Re: [Qemu-devel] [RFC PATCH 04/12] qcow2/dirty-bitmaps: load IN_USE bitmaps if disk is RO

[Vladimir Sementsov-Ogievskiy]

12.05.2018 04:25, John Snow wrote:
> For the purposes of qemu-img manipulation and querying of bitmaps, load
> bitmaps that are "in use" -- if the image is read only. This will allow
> us to diagnose problems with this flag using the qemu-img tool.

It looks unsafe.. We can load them, then reopen rw and then store them 
on vm close, the result would be unpredictable. And they become 
available for qmp commands..

If we want to load them, we may need some additional state for such 
dirty bitmaps, something like "invalid", to be sure, that they will not 
be used like normal bitmap. And we may
need some additional flag to load or not load them, and this behavior 
will be unrelated to can_write().

> Signed-off-by: John Snow <address@hidden>
> ---
>   block/qcow2-bitmap.c | 32 +++++++++++++++-----------------
>   1 file changed, 15 insertions(+), 17 deletions(-)
>
> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
> index fc8d52fc3e..b556dbdccd 100644
> --- a/block/qcow2-bitmap.c
> +++ b/block/qcow2-bitmap.c
> @@ -346,7 +346,7 @@ static BdrvDirtyBitmap *load_bitmap(BlockDriverState *bs,
>       uint32_t granularity;
>       BdrvDirtyBitmap *bitmap = NULL;
>   
> -    if (bm->flags & BME_FLAG_IN_USE) {
> +    if (can_write(bs) && (bm->flags & BME_FLAG_IN_USE)) {
>           error_setg(errp, "Bitmap '%s' is in use", bm->name);
>           goto fail;
>       }
> @@ -974,23 +974,21 @@ bool qcow2_load_dirty_bitmaps(BlockDriverState *bs, Error 
> **errp)
>       }
>   
>       QSIMPLEQ_FOREACH(bm, bm_list, entry) {
> -        if (!(bm->flags & BME_FLAG_IN_USE)) {
> -            BdrvDirtyBitmap *bitmap = load_bitmap(bs, bm, errp);
> -            if (bitmap == NULL) {
> -                goto fail;
> -            }
> -            bm->dirty_bitmap = bitmap;
> +        BdrvDirtyBitmap *bitmap = load_bitmap(bs, bm, errp);
> +        if (bitmap == NULL) {
> +            goto fail;
> +        }
> +        bm->dirty_bitmap = bitmap;
>   
> -            if (!(bm->flags & BME_FLAG_AUTO)) {
> -                bdrv_disable_dirty_bitmap(bitmap);
> -            }
> -            bdrv_dirty_bitmap_set_persistance(bitmap, true);
> -            if (can_write(bs)) {
> -                bm->flags |= BME_FLAG_IN_USE;
> -                needs_update = true;
> -            } else {
> -                bdrv_dirty_bitmap_set_readonly(bitmap, true);
> -            }
> +        if (!(bm->flags & BME_FLAG_AUTO)) {
> +            bdrv_disable_dirty_bitmap(bitmap);
> +        }
> +        bdrv_dirty_bitmap_set_persistance(bitmap, true);
> +        if (can_write(bs)) {
> +            bm->flags |= BME_FLAG_IN_USE;
> +            needs_update = true;
> +        } else {
> +            bdrv_dirty_bitmap_set_readonly(bitmap, true);
>           }
>       }
>   


--
Best regards,
Vladimir