Re: [PATCH][next] RDMA/cm: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

On 3/25/24 16:47, Jason Gunthorpe wrote:
> On Mon, Mar 25, 2024 at 02:24:07PM -0600, Gustavo A. R. Silva wrote:
> > -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
> > ready to enable it globally.
> >
> > Use the `struct_group_tagged()` helper to separate the flexible array
> > from the rest of the members in flexible `struct cm_work`, and avoid
> > embedding the flexible-array member in `struct cm_timewait_info`.
> >
> > Also, use `container_of()` to retrieve a pointer to the flexible
> > structure.
> >
> > So, with these changes, fix the following warning:
> > drivers/infiniband/core/cm.c:196:24: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > ---
> >   drivers/infiniband/core/cm.c | 21 ++++++++++++---------
> >   1 file changed, 12 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
> > index bf0df6ee4f78..80c87085499c 100644
> > --- a/drivers/infiniband/core/cm.c
> > +++ b/drivers/infiniband/core/cm.c
> > @@ -182,18 +182,21 @@ struct cm_av {
> >   };
> >   
> >   struct cm_work {
> > -	struct delayed_work work;
> > -	struct list_head list;
> > -	struct cm_port *port;
> > -	struct ib_mad_recv_wc *mad_recv_wc;	/* Received MADs */
> > -	__be32 local_id;			/* Established / timewait */
> > -	__be32 remote_id;
> > -	struct ib_cm_event cm_event;
> > +	/* New members must be added within the struct_group() macro below. */
> > +	struct_group_tagged(cm_work_hdr, hdr,
> > +		struct delayed_work work;
> > +		struct list_head list;
> > +		struct cm_port *port;
> > +		struct ib_mad_recv_wc *mad_recv_wc;	/* Received MADs */
> > +		__be32 local_id;			/* Established / timewait */
> > +		__be32 remote_id;
> > +		struct ib_cm_event cm_event;
> > +	);
> >   	struct sa_path_rec path[];
> >   };
>
> I didn't look, but does it make more sense to break out the path side
> into its own type and avoid the struct_group_tagged? I seem to
> remember only one thing used it.

I thought about that, but I'd have to change the parameter type of
`static int cm_timewait_handler(struct cm_work *work)`, and that would
imply also modifying the internals of function `cm_work_handler()` (and
then I didn't look much into it). So, the `struct_group_tagged()`
strategy is in general more cleaner and straightforward.

--
Gustavo