Re: [Qemu-devel] [PATCH v3] 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 11:11 PM
> To: Liu, Changpeng <address@hidden>
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden
> Subject: Re: [PATCH v3] virtio-blk: set correct config size for the host 
> driver
> 
> On Tue, Feb 12, 2019 at 11:19:49PM +0800, Changpeng Liu wrote:
> > Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features
> > support" added fields to struct virtio_blk_config. This changes
> > the size of the config space and breaks migration from QEMU 3.1
> > and older:
> >
> > qemu-system-ppc64: get_pci_config_device: Bad config data: i=0x10 read: 41
> device: 1 cmask: ff wmask: 80 w1cmask:0
> > qemu-system-ppc64: Failed to load PCIDevice:config
> > qemu-system-ppc64: Failed to load virtio-blk:virtio
> > qemu-system-ppc64: error while loading state for instance 0x0 of device
> 'address@hidden:01.0/virtio-blk'
> > qemu-system-ppc64: load of migration failed: Invalid argument
> >
> > Since virtio-blk doesn't support the "discard" and "write zeroes"
> > features, it shouldn't even expose the associated fields in the
> > config space actually. Just include all fields up to num_queues to
> > match QEMU 3.1 and older.
> >
> > Signed-off-by: Changpeng Liu <address@hidden>
> 
> OK almost.
> 
> > ---
> >  hw/block/virtio-blk.c | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > index 9a87b3b..0ff5315 100644
> > --- a/hw/block/virtio-blk.c
> > +++ b/hw/block/virtio-blk.c
> > @@ -28,6 +28,10 @@
> >  #include "hw/virtio/virtio-bus.h"
> >  #include "hw/virtio/virtio-access.h"
> >
> > +/* We don't support discard yet, hide associated config fields. */
> > +#define VIRTIO_BLK_CFG_SIZE offsetof(struct virtio_blk_config, \
> > +                                     max_discard_sectors)
> > +
> >  static void virtio_blk_init_request(VirtIOBlock *s, VirtQueue *vq,
> >                                      VirtIOBlockReq *req)
> >  {
> > @@ -761,7 +765,9 @@ 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);
> > +    QEMU_BUILD_BUG_ON(VIRTIO_BLK_CFG_SIZE > sizeof(struct
> virtio_blk_config));
> > +
> 
> Oh probably sizeof blkcfg here, right?
> Also we don't need the empty line here.
Ok, removed the empty line and use sizeof(blkcfg) instead with v4.
> 
> >  }
> >
> >  static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t 
> > *config)
> > @@ -769,7 +775,8 @@ 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);
> > +    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 +959,7 @@ 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