Re: [Qemu-devel] [PATCH 1/3] block: Additional info string in ImageInfo and BDI

[Max Reitz]

On 2013-09-18 16:59, Stefan Hajnoczi wrote:
> On Thu, Sep 05, 2013 at 02:05:13PM +0200, Max Reitz wrote:
> > diff --git a/block.c b/block.c
> > index 26639e8..9fd9f3a 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -1921,7 +1921,7 @@ void bdrv_round_to_clusters(BlockDriverState *bs,
> >                               int64_t *cluster_sector_num,
> >                               int *cluster_nb_sectors)
> >   {
> > -    BlockDriverInfo bdi;
> > +    BlockDriverInfo bdi = { .info_string = NULL };
> >   
> >       if (bdrv_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) {
> >           *cluster_sector_num = sector_num;
> > @@ -1932,6 +1932,7 @@ void bdrv_round_to_clusters(BlockDriverState *bs,
> >           *cluster_nb_sectors = QEMU_ALIGN_UP(sector_num - *cluster_sector_num +
> >                                               nb_sectors, c);
> >       }
> > +    g_free(bdi.info_string);
> >   }
> This function is called in the I/O path.  It's not appropriate to
> generate an options string each time this gets called :).
>
> Together with Eric's comments it seems like this change needs a
> different interface that is QMP-friendly and not in the I/O path.
>
> Stefan
I've already sent a v2, v3 and v4 which address Eric's comment. However, 
your problem still remains. I think I might either add a new function 
for specifically requesting the format specific information (instead of 
generally including it in BDI) or introduce a flag parameter for 
bdrv_get_info which requests that BDI field to be filled (or, more 
generally, which will prevent bdrv_get_info from performing any 
relatively expensive operation).

Max