Am 09.09.2011 07:48, schrieb Dong Xu Wang:
> As raw file format does not support backing_file and copy on write feature,
> so
> I add COW to it to support backing_file option. I store dirty bitmap in an
> add-cow file. When executed, it looks like this:
> qemu-img create -f add-cow -o backing_file=ubuntu.img,image_file=test.img
> test.add-cow
> qemu -drive if=virtio,file=test.add-cow -m 1024
>
> (test.img is a raw format file; test.add-cow stores bitmap)
>
> Signed-off-by: Dong Xu Wang <wdon...@linux.vnet.ibm.com>
You should not make any changes to generic code, except maybe add
something to bdrv_get_info(). In particular you shouldn't need to touch
bdrv_open() or bdrv_create() at all.
The one required change in the approach for this to work is that you
shouldn't view raw+add_cow as a unit, but add_cow should be treated as
something separate that happens to be stacked on a raw file (which is
created separately).
Then you can do almost everything in block/add-cow.c.
> ---
> Makefile.objs | 1 +
> block.c | 83 ++++++++++-
> block.h | 2 +
> block/add-cow.c | 456
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> block_int.h | 6 +
> qemu-img.c | 10 ++
> 6 files changed, 555 insertions(+), 3 deletions(-)
> create mode 100644 block/add-cow.c
>
> diff --git a/Makefile.objs b/Makefile.objs
> index 26b885b..1402f9f 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 a8c789a..c797cfc 100644
> --- a/block.c
> +++ b/block.c
> @@ -369,7 +369,7 @@ static int find_image_format(const char *filename,
> BlockDriver **pdrv)
> {
> int ret, score, score_max;
> BlockDriver *drv1, *drv;
> - uint8_t buf[2048];
> + uint8_t buf[4096];
> BlockDriverState *bs;
What's the reason for this change?
> diff --git a/block/add-cow.c b/block/add-cow.c
> new file mode 100644
> index 0000000..f4b67e5
> --- /dev/null
> +++ b/block/add-cow.c
> @@ -0,0 +1,456 @@
> +#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
> +
> +struct add_cow_header {
> + uint64_t magic;
> + uint32_t version;
> + char backing_file[1024];
> + char image_file[1024];
> + uint64_t size;
> + uint32_t sectorsize;
> +} add_cow_header;
QEMU_PACKED
> +typedef struct BDRVAddCowState {
> + CoMutex lock;
> + CoMutex bitmap_lock;
> +} BDRVAddCowState;
> +
> +typedef struct AddCowAIOCB {
> + BlockDriverAIOCB common;
> + int64_t sector_num;
> + QEMUIOVector *qiov;
> + int remaining_sectors;
> + int cur_nr_sectors;
> + uint64_t bytes_done;
> + bool is_write;
> + QEMUIOVector hd_qiov;
> + QEMUBH *bh;
> +
> +} AddCowAIOCB;
You shouldn't be using AIOCBs with a coroutine-based block driver.
Instead you should just use variables on the stack and function parameters.
> +static int add_cow_flush(BlockDriverState *bs)
> +{
> + return bdrv_flush(bs->file);
> +}
What about bs->image_hd?
> @@ -208,6 +209,11 @@ struct BlockDriverState {
> int in_use; /* users other than guest access, eg. block migration */
> QTAILQ_ENTRY(BlockDriverState) list;
> void *private;
> +
> + char image_file[1024];
> + BlockDriverState *image_hd;
> + uint8_t *bitmap;
> + uint64_t bitmap_size;
> };
These belong in BDRVAddCowState.
Kevin
