[PATCH v5] Support vhd type VHD_DIFFERENCING

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[PATCH v5] Support vhd type VHD_DIFFERENCING

Xiaodong Gong
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 <[hidden email]>
---
 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;
     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);
+
+            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);
+
+            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.
+ *
+ * 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",
 // 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,
--
1.8.3.1


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Re: [PATCH v5] Support vhd type VHD_DIFFERENCING

Stefan Hajnoczi
On Fri, Sep 26, 2014 at 09:43:18PM +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 <[hidden email]>
> ---
>  block/vpc.c | 428 ++++++++++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 357 insertions(+), 71 deletions(-)
Waiting for code review.

I only consider patches for the block branch that have at least 1
Reviewed-by from another contributor.

Anyone?

> 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;
>      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);
> +
> +            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);
> +
> +            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.
> + *
> + * 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",
>  // 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,
> --
> 1.8.3.1
>
>

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Re: [PATCH v5] Support vhd type VHD_DIFFERENCING

Xiaodong Gong
A little bit late for the 7 days of Nation's day, Ding xiao will review my patch. 
It looks like qcow2 is too popular. :)

On Thu, Oct 2, 2014 at 11:36 PM, Stefan Hajnoczi <[hidden email]> wrote:
On Fri, Sep 26, 2014 at 09:43:18PM +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 <[hidden email]>
> ---
>  block/vpc.c | 428 ++++++++++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 357 insertions(+), 71 deletions(-)

Waiting for code review.

I only consider patches for the block branch that have at least 1
Reviewed-by from another contributor.

Anyone?

> 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;
>      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);
> +
> +            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);
> +
> +            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.
> + *
> + * 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",
>  //   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,
> --
> 1.8.3.1
>
>