Re: [Qemu-devel] [PATCH 1/2] iscsi: add support for bdrv_co_is_allocated()

[Stefan Hajnoczi]

On Fri, Jun 21, 2013 at 11:18:42AM +0200, Kevin Wolf wrote:
> Am 20.06.2013 um 20:20 hat Peter Lieven geschrieben:
> > @@ -800,6 +801,60 @@ iscsi_getlength(BlockDriverState *bs)
> >      return len;
> >  }
> >  
> > +static int coroutine_fn iscsi_co_is_allocated(BlockDriverState *bs,
> > +                                              int64_t sector_num,
> > +                                              int nb_sectors, int *pnum)
> > +{
> > +    IscsiLun *iscsilun = bs->opaque;
> > +    struct scsi_task *task = NULL;
> > +    struct scsi_get_lba_status *lbas = NULL;
> > +    struct scsi_lba_status_descriptor *lbasd = NULL;
> > +    int ret;
> > +
> > +    *pnum = nb_sectors;
> > +
> > +    if (iscsilun->lbpme == 0) {
> > +        return 1;
> > +    }
> > +
> > +    /* in-flight requests could invalidate the lba status result */
> > +    while (iscsi_process_flush(iscsilun)) {
> > +        qemu_aio_wait();
> > +    }
> 
> Note that you're blocking here. The preferred way would be something
> involving a yield from the coroutine and a reenter as soon as all
> requests are done. Maybe a CoRwLock does what you need?

The other option is to avoid synchronization here and instead process
bs->tracked_requests so that any in-flight writes count as allocated.

Stefan