the following PATCH v5 has:
1. make sure the version of VHD is bigger than 1.2, to be compatible
with VHD from vhd-utils,
because of tdbatmap.
2. Add support of w2ru.
3. Dont not support backing file chain, because need to add a more
bdvr_pread, bad to weakly performance
On Tue, Sep 23, 2014 at 10:25 PM, Xiaodong Gong <gordongong0...@gmail.com>
wrote:
> This structure is not documented in the official VHD specs, nor is the
> 'tdbatmap'
> cookie used in differencing VHDs created by Windows Server 2012. Isn't
> Hyper-V
> compatibility desired?
>
> Yepp, this structure of tdbatmap is a extra feature from vhd-util from
> Xen, here we
> could make sure the version of VHD is bigger than 1.2, I'll add it in v5.
>
> Aren't those checks required no matter what platform specific locator is
> used?
>
> Why not? IMO, w2ru (relative paths) support MUST be added before merging
> this
> feature.
>
> I think the licence of win2008 or others is a problem to me. It is hard to
> test it in
> my environment. May be a co-author of this patch is needed, do you ?
>
> What if we have a chain of differencing VHD images and the immediate parent
> does not have the required sector either, which may be at an upper level?
> Shouldn't this method be called recursively in this case?
>
> It is exactly, the vpc_open and vpc_read all should support the chain of
> snapshot.
> But the missing of cache to bat table and bitmap, performance of snapshot
> is alread
> really hard to accept. So the support to a chain is better to have after
> we have cache,
> I think.
>
> On Mon, Sep 22, 2014 at 6:26 PM, Lucian Petrut <petrutlucia...@gmail.com>
> wrote:
>
>> From: =?ISO-8859-1?B?MjFH?= <gordongong0...@gmail.com>
>>
>> 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 <gordongong0...@gmail.com>
>> ---
>> > 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 <pri...@gmail.com>
>>
>> > ---
>> > block/vpc.c | 355
>> ++++++++++++++++++++++++++++++++++++----------
>> > include/block/block_int.h | 6 +-
>> > 2 files changed, 288 insertions(+), 73 deletions(-)
>> >
>> > diff --git a/block/vpc.c b/block/vpc.c
>> > index c024b4c..2ff2bba 100644
>> > --- a/block/vpc.c
>> > +++ b/block/vpc.c
>> > @@ -33,13 +33,18 @@
>> > /**************************************************************/
>> >
>> > #define HEADER_SIZE 512
>> > +#define DYNAMIC_HEADER_SIZE 1024
>> > +#define PARENT_LOCATOR_NUM 8
>> > +#define PARENT_PREFIX_LEN 7 /* such as file:// */
>> > +#define TBBATMAP_HEAD_SIZE 28
>> > +#define PLATFORM_MACX 0x5863614d /* big endian */
>> >
>> > //#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 +143,15 @@ 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;
>> > +
>>
>> This structure is not documented in the official VHD specs, nor is the
>> 'tdbatmap'
>> cookie used in differencing VHDs created by Windows Server 2012. Isn't
>> Hyper-V
>> compatibility desired?
>>
>> > static uint32_t vpc_checksum(uint8_t* buf, size_t size)
>> > {
>> > uint32_t res = 0;
>> > @@ -153,7 +167,7 @@ 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;
>> > return 0;
>> > }
>> >
>> > @@ -164,11 +178,17 @@ 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;
>> > + int64_t data_offset = 0;
>> > + int data_length = 0;
>> > + uint32_t platform;
>> >
>> > ret = bdrv_pread(bs->file, 0, s->footer_buf, HEADER_SIZE);
>> > if (ret < 0) {
>> > @@ -176,6 +196,8 @@ 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 +252,9 @@ 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 +308,63 @@ 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 */
>> > + 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]) {
>> > + 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;
>> > +
>> > + if (platform == PLATFORM_MACX) {
>>
>> Aren't those checks required no matter what platform specific locator is
>> used?
>>
>> > + if (data_offset + PARENT_PREFIX_LEN >
>> > + s->max_table_entries * s->block_size) {
>> > + goto fail;
>> > + }
>> > + if (data_length - PARENT_PREFIX_LEN >
>> PARENT_MAX_LOCATOR) {
>> > + goto fail;
>> > + }
>> > + ret = bdrv_pread(bs->file, data_offset +
>> PARENT_PREFIX_LEN,
>> > + bs->backing_file, data_length -
>> PARENT_PREFIX_LEN);
>> > + if (ret < 0) {
>> > + goto fail;
>> > + }
>> > +
>> > + bs->backing_file[data_length - PARENT_PREFIX_LEN]
>> = '\0';
>> > + }
>> > +
>> > + if (data_offset > parent_locator_offset) {
>> > + parent_locator_offset = data_offset;
>> > + }
>> > + }
>> > +
>> > + if (strlen(bs->backing_file) == 0) {
>> > + error_setg(errp, "block-vpc: differencing is not
>> support in"
>> > + "w2ru or w2ku");
>>
>> Why not? IMO, w2ru (relative paths) support MUST be added before merging
>> this
>> feature.
>>
>> > + ret = -EINVAL;
>> > + goto fail;
>> > + }
>> > + }
>> > +
>> > + if (parent_locator_offset + 512 > s->free_data_block_offset) {
>> > + s->free_data_block_offset = parent_locator_offset + 512;
>> > + }
>> > +
>> > for (i = 0; i < s->max_table_entries; i++) {
>> > be32_to_cpus(&s->pagetable[i]);
>> > if (s->pagetable[i] != 0xFFFFFFFF) {
>> > @@ -340,35 +419,76 @@ 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.
>> > *
>> > - * The parameter write must be 1 if the offset will be used for a write
>> > - * operation (the block bitmaps is updated then), 0 otherwise.
>> > + * If error happened, -1 is returned.
>> > + *
>> > + * 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.
>> > + *
>> > + * 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 +496,7 @@ 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",
>> > // sector_num, pagetable_index, pageentry_index,
>> > // bitmap_offset, block_offset);
>> >
>> > @@ -437,7 +557,8 @@ 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 +578,11 @@ 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 +602,7 @@ 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 +626,66 @@ 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);
>>
>> What if we have a chain of differencing VHD images and the immediate
>> parent
>> does not have the required sector either, which may be at an upper level?
>> Shouldn't this method be called recursively in this case?
>>
>> > + 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 +701,101 @@ 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,
>> > @@ -910,6 +1122,7 @@ 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,
>> > diff --git a/include/block/block_int.h b/include/block/block_int.h
>> > index 8a61215..aab3ae8 100644
>> > --- a/include/block/block_int.h
>> > +++ b/include/block/block_int.h
>> > @@ -335,8 +335,10 @@ struct BlockDriverState {
>> > QLIST_HEAD(, BdrvAioNotifier) aio_notifiers;
>> >
>> > char filename[1024];
>> > - char backing_file[1024]; /* if non zero, the image is a diff of
>> > - this file image */
>> > +
>> > +#define PARENT_MAX_LOCATOR 512
>> > + char backing_file[PARENT_MAX_LOCATOR]; /* if non zero, the is a
>> diff
>> > + of this file image */
>> > char backing_format[16]; /* if non-zero and backing_file exists */
>> >
>> > QDict *full_open_options;
>>
>> block/vpc.c | 355
>> ++++++++++++++++++++++++++++++++++++----------
>> include/block/block_int.h | 6 +-
>> 2 files changed, 288 insertions(+), 73 deletions(-)
>>
>> diff --git a/block/vpc.c b/block/vpc.c
>> index c024b4c..2ff2bba 100644
>> --- a/block/vpc.c
>> +++ b/block/vpc.c
>> @@ -33,13 +33,18 @@
>> /**************************************************************/
>>
>> #define HEADER_SIZE 512
>> +#define DYNAMIC_HEADER_SIZE 1024
>> +#define PARENT_LOCATOR_NUM 8
>> +#define PARENT_PREFIX_LEN 7 /* such as file:// */
>> +#define TBBATMAP_HEAD_SIZE 28
>> +#define PLATFORM_MACX 0x5863614d /* big endian */
>>
>> //#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 +143,15 @@ 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;
>> @@ -153,7 +167,7 @@ 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;
>> return 0;
>> }
>>
>> @@ -164,11 +178,17 @@ 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;
>> + int64_t data_offset = 0;
>> + int data_length = 0;
>> + uint32_t platform;
>>
>> ret = bdrv_pread(bs->file, 0, s->footer_buf, HEADER_SIZE);
>> if (ret < 0) {
>> @@ -176,6 +196,8 @@ 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 +252,9 @@ 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 +308,63 @@ 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 */
>> + 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]) {
>> + 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;
>> +
>> + if (platform == PLATFORM_MACX) {
>> + if (data_offset + PARENT_PREFIX_LEN >
>> + s->max_table_entries * s->block_size) {
>> + goto fail;
>> + }
>> + if (data_length - PARENT_PREFIX_LEN >
>> PARENT_MAX_LOCATOR) {
>> + goto fail;
>> + }
>> + ret = bdrv_pread(bs->file, data_offset +
>> PARENT_PREFIX_LEN,
>> + bs->backing_file, data_length -
>> PARENT_PREFIX_LEN);
>> + if (ret < 0) {
>> + goto fail;
>> + }
>> +
>> + bs->backing_file[data_length - PARENT_PREFIX_LEN] =
>> '\0';
>> + }
>> +
>> + if (data_offset > parent_locator_offset) {
>> + parent_locator_offset = data_offset;
>> + }
>> + }
>> +
>> + if (strlen(bs->backing_file) == 0) {
>> + error_setg(errp, "block-vpc: differencing is not support
>> in"
>> + "w2ru or w2ku");
>> + ret = -EINVAL;
>> + goto fail;
>> + }
>> + }
>> +
>> + if (parent_locator_offset + 512 > s->free_data_block_offset) {
>> + s->free_data_block_offset = parent_locator_offset + 512;
>> + }
>> +
>> for (i = 0; i < s->max_table_entries; i++) {
>> be32_to_cpus(&s->pagetable[i]);
>> if (s->pagetable[i] != 0xFFFFFFFF) {
>> @@ -340,35 +419,76 @@ 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.
>> *
>> - * The parameter write must be 1 if the offset will be used for a write
>> - * operation (the block bitmaps is updated then), 0 otherwise.
>> + * If error happened, -1 is returned.
>> + *
>> + * 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.
>> + *
>> + * 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 +496,7 @@ 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",
>> // sector_num, pagetable_index, pageentry_index,
>> // bitmap_offset, block_offset);
>>
>> @@ -437,7 +557,8 @@ 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 +578,11 @@ 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 +602,7 @@ 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 +626,66 @@ 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 +701,101 @@ 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,
>> @@ -910,6 +1122,7 @@ 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,
>> diff --git a/include/block/block_int.h b/include/block/block_int.h
>> index 8a61215..aab3ae8 100644
>> --- a/include/block/block_int.h
>> +++ b/include/block/block_int.h
>> @@ -335,8 +335,10 @@ struct BlockDriverState {
>> QLIST_HEAD(, BdrvAioNotifier) aio_notifiers;
>>
>> char filename[1024];
>> - char backing_file[1024]; /* if non zero, the image is a diff of
>> - this file image */
>> +
>> +#define PARENT_MAX_LOCATOR 512
>> + char backing_file[PARENT_MAX_LOCATOR]; /* if non zero, the is a diff
>> + of this file image */
>> char backing_format[16]; /* if non-zero and backing_file exists */
>>
>> QDict *full_open_options;
>>
>>
>
