Re: [Qemu-devel] [PATCH v3] add add-cow file format

[shu ming <shuming@linux.vnet.ibm.com>]

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<shuming@linux.vnet.ibm.com>:
>> On 2011-10-13 0:23, Dong Xu Wang wrote:
>>> Add add-cow file format
>>>
>>> Signed-off-by: Dong Xu Wang<wdongxu@linux.vnet.ibm.com>
>>> ---
>>>   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.
>>
>>
>>
>
>