Re: [PATCH] net: pad virtio_net_ff_cap_data

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 19, 2025 at 09:38:18AM +0000, Parav Pandit wrote:
> 
> 
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: 19 November 2025 02:04 PM
> > 
> > On Wed, Nov 19, 2025 at 08:29:48AM +0000, Parav Pandit wrote:
> > >
> > > > From: Michael S. Tsirkin <mst@redhat.com>
> > > > Sent: 19 November 2025 01:54 PM
> > > >
> > > > struct virtio_net_ff_cap_data has 4 byte fields but the size is not
> > > > a multiple of 4.  drivers can easily get it wrong since compilers
> > > > tend to add padding to align such structures.
> > > >
> > > > Since we are always allowed to pad or truncate admin commands, let's
> > > > do just that here.
> > > >
> > > > Fixes: 899bb0c ("virtio-net: Add flow filter capability")
> Prefer 12 letter tag.
> Not a must as we are about to release.
> So will change locally when I merge.

thanks


> > > > Cc: "Parav Pandit" <parav@nvidia.com>
> > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > > ---
> > > >  device-types/net/description.tex | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/device-types/net/description.tex b/device-
> > > > types/net/description.tex index 9833d16..0b4fcac 100644
> > > > --- a/device-types/net/description.tex
> > > > +++ b/device-types/net/description.tex
> > > > @@ -3055,6 +3055,7 @@ \subsubsection{Flow filter}\label{sec:Device
> > > > Types / Network Device / Device Ope
> > > >          le32 rules_per_group_limit;
> > > >          u8 last_rule_priority;
> > > >          u8 selectors_per_classifier_limit;
> > > > +        u8 reserved[2];
> > > >  };
> > > >  \end{lstlisting}
> > > >
> > > Thanks for the fix.
> > > We should align to the 8B boundary instead of 4B.
> > > It should be reserved[6].
> > 
> > 
> > I prefer the 4b one because it likely is what drivers have been doing anyway,
> > unknowingly.
> >
> Ok.
>  
> > > > @@ -3071,6 +3072,8 @@ \subsubsection{Flow filter}\label{sec:Device
> > > > Types / Network Device / Device Ope
> > > > \field{selectors_per_classifier_limit} is the maximum number of selectors
> > that a classifier can have.
> > > >
> > > > +\field{reserved} is reserved and set to zero.
> > > > +
> > > >  \subparagraph{VIRTIO_NET_FF_SELECTOR_CAP}
> > > >  \label{par:Device Types / Network Device / Device Operation / Flow
> > > > filter / Device and driver capabilities /
> > > > VIRTIO-NET-FF-SELECTOR-CAP}
> > > >
> > > > --
> > > > MST
> Reviewed-by: Parav Pandit <parav@nvidia.com>