Re: [Qemu-block] [Qemu-devel] [PATCH v20 13/30] block: new bdrv_reopen_bitmaps_rw interface

[Sementsov-Ogievskiy Vladimir]

On 03.06.2017 01:17, John Snow wrote:
> On 06/02/2017 07:21 AM, Vladimir Sementsov-Ogievskiy wrote:
> > Add format driver handler, which should mark loaded read-only
> > bitmaps as 'IN_USE' in the image and unset read_only field in
> > corresponding BdrvDirtyBitmap's.
> >
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> > ---
> >   block.c                   | 17 +++++++++++++++++
> >   include/block/block_int.h |  7 +++++++
> >   2 files changed, 24 insertions(+)
> >
> > diff --git a/block.c b/block.c
> > index 04af7697dc..161db9e32a 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -2946,12 +2946,16 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
> >   {
> >       BlockDriver *drv;
> >       BlockDriverState *bs;
> > +    bool old_can_write, new_can_write;
> >   
> >       assert(reopen_state != NULL);
> >       bs = reopen_state->bs;
> >       drv = bs->drv;
> >       assert(drv != NULL);
> >   
> > +    old_can_write =
> > +        !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) & BDRV_O_INACTIVE);
> > +
> >       /* If there are any driver level actions to take */
> >       if (drv->bdrv_reopen_commit) {
> >           drv->bdrv_reopen_commit(reopen_state);
> > @@ -2965,6 +2969,19 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
> >       bs->read_only = !(reopen_state->flags & BDRV_O_RDWR);
> >   
> >       bdrv_refresh_limits(bs, NULL);
> > +
> > +    new_can_write =
> > +        !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) & BDRV_O_INACTIVE);
> > +    if (!old_can_write && new_can_write && drv->bdrv_reopen_bitmaps_rw) {
> > +        Error *local_err = NULL;
> > +        if (drv->bdrv_reopen_bitmaps_rw(bs, &local_err) < 0) {
> > +            /* This is not fatal, bitmaps just left read-only, so all following
> > +             * writes will fail. User can remove read-only bitmaps to unblock
> > +             * writes.
> > +             */
> > +            error_report_err(local_err);
> > +        }
> > +    }
> >   }
> >   
> >   /*
> > diff --git a/include/block/block_int.h b/include/block/block_int.h
> > index 8d3724cce6..1dc6f2e90d 100644
> > --- a/include/block/block_int.h
> > +++ b/include/block/block_int.h
> > @@ -380,6 +380,13 @@ struct BlockDriver {
> >                                uint64_t parent_perm, uint64_t parent_shared,
> >                                uint64_t *nperm, uint64_t *nshared);
> >   
> > +    /**
> > +     * Bitmaps should be marked as 'IN_USE' in the image on reopening image
> > +     * as rw. This handler should realize it. It also should unset readonly
> > +     * field of BlockDirtyBitmap's in case of success.
> > +     */
> > +    int (*bdrv_reopen_bitmaps_rw)(BlockDriverState *bs, Error **errp);
> > +
> Hmm, do we need a new top-level hook for this? We already have
> .bdrv_reopen_commit and .bdrv_reopen_prepare which inform the
> blockdriver that a reopen event is occurring.
>
> Can't we just amend qcow2_reopen_prepare and qcow2_reopen_commit to do
> the necessary tasks of either:
>
> (A) Flushing the bitmap in preparation for reopening as RO, or
> (B) Writing in_use and removing the RO flag in preparation for reopening
> as RW

(A) is done (see patch about reopen RO)

(B) - We can't do it, as on this preparation the image is still RO, and 
I've created new handler, write 'in_use' _after_ the point when new 
flags was set.

> >       QLIST_ENTRY(BlockDriver) list;
> >   };
> >   
>
> Well, design issues aside, I will at least confirm that I think this
> patch should work as designed, and I will leave the design critiques to
> Max and Kevin:
>
> Reviewed-by: John Snow <address@hidden>

--
Best regards,
Vladimir.