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Re: [Qemu-devel] [PATCH v3] add add-cow file format
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From: |
Robert Wang |
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Subject: |
Re: [Qemu-devel] [PATCH v3] add add-cow file format |
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Date: |
Thu, 27 Oct 2011 16:56:34 +0800 |
I re-sent the patch and use bdrv_co_flush now, thanks.
2011/10/27 shu ming <address@hidden>:
> Looks good to me. A nit, it seems that bdrv_flush is not supported anymore
> in upstream.
> bdrv_co_flush should be used instead if you update your workspace to latest
> one.
> On 2011-10-26 18:08, Robert Wang wrote:
>>
>> Please find version 4 in the attachment.
>>
>> 2011/10/23 shu ming<address@hidden>:
>>>
>>> On 2011-10-13 0:23, Dong Xu Wang wrote:
>>>>
>>>> Add add-cow file format
>>>>
>>>> Signed-off-by: Dong Xu Wang<address@hidden>
>>>> ---
>>>> Makefile.objs | 1 +
>>>> block.c | 2 +-
>>>> block.h | 1 +
>>>> block/add-cow.c | 412
>>>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>>> block_int.h | 1 +
>>>> docs/specs/add-cow.txt | 45 ++++++
>>>> 6 files changed, 461 insertions(+), 1 deletions(-)
>>>> create mode 100644 block/add-cow.c
>>>> create mode 100644 docs/specs/add-cow.txt
>>>>
>>>> diff --git a/Makefile.objs b/Makefile.objs
>>>> index c849e51..624c04c 100644
>>>> --- a/Makefile.objs
>>>> +++ b/Makefile.objs
>>>> @@ -31,6 +31,7 @@ block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
>>>>
>>>> block-nested-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o
>>>> vpc.o vvfat.o
>>>> block-nested-y += qcow2.o qcow2-refcount.o qcow2-cluster.o
>>>> qcow2-snapshot.o qcow2-cache.o
>>>> +block-nested-y += add-cow.o
>>>> block-nested-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o
>>>> qed-cluster.o
>>>> block-nested-y += qed-check.o
>>>> block-nested-y += parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o
>>>> diff --git a/block.c b/block.c
>>>> index e865fab..c25241d 100644
>>>> --- a/block.c
>>>> +++ b/block.c
>>>> @@ -106,7 +106,7 @@ int is_windows_drive(const char *filename)
>>>> #endif
>>>>
>>>> /* check if the path starts with "<protocol>:" */
>>>> -static int path_has_protocol(const char *path)
>>>> +int path_has_protocol(const char *path)
>>>> {
>>>> #ifdef _WIN32
>>>> if (is_windows_drive(path) ||
>>>> diff --git a/block.h b/block.h
>>>> index 16bfa0a..8b09f12 100644
>>>> --- a/block.h
>>>> +++ b/block.h
>>>> @@ -256,6 +256,7 @@ char *bdrv_snapshot_dump(char *buf, int buf_size,
>>>> QEMUSnapshotInfo *sn);
>>>>
>>>> char *get_human_readable_size(char *buf, int buf_size, int64_t size);
>>>> int path_is_absolute(const char *path);
>>>> +int path_has_protocol(const char *path);
>>>> void path_combine(char *dest, int dest_size,
>>>> const char *base_path,
>>>> const char *filename);
>>>> diff --git a/block/add-cow.c b/block/add-cow.c
>>>> new file mode 100644
>>>> index 0000000..d2538a2
>>>> --- /dev/null
>>>> +++ b/block/add-cow.c
>>>> @@ -0,0 +1,412 @@
>>>> +#include "qemu-common.h"
>>>> +#include "block_int.h"
>>>> +#include "module.h"
>>>> +
>>>> +#define ADD_COW_MAGIC (((uint64_t)'A'<< 56) | ((uint64_t)'D'<<
>>>> 48) | \
>>>> + ((uint64_t)'D'<< 40) | ((uint64_t)'_'<<
>>>> 32) | \
>>>> + ((uint64_t)'C'<< 24) | ((uint64_t)'O'<<
>>>> 16) | \
>>>> + ((uint64_t)'W'<< 8) | 0xFF)
>>>> +#define ADD_COW_VERSION 1
>>>> +
>>>> +typedef struct AddCowHeader {
>>>> + uint64_t magic;
>>>> + uint32_t version;
>>>> + char backing_file[1024];
>>>> + char image_file[1024];
>>>
>>> 1024 is a magic number for me. Can we have a meaningful macro?
>>>
>>>
>>>> + uint64_t size;
>>>> +} QEMU_PACKED AddCowHeader;
>>>> +
>>>> +typedef struct BDRVAddCowState {
>>>> + char image_file[1024];
>>>> + BlockDriverState *image_hd;
>>>> + uint8_t *bitmap;
>>>> + uint64_t bitmap_size;
>>>> +} BDRVAddCowState;
>>>> +
>>>> +static int add_cow_probe(const uint8_t *buf, int buf_size, const char
>>>> *filename)
>>>> +{
>>>> + const AddCowHeader *header = (const void *)buf;
>>>> +
>>>> + if (be64_to_cpu(header->magic) == ADD_COW_MAGIC&&
>>>> + be32_to_cpu(header->version) == ADD_COW_VERSION) {
>>>> + return 100;
>>>> + } else {
>>>> + return 0;
>>>> + }
>>>> +}
>>>> +
>>>> +static int add_cow_open(BlockDriverState *bs, int flags)
>>>> +{
>>>> + AddCowHeader header;
>>>> + int64_t size;
>>>> + char image_filename[1024];
>>>> + int image_flags;
>>>> + BlockDriver *image_drv = NULL;
>>>> + int ret;
>>>> + BDRVAddCowState *state = (BDRVAddCowState *)(bs->opaque);
>>>> +
>>>> + ret = bdrv_pread(bs->file, 0,&header, sizeof(header));
>>>> + if (ret != sizeof(header)) {
>>>> + goto fail;
>>>> + }
>>>> +
>>>> + if (be64_to_cpu(header.magic) != ADD_COW_MAGIC ||
>>>> + be32_to_cpu(header.version) != ADD_COW_VERSION) {
>>>> + ret = -1;
>>>> + goto fail;
>>>> + }
>>>> +
>>>> + size = be64_to_cpu(header.size);
>>>> + bs->total_sectors = size / BDRV_SECTOR_SIZE;
>>>> +
>>>> + QEMU_BUILD_BUG_ON(sizeof(state->image_file) !=
>>>> sizeof(header.image_file));
>>>> + pstrcpy(bs->backing_file, sizeof(bs->backing_file),
>>>> + header.backing_file);
>>>> + pstrcpy(state->image_file, sizeof(state->image_file),
>>>> + header.image_file);
>>>> +
>>>> + state->bitmap_size = ((bs->total_sectors + 7)>> 3);
>>>> + state->bitmap = g_malloc0(state->bitmap_size);
>>>> +
>>>> + ret = bdrv_pread(bs->file, sizeof(header), state->bitmap,
>>>> + state->bitmap_size);
>>>> + if (ret != state->bitmap_size) {
>>>> + goto fail;
>>>> + }
>>>> + /* If there is a image_file, must be together with backing_file */
>>>> + if (state->image_file[0] != '\0') {
>>>> + state->image_hd = bdrv_new("");
>>>> + /* Relative to image or working dir, need discussion */
>>>> + if (path_has_protocol(state->image_file)) {
>>>> + pstrcpy(image_filename, sizeof(image_filename),
>>>> + state->image_file);
>>>> + } else {
>>>> + path_combine(image_filename, sizeof(image_filename),
>>>> + bs->filename, state->image_file);
>>>> + }
>>>> +
>>>> + image_drv = bdrv_find_format("raw");
>>>> + image_flags =
>>>> + (flags& (~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING))) |
>>>> BDRV_O_RDWR;
>>>> + state->image_hd->keep_read_only = 0;
>>>> +
>>>> + ret = bdrv_open(state->image_hd, image_filename, image_flags,
>>>> + image_drv);
>>>> + if (ret< 0) {
>>>> + goto fail;
>>>> + }
>>>> + } else {
>>>> + ret = -ENOENT;
>>>> + goto fail;
>>>> + }
>>>> + return 0;
>>>> + fail:
>>>> + if (state->bitmap) {
>>>> + g_free(state->bitmap);
>>>> + state->bitmap = NULL;
>>>> + }
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static inline void add_cow_set_bit(BlockDriverState *bs, int64_t
>>>> bitnum)
>>>> +{
>>>> + uint64_t offset = bitnum / 8;
>>>> + BDRVAddCowState *state = (BDRVAddCowState *)(bs->opaque);
>>>> + state->bitmap[offset] |= (1<< (bitnum % 8));
>>>> +}
>>>> +
>>>> +static inline int is_bit_set(BlockDriverState *bs, int64_t bitnum)
>>>> +{
>>>> + BDRVAddCowState *state = (BDRVAddCowState *)(bs->opaque);
>>>> + uint64_t offset = bitnum / 8;
>>>> + return !!(state->bitmap[offset]& (1<< (bitnum % 8)));
>>>> +}
>>>> +
>>>> +static int add_cow_is_allocated(BlockDriverState *bs, int64_t
>>>> sector_num,
>>>> + int nb_sectors, int *num_same)
>>>> +{
>>>> + int changed;
>>>> + uint64_t bitmap_size = ((BDRVAddCowState
>>>> *)(bs->opaque))->bitmap_size;
>>>> +
>>>> + /* Beyond the end of bitmap, return error or read from
>>>> backing_file?
>>>> */
>>>> + if (((sector_num + nb_sectors + 7) / 8)> bitmap_size) {
>>>> + return 0;
>>>> + }
>>>> +
>>>> + if (nb_sectors == 0) {
>>>> + *num_same = nb_sectors;
>>>> + return 0;
>>>> + }
>>>> +
>>>> + changed = is_bit_set(bs, sector_num);
>>>> + if (changed< 0) {
>>>> + return 0;
>>>> + }
>>>> +
>>>> + for (*num_same = 1; *num_same< nb_sectors; (*num_same)++) {
>>>> + if (is_bit_set(bs, sector_num + *num_same) != changed) {
>>>> + break;
>>>> + }
>>>> + }
>>>> +
>>>> + return changed;
>>>> +}
>>>> +
>>>> +static int add_cow_update_bitmap(BlockDriverState *bs, int64_t
>>>> sector_num,
>>>> + int nb_sectors)
>>>> +{
>>>> + int i, ret = 0;
>>>> + BDRVAddCowState *state = (BDRVAddCowState *)(bs->opaque);
>>>> + uint64_t start_pos = sector_num / 8;
>>>> + uint64_t end_pos = (sector_num + nb_sectors - 1) / 8;
>>>> +
>>>> + if (start_pos> state->bitmap_size) {
>>>> + return -1;
>>>> + }
>>>> +
>>>> + for (i = 0; i< nb_sectors; i++) {
>>>> + add_cow_set_bit(bs, sector_num + i);
>>>> + }
>>>> + ret = bdrv_pwrite_sync(bs->file,
>>>> + sizeof(AddCowHeader) + start_pos,
>>>> + state->bitmap + start_pos,
>>>> + MIN(((end_pos - start_pos)& (~512)) + 512,
>>>> state->bitmap_size -
>>>> start_pos));
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static void add_cow_close(BlockDriverState *bs)
>>>> +{
>>>> + BDRVAddCowState *state = (BDRVAddCowState *)(bs->opaque);
>>>> + if (state->bitmap) {
>>>> + g_free(state->bitmap);
>>>> + state->bitmap = NULL;
>>>> + }
>>>> +}
>>>> +
>>>> +static int add_cow_create(const char *filename, QEMUOptionParameter
>>>> *options)
>>>> +{
>>>> + AddCowHeader header;
>>>> + int64_t image_sectors = 0;
>>>> + const char *backing_filename = NULL;
>>>> + const char *image_filename = NULL;
>>>> + int ret;
>>>> + BlockDriverState *bs, *image_bs = NULL;
>>>> +
>>>> + while (options&& options->name) {
>>>> + if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
>>>> + image_sectors = options->value.n / BDRV_SECTOR_SIZE;
>>>> + } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
>>>> + backing_filename = options->value.s;
>>>> + } else if (!strcmp(options->name, BLOCK_OPT_IMAGE_FILE)) {
>>>> + image_filename = options->value.s;
>>>> + }
>>>> + options++;
>>>> + }
>>>> +
>>>> + if (!backing_filename || !image_filename) {
>>>> + return -EINVAL;
>>>> + }
>>>> + /* Make sure image file exists */
>>>> + ret = bdrv_file_open(&image_bs, image_filename, BDRV_O_RDWR
>>>> + | BDRV_O_CACHE_WB);
>>>> + if (ret< 0) {
>>>> + return ret;
>>>> + }
>>>> + bdrv_close(image_bs);
>>>> + ret = bdrv_create_file(filename, NULL);
>>>> + if (ret< 0) {
>>>> + return ret;
>>>> + }
>>>> +
>>>> + ret = bdrv_file_open(&bs, filename, BDRV_O_RDWR);
>>>> + if (ret< 0) {
>>>> + return ret;
>>>> + }
>>>> +
>>>> + memset(&header, 0, sizeof(header));
>>>> + header.magic = cpu_to_be64(ADD_COW_MAGIC);
>>>> + header.version = cpu_to_be32(ADD_COW_VERSION);
>>>> + pstrcpy(header.backing_file, sizeof(header.backing_file),
>>>> backing_filename);
>>>> + pstrcpy(header.image_file, sizeof(header.image_file),
>>>> image_filename);
>>>> + header.size = cpu_to_be64(image_sectors * BDRV_SECTOR_SIZE);
>>>> +
>>>> + ret = bdrv_pwrite(bs, 0,&header, sizeof(header));
>>>> + if (ret< 0) {
>>>> + bdrv_close(bs);
>>>> + return ret;
>>>> + }
>>>> + bdrv_close(bs);
>>>> +
>>>> + BlockDriver *drv = bdrv_find_format("add-cow");
>>>> + assert(drv != NULL);
>>>> + ret = bdrv_open(bs, filename, BDRV_O_RDWR | BDRV_O_NO_FLUSH, drv);
>>>> + if (ret< 0) {
>>>> + return ret;
>>>> + }
>>>> +
>>>> + ret = bdrv_truncate(bs, image_sectors * BDRV_SECTOR_SIZE);
>>>> +fail:
>>>
>>> "fail" label is not used in this function.
>>>
>>>
>>>> + bdrv_close(bs);
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static int add_cow_co_readv(BlockDriverState *bs, int64_t sector_num,
>>>> + int remaining_sectors, QEMUIOVector *qiov)
>>>> +{
>>>> + BDRVAddCowState *s = bs->opaque;
>>>> + int cur_nr_sectors;
>>>> + uint64_t bytes_done = 0;
>>>> + QEMUIOVector hd_qiov;
>>>> + int n, ret = 0;
>>>> +
>>>> + qemu_iovec_init(&hd_qiov, qiov->niov);
>>>> + while (remaining_sectors != 0) {
>>>> + cur_nr_sectors = remaining_sectors;
>>>> + if (add_cow_is_allocated(bs, sector_num, cur_nr_sectors,&n)) {
>>>> + cur_nr_sectors = n;
>>>> + qemu_iovec_reset(&hd_qiov);
>>>> + qemu_iovec_copy(&hd_qiov, qiov, bytes_done,
>>>> + cur_nr_sectors * BDRV_SECTOR_SIZE);
>>>> + ret = bdrv_co_readv(s->image_hd, sector_num, n,&hd_qiov);
>>>> + if (ret< 0) {
>>>> + goto fail;
>>>> + }
>>>> + } else {
>>>> + cur_nr_sectors = n;
>>>> + if (bs->backing_hd) {
>>>> + qemu_iovec_reset(&hd_qiov);
>>>> + qemu_iovec_copy(&hd_qiov, qiov, bytes_done,
>>>> + cur_nr_sectors * BDRV_SECTOR_SIZE);
>>>> + ret = bdrv_co_readv(bs->backing_hd, sector_num,
>>>> + n,&hd_qiov);
>>>> + if (ret< 0) {
>>>> + goto fail;
>>>> + }
>>>> + } else {
>>>> + qemu_iovec_reset(&hd_qiov);
>>>> + qemu_iovec_memset(&hd_qiov, 0,
>>>> + BDRV_SECTOR_SIZE * cur_nr_sectors);
>>>> + }
>>>> + }
>>>> + remaining_sectors -= cur_nr_sectors;
>>>> + sector_num += cur_nr_sectors;
>>>> + bytes_done += cur_nr_sectors * BDRV_SECTOR_SIZE;
>>>> + }
>>>> +fail:
>>>> + qemu_iovec_destroy(&hd_qiov);
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static int add_cow_co_writev(BlockDriverState *bs, int64_t sector_num,
>>>> + int remaining_sectors, QEMUIOVector *qiov)
>>>> +{
>>>> + BDRVAddCowState *s = bs->opaque;
>>>> + int ret = 0;
>>>> + QEMUIOVector hd_qiov;
>>>> + qemu_iovec_init(&hd_qiov, qiov->niov);
>>>> +
>>>
>>> It looks like that the memory where "bs" is pointing to should be
>>> protected
>>> by a lock. Because "bs"
>>> was passed to several BlockDriver entries like ".bdrv_co_writev',
>>> 'bdrv_co_readv'&etc which can be executed
>>> in parallel to access the memory where "bs" is pointing to.
>>>
>>>> + qemu_iovec_reset(&hd_qiov);
>>>> + qemu_iovec_copy(&hd_qiov, qiov, 0, remaining_sectors *
>>>> BDRV_SECTOR_SIZE);
>>>> + ret = bdrv_co_writev(s->image_hd,
>>>> + sector_num,
>>>> + remaining_sectors,&hd_qiov);
>>>> + if (ret< 0) {
>>>> + goto fail;
>>>> + }
>>>> +
>>>> + ret = add_cow_update_bitmap(bs, sector_num, remaining_sectors);
>>>> + if (ret< 0) {
>>>> + goto fail;
>>>> + }
>>>> +fail:
>>>> + qemu_iovec_destroy(&hd_qiov);
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static int bdrv_add_cow_truncate(BlockDriverState *bs, int64_t offset)
>>>> +{
>>>> + int ret = 0;
>>>> + int64_t image_sectors = offset/BDRV_SECTOR_SIZE;
>>>> + int64_t be_offset = cpu_to_be64(offset);
>>>> + BDRVAddCowState *state = bs->opaque;
>>>> + ret = bdrv_truncate(bs->file, ((image_sectors + 7)>> 3)
>>>> + + sizeof(AddCowHeader));
>>>> + if (ret< 0) {
>>>> + return ret;
>>>> + }
>>>> +
>>>> + ret = bdrv_pwrite_sync(bs->file, offsetof(AddCowHeader, size),
>>>> +&be_offset, sizeof(uint64_t));
>>>> + if (ret< 0) {
>>>> + return ret;
>>>> + }
>>>> +
>>>> + ret = bdrv_truncate(state->image_hd, offset);
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static QEMUOptionParameter add_cow_create_options[] = {
>>>> + {
>>>> + .name = BLOCK_OPT_SIZE,
>>>> + .type = OPT_SIZE,
>>>> + .help = "Virtual disk size"
>>>> + },
>>>> + {
>>>> + .name = BLOCK_OPT_BACKING_FILE,
>>>> + .type = OPT_STRING,
>>>> + .help = "File name of a base image"
>>>> + },
>>>> + {
>>>> + .name = BLOCK_OPT_IMAGE_FILE,
>>>> + .type = OPT_STRING,
>>>> + .help = "File name of a image file"
>>>> + },
>>>> + { NULL }
>>>> +};
>>>> +
>>>> +static int add_cow_flush(BlockDriverState *bs)
>>>> +{
>>>> + BDRVAddCowState *state = bs->opaque;
>>>> + int ret = bdrv_flush(state->image_hd);
>>>> + if (ret< 0) {
>>>> + return ret;
>>>> + }
>>>> + return bdrv_flush(bs->file);
>>>> +}
>>>> +
>>>> +static BlockDriverAIOCB *add_cow_aio_flush(BlockDriverState *bs,
>>>> + BlockDriverCompletionFunc *cb, void *opaque)
>>>> +{
>>>> + BDRVAddCowState *state = bs->opaque;
>>>> + int ret = bdrv_flush(state->image_hd);
>>>> + if (ret< 0) {
>>>> + return NULL;
>>>> + }
>>>> +
>>>> + return bdrv_aio_flush(bs->file, cb, opaque);
>>>> +}
>>>> +
>>>> +static BlockDriver bdrv_add_cow = {
>>>> + .format_name = "add-cow",
>>>> + .instance_size = sizeof(BDRVAddCowState),
>>>> + .bdrv_probe = add_cow_probe,
>>>> + .bdrv_open = add_cow_open,
>>>> + .bdrv_close = add_cow_close,
>>>> + .bdrv_create = add_cow_create,
>>>> + .bdrv_is_allocated = add_cow_is_allocated,
>>>> +
>>>> + .bdrv_co_readv = add_cow_co_readv,
>>>> + .bdrv_co_writev = add_cow_co_writev,
>>>> + .bdrv_truncate = bdrv_add_cow_truncate,
>>>> +
>>>> + .create_options = add_cow_create_options,
>>>> + .bdrv_flush = add_cow_flush,
>>>> + .bdrv_aio_flush = add_cow_aio_flush,
>>>> +};
>>>> +
>>>> +static void bdrv_add_cow_init(void)
>>>> +{
>>>> + bdrv_register(&bdrv_add_cow);
>>>> +}
>>>> +
>>>> +block_init(bdrv_add_cow_init);
>>>> diff --git a/block_int.h b/block_int.h
>>>> index 8c3b863..2b26fdc 100644
>>>> --- a/block_int.h
>>>> +++ b/block_int.h
>>>> @@ -42,6 +42,7 @@
>>>> #define BLOCK_OPT_TABLE_SIZE "table_size"
>>>> #define BLOCK_OPT_PREALLOC "preallocation"
>>>> #define BLOCK_OPT_SUBFMT "subformat"
>>>> +#define BLOCK_OPT_IMAGE_FILE "image_file"
>>>>
>>>> typedef struct AIOPool {
>>>> void (*cancel)(BlockDriverAIOCB *acb);
>>>> diff --git a/docs/specs/add-cow.txt b/docs/specs/add-cow.txt
>>>> new file mode 100644
>>>> index 0000000..0443c6c
>>>> --- /dev/null
>>>> +++ b/docs/specs/add-cow.txt
>>>> @@ -0,0 +1,45 @@
>>>> +== General ==
>>>> +
>>>> +Raw file format does not support backing_file and copy on write
>>>> feature.
>>>> Then
>>>> +you can use add-cow file realize these features.
>>>> +
>>>> +When using add-cow, procedures may like this:
>>>> +(ubuntu.img is a disk image which has been installed OS.)
>>>> + 1) Create a raw image with the same size of ubuntu.img
>>>> + qemu-img create -f raw test.raw 8G
>>>> + 2) Create a add-cow image which will store dirty bitmap
>>>> + qemu-img create -f add-cow test.add-cow -o
>>>> backing_file=ubuntu.img,image_file=test.raw
>>>> + 3) Run qemu with add-cow image
>>>> + qemu -drive if=virtio,file=test.add-cow
>>>> +
>>>> +=Specification=
>>>> +
>>>> +The file format looks like this:
>>>> +
>>>> + +----------+----------+----------+-----+
>>>> + | Header | Data | Data | ... |
>>>> + +----------+----------+----------+-----+
>>>> +
>>>> + All numbers in add-cow are stored in Big Endian byte order.
>>>> +
>>>> +
>>>> +== Header ==
>>>> +
>>>> +The Header is included in the first bytes:
>>>> +
>>>> + Byte 0 - 7: magic
>>>> + add-cow magic string ("ADD_COW\xff")
>>>> +
>>>> + 8 - 11: version
>>>> + Version number (only valid value is 1 now)
>>>> +
>>>> + 12 - 1035: backing_file
>>>> + backing_file file name related to add-cow file.
>>>> While
>>>> + using backing_file, must together with
>>>> image_file.
>>>> +
>>>> + 1036 - 2059: image_file
>>>> + image_file is a raw file, While using
>>>> image_file,
>>>> must
>>>> + together with image_file.
>>>> +
>>>> + 2060 - 2067: size
>>>> + Virtual disk size of image_file in bytes.
>>>
>>>
>>>
>>
>>
>
>
>
--
Regards
Robert Wang