Re: [bug report] vdpa_sim_blk: implement ramdisk behaviour

[Dan Carpenter <dan.carpenter@oracle.com>]

On Wed, Sep 29, 2021 at 02:07:12PM +0200, Stefano Garzarella wrote:
> On Wed, Sep 29, 2021 at 02:46:52PM +0300, Dan Carpenter wrote:
> > On Wed, Sep 29, 2021 at 02:37:42PM +0300, Dan Carpenter wrote:
> > >     89         /* The last byte is the status and we checked if the last iov has
> > >     90          * enough room for it.
> > >     91          */
> > >     92         to_push = vringh_kiov_length(&vq->in_iov) - 1;
> > > 
> > > Are you positive that vringh_kiov_length() cannot be zero?  I looked at
> > > the range_check() and there is no check for "if (*len == 0)".
> > > 
> > >     93
> > >     94         to_pull = vringh_kiov_length(&vq->out_iov);
> > >     95
> > >     96         bytes = vringh_iov_pull_iotlb(&vq->vring, &vq->out_iov, &hdr,
> > >     97                                       sizeof(hdr));
> > >     98         if (bytes != sizeof(hdr)) {
> > >     99                 dev_err(&vdpasim->vdpa.dev, "request out header too short\n");
> > >     100                 return false;
> > >     101         }
> > >     102
> > >     103         to_pull -= bytes;
> > > 
> > > The same "bytes" is used for both to_pull and to_push.  In this
> > > assignment it would only be used for the default case which prints an
> > > error message.
> > > 
> > 
> > Sorry, no.  This part is wrong.  "bytes" is not used for "to_push"
> > either here or below.  But I still am not sure "*len == 0" or how we
> 
> At line 84 we check that the last `in_iov` has at least one byte, so
> vringh_kiov_length(&vq->in_iov) cannot be zero.
> It will return the sum of all lengths, so at least 1.
> 
> Maybe better to add a comment.
> 
> > know that "to_push >= VIRTIO_BLK_ID_BYTES".
> 
> vringh_iov_push_iotlb() will push at least the bytes available in `in_iov`,
> if these are less, it will copy less bytes of VIRTIO_BLK_ID_BYTES.
> 
> Maybe here it would be better to add a check because the driver isn't
> following the specification.
> 
> And I'd avoid the subtraction highlighted by Smatch static checker.
> 
> Thanks for reporting. I'll send patches to fix these issues.

Nothing to fix, really.  I've looked at what you've explained and it's
all true so the code is fine as-is.  Thanks so much.

regards,
dan carpenter

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