Re: [PATCH 3/7] tcp_conn: Avoid 7-bit hole in struct tcp_splice_conn

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 29 Jan 2025 12:02:09 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Tue, Jan 28, 2025 at 07:48:33AM +0100, Stefano Brivio wrote:
> > On Tue, 28 Jan 2025 11:53:09 +1100
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > On Tue, Jan 28, 2025 at 12:15:28AM +0100, Stefano Brivio wrote:  
> > > > Moving in_epoll out of the common flow data created a 7-bit hole in
> > > > struct tcp_splice_conn: repack by shrinking @flags by one (otherwise
> > > > unused) bit.    
> > > 
> > > Is this actually necessary for the migration stuff?  Or just a cleanup
> > > you spotted along the way?  
> > 
> > I thought it was helpful to keep the same size on 32-bit, but it looks
> > like it's not actually needed.
> > 
> > Let me drop it from this series as it's just noise and I'm trying to
> > keep this slim. If we are all happy with it I can apply it. If not I'll
> > forget about it.  
> 
> Eh, I don't care that much either way.
> 
> Note, btw, that bit-field packing is another way source and
> destination could potentially have mismatching data structures.  IIUC
> bit field packing is described by the ABI and doesn't necessarily
> match the byte endianness.

Right, that's actually the reason that brought me to this change: I was
comparing stuff between x86_64 and armv6l. On the other hand, this part
of the specific ABI is generally considered stable so I can rely on it.

-- 
Stefano