Re: [Qemu-devel] [PATCH 8/9] block: Introduce BlockDriver.bdrv_drain callback

[Fam Zheng <famz@redhat.com>]

On Wed, 10/28 11:13, Kevin Wolf wrote:
> Am 26.10.2015 um 07:24 hat Fam Zheng geschrieben:
> > Drivers can have internal request sources that generate IO, like the
> > need_check_timer in QED. Since we want quiesced periods that contain
> > nested event loops in block layer, we need to have a way to disable such
> > event sources.
> > 
> > Block drivers must implement the "bdrv_drain" callback if it has any
> > internal sources that can generate I/O activity, like a timer or a
> > worker thread (even in a library) that can schedule QEMUBH in an
> > asynchronous callback.
> > 
> > Update the comments of bdrv_drain and bdrv_drained_begin accordingly.
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > Reviewed-by: Jeff Cody <jcody@redhat.com>
> > Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  block/io.c                | 6 +++++-
> >  include/block/block_int.h | 6 ++++++
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/block/io.c b/block/io.c
> > index 358c3c4..a740827 100644
> > --- a/block/io.c
> > +++ b/block/io.c
> > @@ -234,7 +234,8 @@ bool bdrv_requests_pending(BlockDriverState *bs)
> >  }
> >  
> >  /*
> > - * Wait for pending requests to complete on a single BlockDriverState subtree
> > + * Wait for pending requests to complete on a single BlockDriverState subtree,
> > + * and suspend block driver's internal I/O until next request arrives.
> >   *
> >   * Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState
> >   * AioContext.
> > @@ -247,6 +248,9 @@ void bdrv_drain(BlockDriverState *bs)
> >  {
> >      bool busy = true;
> >  
> > +    if (bs->drv && bs->drv->bdrv_drain) {
> > +        bs->drv->bdrv_drain(bs);
> > +    }
> 
> Does this need to be recursive? Recursing into bs->file and bs->backing
> would be consistent with the current bdrv_requests_pending(); but I'm
> planning to send a patch to extend this to all children.
> 

Yes, I'll change it to recurse into all children.

Fam