Re: [Qemu-devel] [PATCH v2] virtio-blk: set correct config size for the host driver

[Liu, Changpeng]

> -----Original Message-----
> From: Michael S. Tsirkin [mailto:address@hidden
> Sent: Tuesday, February 12, 2019 9:49 PM
> To: Liu, Changpeng <address@hidden>
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden
> Subject: Re: [PATCH v2] virtio-blk: set correct config size for the host 
> driver
> 
> On Tue, Feb 12, 2019 at 02:01:44PM +0800, Changpeng Liu wrote:
> > Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features support"
> > introduced extra fields to existing struct virtio_blk_config, when
> > migration was executed from older QEMU version to current head, it
> > will break the migration.  While here, set the correct config size
> > when initializing the host driver, for now, discard/write zeroes
> > are not supported by virtio-blk host driver, so set the config
> > size as before, users can change config size when adding the new
> > feature bits support.
> >
> > Signed-off-by: Changpeng Liu <address@hidden>
> 
> 
> Pls rewrite commit log as suggested in this thread
> and repost.
Thanks, repost a v3 patch to address the commit message and your following 
comments.
> 
> > ---
> >  hw/block/virtio-blk.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > index 9a87b3b..846b7b9 100644
> > --- a/hw/block/virtio-blk.c
> > +++ b/hw/block/virtio-blk.c
> > @@ -28,6 +28,9 @@
> >  #include "hw/virtio/virtio-bus.h"
> >  #include "hw/virtio/virtio-access.h"
> >
> > +#define VIRTIO_BLK_CFG_SIZE (offsetof(struct virtio_blk_config, num_queues)
> + \
> > +                             sizeof_field(struct virtio_blk_config, 
> > num_queues))
> > +
> 
> I would just do offsetof(max_discard_sectors)
> with a comment "we don't support discard yet, hide associated config
> fields".
> 
> >  static void virtio_blk_init_request(VirtIOBlock *s, VirtQueue *vq,
> >                                      VirtIOBlockReq *req)
> >  {
> > @@ -761,7 +764,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev,
> uint8_t *config)
> >      blkcfg.alignment_offset = 0;
> >      blkcfg.wce = blk_enable_write_cache(s->blk);
> >      virtio_stw_p(vdev, &blkcfg.num_queues, s->conf.num_queues);
> > -    memcpy(config, &blkcfg, sizeof(struct virtio_blk_config));
> > +    memcpy(config, &blkcfg, VIRTIO_BLK_CFG_SIZE);
> 
> 
> Let's add QEMU_BUILD_BUG_ON(VIRTIO_BLK_CFG_SIZE <= sizeof(struct
> virtio_blk_config)) just for documentation purposes.
> 
> >  }
> >
> >  static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t 
> > *config)
> > @@ -769,7 +772,7 @@ static void virtio_blk_set_config(VirtIODevice *vdev,
> const uint8_t *config)
> >      VirtIOBlock *s = VIRTIO_BLK(vdev);
> >      struct virtio_blk_config blkcfg;
> >
> > -    memcpy(&blkcfg, config, sizeof(blkcfg));
> > +    memcpy(&blkcfg, config, VIRTIO_BLK_CFG_SIZE);
> 
> 
> Here too, QEMU_BUILD_BUG_ON(VIRTIO_BLK_CFG_SIZE <= sizeof(blkcfg))
> 
> >
> >      aio_context_acquire(blk_get_aio_context(s->blk));
> >      blk_set_enable_write_cache(s->blk, blkcfg.wce != 0);
> > @@ -952,8 +955,7 @@ static void virtio_blk_device_realize(DeviceState *dev,
> Error **errp)
> >          return;
> >      }
> >
> > -    virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK,
> > -                sizeof(struct virtio_blk_config));
> > +    virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, VIRTIO_BLK_CFG_SIZE);
> >
> >      s->blk = conf->conf.blk;
> >      s->rq = NULL;
> > --
> > 1.9.3