0002-Support-vhd-type-VHD_DIFFERENCING.patchDescription: Binary data
|
| From: | Gordon Gong |
| Subject: | [Qemu-devel] [RFC PATCH v2] Support vhd type VHD_DIFFERENCING |
| Date: | Thu, 4 Sep 2014 22:49:43 +0800 |
[Qemu-devel][RFC PATCH v2] Support vhd type VHD_DIFFERENCING
From 5387a2a7b6ad052659a08a1fc7e89595708396d1 Mon Sep 17 00:00:00 2001
From: Xiaodong Gong <address@hidden>
Date: Thu, 4 Sep 2014 01:14:59 +0800
Subject: [PATCH 2/2] Support vhd type VHD_DIFFERENCING
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 | 329 +++++++++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 261 insertions(+), 68 deletions(-)
diff --git a/block/vpc.c b/block/vpc.c
index c024b4c..3ba0d57 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 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 +308,56 @@ 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 (MACX == platform) {
+ if (data_offset + PARENT_PREFIX_LEN >
+ s->max_table_entries * s->block_size) {
+ goto fail;
+ }
+ if (data_length - PARENT_PREFIX_LEN > 1024) {
+ 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 (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) {
@@ -363,19 +435,6 @@ static inline int64_t get_sector_offset(BlockDriverState *bs,
bitmap_offset = 512 * (uint64_t) s->pagetable[pagetable_index];
block_offset = bitmap_offset + s->bitmap_size + (512 * pageentry_index);
- // 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)) {
- uint8_t bitmap[s->bitmap_size];
-
- s->last_bitmap_offset = bitmap_offset;
- memset(bitmap, 0xff, s->bitmap_size);
- bdrv_pwrite_sync(bs->file, bitmap_offset, bitmap, s->bitmap_size);
- }
-
// printf("sector: %" PRIx64 ", index: %x, offset: %x, bioff: %" PRIx64 ", bloff: %" PRIx64 "\n",
// sector_num, pagetable_index, pageentry_index,
// bitmap_offset, block_offset);
@@ -412,6 +471,53 @@ static inline int64_t get_sector_offset(BlockDriverState *bs,
}
/*
+ * Returns the absolute byte offset of the given sector in the differencing
+ * image file.
+ *
+ * If the sector is not allocated, -1 is returned instead. If the sector is
+ * allocated in the backing file, -2 is returned. If the sector is allocated
+ * in current file, the block offset is returned.
+ */
+static inline int64_t get_sector_offset_diff(BlockDriverState *bs,
+ int64_t sector_num)
+{
+ BDRVVPCState *s = bs->opaque;
+ uint64_t offset = sector_num << BDRV_SECTOR_BITS;
+ uint64_t bitmap_offset;
+ uint64_t block_offset;
+ uint32_t pagetable_index, pageentry_index;
+ uint32_t bitmap_index, bitmapentry_index;
+ uint8_t bitmap[s->bitmap_size];
+ int ret;
+
+ pagetable_index = offset / s->block_size;
+ if (pagetable_index >= s->max_table_entries) {
+ return -1;
+ } else if (0xffffffff == s->pagetable[pagetable_index]) {
+ return -2;
+ }
+
+ 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;
+ }
+
+ pageentry_index = (offset % s->block_size) / 512;
+ 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 + (512 * pageentry_index);
+ return block_offset;
+ } else {
+ return -2;
+ }
+}
+
+/*
* Writes the footer to the end of the image file. This is needed when the
* file grows as it overwrites the old footer
*
@@ -437,7 +543,8 @@ 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 isdiff)
{
BDRVVPCState *s = bs->opaque;
int64_t bat_offset;
@@ -457,7 +564,11 @@ 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 (isdiff) {
+ 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) {
@@ -501,36 +612,62 @@ 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) {
- return -1;
+ offset = get_sector_offset(bs, sector_num, 0);
+ if (-1 == offset) {
+ 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_diff(bs, sector_num);
+ if (-1 == offset) {
+ memset(buf, 0, BDRV_SECTOR_SIZE);
+ } else if (-2 == offset) {
+ 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;
}
@@ -546,43 +683,98 @@ static coroutine_fn int vpc_co_read(BlockDriverState *bs, int64_t sector_num,
return ret;
}
+static inline int64_t write_bitmap(BlockDriverState *bs, int64_t sector_num,
+ int64_t sectors)
+{
+ BDRVVPCState *s = bs->opaque;
+ 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;
+
+ 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;
+ }
+
+ 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;
- 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;
+ bool isdiff = true;
int ret;
- VHDFooter *footer = (VHDFooter *) s->footer_buf;
- if (be32_to_cpu(footer->type) == VHD_FIXED) {
+ switch (be32_to_cpu(footer->type)) {
+ case VHD_FIXED:
return bdrv_write(bs->file, sector_num, buf, nb_sectors);
- }
- 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;
+ case VHD_DYNAMIC:
+ case VHD_DIFF:
+ if (VHD_DYNAMIC == be32_to_cpu(footer->type)) {
+ isdiff = 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, 1);
+ if (offset == -1) {
+ offset = alloc_block(bs, sector_num, isdiff);
+ 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;
- }
+ if (true == isdiff) {
+ ret = write_bitmap(bs, sector_num, sectors);
+ if (ret < 0) {
+ return -1;
+ }
+ }
- nb_sectors -= sectors;
- sector_num += sectors;
- buf += sectors * BDRV_SECTOR_SIZE;
+ nb_sectors -= sectors;
+ sector_num += sectors;
+ buf += sectors * BDRV_SECTOR_SIZE;
+ }
+ break;
+ default:
+ return -1;
}
-
return 0;
}
@@ -910,6 +1102,7 @@ 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
1. bdrv_preadv and bdrv_pwritev affer get_sector_offset_* is already checked, others are checked if
version 2.
2. MACX is a big-endian number, so there is no need be32_to_cpu, but I added a comment to MACX.
3. clean the code no used after in vpc_open.
4. move bdrv_co_readv() to bdrv_preadv in vpc_read.
5. Added some code to make it easy to understand.
6. the wrong use of cpu_to_be32 is fixed with another patch.
-------------------------------------------------------------------------------------------------------------------
On Tue, Jul 01, 2014 at 05:45:19PM +0800, Ding xiao wrote:
Sorry for the delay, I forgot about this patch.
> +typedef struct vhd_tdbatmap_header {
> + char magic[8]; /* "tdbatmap"*/
> +
> + /* byte offset to batmap*/
> + uint64_t batmap_offset;
> +
> + /* Offset of the Block Allocation Table (BAT)*/
This comment describes the batmap_offset field? Maybe this should be
dropped since that field already has a comment.
> + /* read backend file*/
> + 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);
> + if (dyndisk_header->parent_locator[i].platform == MACX) {
Missing be32_to_cpu()?
> + ret = bdrv_pread(bs->file, data_offset + 7,
> + bs->backing_file, data_length - 7);
Buffer overflow: char bs->backing_file[1024].
All input must be validated!
> + if (ret < 0) {
> + goto fail;
> + }
> + bs->backing_file[data_length - 7] = '\0';
Memory corruption if data_length < 7. Missing input validation.
> + }
> + if (data_offset > parent_locator_offset) {
> + parent_locator_offset = data_offset;
> + }
> + }
> + }
> +
> + 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) {
> @@ -364,6 +425,9 @@ static inline int64_t get_sector_offset(BlockDriverState
> *bs,
> // 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.
> +
> + /*this will not use*/
> +#if 0
Delete the code if it is no longer used.
> @@ -433,7 +498,7 @@ 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, int
> diff)
Please use the C99 bool type since it communicates more clearly that
diff is either true or false (not a counter or bitmap).
It would be clearest to check footer->type for VHD_DIFFERENCING in this
function instead of adding a new argument to the function.
> @@ -501,33 +611,64 @@ static int vpc_read(BlockDriverState *bs, int64_t
> sector_num,
> int64_t offset;
> int64_t sectors, sectors_per_block;
> VHDFooter *footer = (VHDFooter *) s->footer_buf;
> + QEMUIOVector hd_qiov;
> + struct iovec qiov;
>
> if (cpu_to_be32(footer->type) == VHD_FIXED) {
> return bdrv_read(bs->file, sector_num, buf, nb_sectors);
> - }
> - while (nb_sectors > 0) {
> - offset = get_sector_offset(bs, sector_num, 0);
> + } else if (cpu_to_be32(footer->type) == VHD_DYNAMIC) {
cpu_to_be32() is wrong since VHD_DYNAMIC is an enum constant (just a
regular CPU-endian integer).
Please add a separate patch before this one that cleans up incorrect
cpu_to_be*() usage. For example, cpu_to_be32(footer->type) == VHD_FIXED
a few lines above is wrong too.
> + 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;
> + }
>
> - 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;
> + 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) {
Indentation is off
> + return -1;
> + }
> + }
> +
> + nb_sectors -= sectors;
> + sector_num += sectors;
> + buf += sectors * BDRV_SECTOR_SIZE;
> }
> + } else {
> + while (nb_sectors > 0) {
> + offset = get_sector_offset_diff(bs, sector_num);
> + if (offset == -1) {
> + memset(buf, 0, BDRV_SECTOR_SIZE);
> + } else if (offset == -2) {
> + qiov.iov_base = (void *)buf;
This cast is unnecessary. The compiler does not warn about pointer
casts to or from void*.
> + qiov.iov_len = 512;
> + hd_qiov.iov = &qiov;
> + hd_qiov.niov = 1;
> + hd_qiov.nalloc = -1;
> + hd_qiov.size = 512;
This is not idiomatic. Normally 'qiov' is a QEMUIOVector, not a struct
iovec. The qemu_iovec_*() functions should be used instead of manually
setting QEMUIOVector fields:
iov.iov_base = buf;
iov.iov_len = 512;
qemu_iovec_init_external(&hd_qiov, &iov, 1);
> + ret = bdrv_co_readv(bs->backing_hd, sector_num, 1, &hd_qiov);
> + if (ret < 0) {
> + return -1;
> + }
Why are you using bdrv_co_readv() instead of bdrv_pread() like the rest
of this file?
It would be simpler to use bdrv_pread(). Then you don't need the struct
iovec and QEMUIOVector. This function also hasn't been marked
coroutine_fn yet, so it is cleaner to stick with bdrv_pread() until the
file is properly converted to coroutines.
0002-Support-vhd-type-VHD_DIFFERENCING.patch
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