Re: [Qemu-devel] [RFC PATCH v3] Support vhd type VHD_DIFFERENCING

[Stefan Hajnoczi]

On Wed, Sep 10, 2014 at 09:32:15PM +0800, 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>
> ---
>  block/vpc.c               | 355 
> ++++++++++++++++++++++++++++++++++++----------
>  include/block/block_int.h |   6 +-
>  2 files changed, 288 insertions(+), 73 deletions(-)

Philipp, any comments on v3?

> 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;
> -- 
> 1.8.3.1
>

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