Re: [PATCH v10 5/9] copy-on-read: limit guest COR activity to base in COR driver

[Andrey Shinkevich]

On 05.10.2020 17:58, Vladimir Sementsov-Ogievskiy wrote:
> 29.09.2020 15:38, Andrey Shinkevich wrote:
> > Limit the guest's COR operations by the base node in the backing chain
> > when the base node name is given. It will be useful for a block stream
> > job when the COR-filter is applied.
> >
> > Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> > ---
> >   block/copy-on-read.c | 38 ++++++++++++++++++++++++++++++++++++--
> >   1 file changed, 36 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/copy-on-read.c b/block/copy-on-read.c
> > index e04092f..f53f7e0 100644
> > --- a/block/copy-on-read.c
> > +++ b/block/copy-on-read.c
> > @@ -121,8 +121,42 @@ static int coroutine_fn 
> > cor_co_preadv_part(BlockDriverState *bs,
> >                                              size_t qiov_offset,
> >                                              int flags)
> >   {
> > -    return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, 
> > qiov_offset,
> > -                               flags | BDRV_REQ_COPY_ON_READ);
> > +    int64_t n = 0;
> > +    int64_t size = offset + bytes;
> > +    int local_flags;
> > +    int ret;
> > +    BDRVStateCOR *state = bs->opaque;
> > +
> > +    if (!state->base_bs) {
> > +        return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, 
> > qiov_offset,
> > +                                   flags | BDRV_REQ_COPY_ON_READ);
> > +    }
> > +
> > +    while (offset < size) {
> > +        local_flags = flags;
> > +
> > +        /* In case of failure, try to copy-on-read anyway */
>
> But you add the flag only in case of success.. On any failure of furhter 
> is*allocated calls we should set the flag.

Yes, thanks.
Andrey

> > +        ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
> > +        if (!ret) {
> > +            ret = bdrv_is_allocated_above(bdrv_cow_bs(bs->file->bs),
> > +                                          state->base_bs, false, 
> > offset, n, &n);
> > +            if (ret > 0) {
> > +                local_flags |= BDRV_REQ_COPY_ON_READ;
> > +            }
> > +        }
> > +
> > +        ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, 
> > qiov_offset,
> > +                                  local_flags);
> > +        if (ret < 0) {
> > +            return ret;
> > +        }
> > +
> > +        offset += n;
> > +        qiov_offset += n;
> > +        bytes -= n;
> > +    }
> > +
> > +    return 0;
> >   }