On Wed, Feb 15, 2023 at 11:09:36AM +0100, Jesper Dangaard Brouer wrote:
> With our XDP-hints kfunc approach, where individual drivers overload the
> default implementation, it can be hard for API users to determine
> whether or not the current device driver have this kfunc available.
>
> Change the default implementations to use an errno (ENODEV), that
> drivers shouldn't return, to make it possible for BPF runtime to
> determine if bpf kfunc for xdp metadata isn't implemented by driver.
I think it diverts ENODEV usage from its original purpose too much. Maybe
providing information in dmesg would be a better solution?
>
> This is intended to ease supporting and troubleshooting setups. E.g.
> when users on mailing list report -19 (ENODEV) as an error, then we can
> immediately tell them their kernel is too old.
Do you mean driver being too old, not kernel?
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> ---
> net/core/xdp.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 26483935b7a4..7bb5984ae4f7 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -722,10 +722,12 @@ __diag_ignore_all("-Wmissing-prototypes",
> * @timestamp: Return value pointer.
> *
> * Returns 0 on success or ``-errno`` on error.
> + *
> + * -ENODEV (19): means device driver doesn't implement kfunc
> */
> __bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
> {
> - return -EOPNOTSUPP;
> + return -ENODEV;
> }
>
> /**
> @@ -734,10 +736,12 @@ __bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *tim
> * @hash: Return value pointer.
> *
> * Returns 0 on success or ``-errno`` on error.
> + *
> + * -ENODEV (19): means device driver doesn't implement kfunc
> */
> __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash)
> {
> - return -EOPNOTSUPP;
> + return -ENODEV;
> }
>
> __diag_pop();
Documentation contains the following lines:
Not all kfuncs have to be implemented by the device driver; when not
implemented, the default ones that return ``-EOPNOTSUPP`` will be used.
If you decide to proceed with current implementation, you'd need to update them
in v2.
>
>
