> + block_offset = bitmap_offset + s->bitmap_size
>> + + (pageentry_index << BDRV_SECTOR_BITS);
>> + } else {
>> + return -3;
>> + }
>> + }
>> // We must ensure that we don't write to any sectors which are marked
>> as
>> // unused in the bitmap. We get away with setting all bits in the
>> block
>> // bitmap each time we write to a new block. This might cause Virtual
>> PC to
>> // miss sparse read optimization, but it's not a problem in terms of
>> // correctness.
>> - if (write && (s->last_bitmap_offset != bitmap_offset)) {
>> + if (!diff && write && (s->last_bitmap_offset != bitmap_offset)) {
>> uint8_t bitmap[s->bitmap_size];
>>
>> s->last_bitmap_offset = bitmap_offset;
>> @@ -376,7 +569,7 @@ static inline int64_t
>> get_sector_offset(BlockDriverState *bs,
>> bdrv_pwrite_sync(bs->file, bitmap_offset, bitmap,
>> s->bitmap_size);
>> }
>>
>> -// printf("sector: %" PRIx64 ", index: %x, offset: %x, bioff: %"
>> PRIx64 ", bloff: %" PRIx64 "\n",
>> +// printf("sector: %" PRIx64 ", index: %x, offset: %x, bioff: %" PRIx64
>> ", bloff: %" PRIx64 "\n",
>
>
> WARNING: line over 80 characters
> #369: FILE: block/vpc.c:572:
> +// printf("sector: %" PRIx64 ", index: %x, offset: %x, bioff: %" PRIx64 ",
> bloff: %" PRIx64 "\n",
>
> ERROR: do not use C99 // comments
> #369: FILE: block/vpc.c:572:
> +// printf("sector: %" PRIx64 ", index: %x, offset: %x, bioff: %" PRIx64 ",
> bloff: %" PRIx64 "\n",
>
> total: 1 errors, 1 warnings, 571 lines checked
>
>> // sector_num, pagetable_index, pageentry_index,
>> // bitmap_offset, block_offset);
>>
>> @@ -437,7 +630,8 @@ static int rewrite_footer(BlockDriverState* bs)
>> *
>> * Returns the sectors' offset in the image file on success and < 0 on
>> error
>> */
>> -static int64_t alloc_block(BlockDriverState* bs, int64_t sector_num)
>> +static int64_t alloc_block(BlockDriverState *bs, int64_t sector_num,
>> + bool diff)
>> {
>> BDRVVPCState *s = bs->opaque;
>> int64_t bat_offset;
>> @@ -457,7 +651,11 @@ static int64_t alloc_block(BlockDriverState* bs,
>> int64_t sector_num)
>> s->pagetable[index] = s->free_data_block_offset / 512;
>>
>> // Initialize the block's bitmap
>> - memset(bitmap, 0xff, s->bitmap_size);
>> + if (diff) {
>> + memset(bitmap, 0x0, s->bitmap_size);
>> + } else {
>> + memset(bitmap, 0xff, s->bitmap_size);
>> + }
>> ret = bdrv_pwrite_sync(bs->file, s->free_data_block_offset, bitmap,
>> s->bitmap_size);
>> if (ret < 0) {
>> @@ -477,7 +675,7 @@ static int64_t alloc_block(BlockDriverState* bs,
>> int64_t sector_num)
>> if (ret < 0)
>> goto fail;
>>
>> - return get_sector_offset(bs, sector_num, 0);
>> + return get_sector_offset(bs, sector_num, false, diff);
>>
>> fail:
>> s->free_data_block_offset -= (s->block_size + s->bitmap_size);
>> @@ -501,36 +699,66 @@ static int vpc_read(BlockDriverState *bs, int64_t
>> sector_num,
>> uint8_t *buf, int nb_sectors)
>> {
>> BDRVVPCState *s = bs->opaque;
>> - int ret;
>> - int64_t offset;
>> - int64_t sectors, sectors_per_block;
>> VHDFooter *footer = (VHDFooter *) s->footer_buf;
>> + int64_t sectors_per_block = s->block_size >> BDRV_SECTOR_BITS;
>> + int64_t offset, sectors;
>> + int ret;
>>
>> - if (be32_to_cpu(footer->type) == VHD_FIXED) {
>> + switch (be32_to_cpu(footer->type)) {
>> + case VHD_FIXED:
>> return bdrv_read(bs->file, sector_num, buf, nb_sectors);
>> - }
>> - while (nb_sectors > 0) {
>> - offset = get_sector_offset(bs, sector_num, 0);
>> -
>> - sectors_per_block = s->block_size >> BDRV_SECTOR_BITS;
>> - sectors = sectors_per_block - (sector_num % sectors_per_block);
>> - if (sectors > nb_sectors) {
>> - sectors = nb_sectors;
>> - }
>> + case VHD_DYNAMIC:
>> + while (nb_sectors > 0) {
>> + sectors = sectors_per_block - (sector_num %
>> sectors_per_block);
>> + if (sectors > nb_sectors) {
>> + sectors = nb_sectors;
>> + }
>>
>> - if (offset == -1) {
>> - memset(buf, 0, sectors * BDRV_SECTOR_SIZE);
>> - } else {
>> - ret = bdrv_pread(bs->file, offset, buf,
>> - sectors * BDRV_SECTOR_SIZE);
>> - if (ret != sectors * BDRV_SECTOR_SIZE) {
>> + offset = get_sector_offset(bs, sector_num, false, false);
>> + if (offset == -1) {
>> return -1;
>> + } else if (offset == -2) {
>> + memset(buf, 0, sectors * BDRV_SECTOR_SIZE);
>> + } else {
>> + ret = bdrv_pread(bs->file, offset, buf,
>> + sectors * BDRV_SECTOR_SIZE);
>> + if (ret != sectors * BDRV_SECTOR_SIZE) {
>> + return -1;
>> + }
>> }
>> +
>> + nb_sectors -= sectors;
>> + sector_num += sectors;
>> + buf += sectors * BDRV_SECTOR_SIZE;
>> }
>> + break;
>> + case VHD_DIFF:
>> + while (nb_sectors > 0) {
>> + offset = get_sector_offset(bs, sector_num, false, true);
>> + if (offset == -1) {
>> + return -1;
>> + } else if (offset == -2) {
>> + memset(buf, 0, BDRV_SECTOR_SIZE);
>> + } else if (offset == -3) {
>> + ret = bdrv_pread(bs->backing_hd, sector_num <<
>> BDRV_SECTOR_BITS
>> + , buf, BDRV_SECTOR_SIZE);
>> + if (ret < 0) {
>> + return -1;
>> + }
>> + } else {
>> + ret = bdrv_pread(bs->file, offset, buf,
>> BDRV_SECTOR_SIZE);
>> + if (ret != BDRV_SECTOR_SIZE) {
>> + return -1;
>> + }
>> + }
>>
>> - nb_sectors -= sectors;
>> - sector_num += sectors;
>> - buf += sectors * BDRV_SECTOR_SIZE;
>> + nb_sectors--;
>> + sector_num++;
>> + buf += BDRV_SECTOR_SIZE;
>> + }
>> + break;
>> + default:
>> + return -1;
>> }
>> return 0;
>> }
>> @@ -546,44 +774,101 @@ static coroutine_fn int
>> vpc_co_read(BlockDriverState *bs, int64_t sector_num,
>> return ret;
>> }
>>
>> -static int vpc_write(BlockDriverState *bs, int64_t sector_num,
>> - const uint8_t *buf, int nb_sectors)
>> +static inline int64_t write_bitmap(BlockDriverState *bs, int64_t
>> sector_num,
>> + int64_t sectors)
>> {
>> BDRVVPCState *s = bs->opaque;
>> - int64_t offset;
>> - int64_t sectors, sectors_per_block;
>> + uint64_t offset = sector_num << BDRV_SECTOR_BITS;
>> + uint64_t bitmap_offset;
>> + uint32_t pagetable_index, pageentry_index;
>> + uint8_t bitmap[s->bitmap_size];
>> + uint32_t bitmap_index, bitmapbit_index;
>> + int i;
>> int ret;
>> - VHDFooter *footer = (VHDFooter *) s->footer_buf;
>>
>> - if (be32_to_cpu(footer->type) == VHD_FIXED) {
>> - return bdrv_write(bs->file, sector_num, buf, nb_sectors);
>> + pagetable_index = offset / s->block_size;
>> + pageentry_index = (offset % s->block_size) / 512;
>> + bitmap_offset = 512 * (uint64_t) s->pagetable[pagetable_index];
>> +
>> + if (bitmap_offset > s->max_table_entries * s->block_size) {
>> + return -1;
>> + }
>> + ret = bdrv_pread(bs->file, bitmap_offset, bitmap, s->bitmap_size);
>> + if (ret < 0) {
>> + return -1;
>> }
>> - while (nb_sectors > 0) {
>> - offset = get_sector_offset(bs, sector_num, 1);
>>
>> - sectors_per_block = s->block_size >> BDRV_SECTOR_BITS;
>> - sectors = sectors_per_block - (sector_num % sectors_per_block);
>> - if (sectors > nb_sectors) {
>> - sectors = nb_sectors;
>> + for (i = 0; i < sectors; i++) {
>> + bitmap_index = pageentry_index / 8;
>> + bitmapbit_index = 7 - pageentry_index % 8;
>> + bitmap[bitmap_index] |= (0x1 << bitmapbit_index);
>> + pageentry_index++;
>> + }
>> + ret = bdrv_pwrite(bs->file, bitmap_offset, bitmap, s->bitmap_size);
>> + if (ret < 0) {
>> + return -1;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int vpc_write(BlockDriverState *bs, int64_t sector_num,
>> + const uint8_t *buf, int nb_sectors)
>> +{
>> + BDRVVPCState *s = bs->opaque;
>> + VHDFooter *footer = (VHDFooter *) s->footer_buf;
>> + int64_t sectors_per_block = s->block_size >> BDRV_SECTOR_BITS;
>> + int64_t offset, sectors;
>> + bool diff = true;
>> + int ret = 0;
>> +
>> + switch (be32_to_cpu(footer->type)) {
>> + case VHD_FIXED:
>> + return bdrv_write(bs->file, sector_num, buf, nb_sectors);
>> + case VHD_DYNAMIC:
>> + case VHD_DIFF:
>> + if (be32_to_cpu(footer->type) == VHD_DYNAMIC) {
>> + diff = false;
>> }
>>
>> - if (offset == -1) {
>> - offset = alloc_block(bs, sector_num);
>> - if (offset < 0)
>> + while (nb_sectors > 0) {
>> + sectors = sectors_per_block - (sector_num %
>> sectors_per_block);
>> + if (sectors > nb_sectors) {
>> + sectors = nb_sectors;
>> + }
>> +
>> + offset = get_sector_offset(bs, sector_num, true, diff);
>> + if (offset == -1) {
>> return -1;
>> - }
>> + } else if (offset == -2) {
>> + offset = alloc_block(bs, sector_num, diff);
>> + if (offset < 0) {
>> + return -1;
>> + }
>> + }
>>
>> - ret = bdrv_pwrite(bs->file, offset, buf, sectors *
>> BDRV_SECTOR_SIZE);
>> - if (ret != sectors * BDRV_SECTOR_SIZE) {
>> - return -1;
>> - }
>> + ret = bdrv_pwrite(bs->file, offset, buf,
>> + sectors * BDRV_SECTOR_SIZE);
>> + if (ret != sectors * BDRV_SECTOR_SIZE) {
>> + return -1;
>> + }
>>
>> - nb_sectors -= sectors;
>> - sector_num += sectors;
>> - buf += sectors * BDRV_SECTOR_SIZE;
>> - }
>> + if (diff) {
>> + ret = write_bitmap(bs, sector_num, sectors);
>> + if (ret < 0) {
>> + return -1;
>> + }
>> + }
>>
>> - return 0;
>> + nb_sectors -= sectors;
>> + sector_num += sectors;
>> + buf += sectors * BDRV_SECTOR_SIZE;
>> + }
>> + break;
>> + default:
>> + return -1;
>> + }
>> + return ret;
>> }
>>
>> static coroutine_fn int vpc_co_write(BlockDriverState *bs, int64_t
>> sector_num,
>> @@ -911,6 +1196,7 @@ static BlockDriver bdrv_vpc = {
>> .bdrv_close = vpc_close,
>> .bdrv_reopen_prepare = vpc_reopen_prepare,
>> .bdrv_create = vpc_create,
>> + .supports_backing = true,
>>
>> .bdrv_read = vpc_co_read,
>> .bdrv_write = vpc_co_write,
>
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