Re: [PATCHv2 net-next 2/3] bonding: use correct return value

Simon Horman [off-list ref] writes:

On Fri, Oct 18, 2024 at 12:46:18AM +0000, Hangbin Liu wrote:

quoted

On Thu, Oct 17, 2024 at 04:47:19PM +0200, Toke Høiland-Jørgensen wrote:

quoted

quoted

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index f0f76b6ac8be..6887a867fe8b 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c

@@ -5699,7 +5699,7 @@ static int bond_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 		if (dev_xdp_prog_count(slave_dev) > 0) {
 			SLAVE_NL_ERR(dev, slave_dev, extack,
 				     "Slave has XDP program loaded, please unload before enslaving");
-			err = -EOPNOTSUPP;
+			err = -EEXIST;

Hmm, this has been UAPI since kernel 5.15, so can we really change it
now? What's the purpose of changing it, anyway?

I just think it should return EXIST when the error is "Slave has XDP program
loaded". No special reason. If all others think we should not change it, I
can drop this patch.

Hi Toke,

Could you add some colour to what extent user's might rely on this error code?

Basically I think that if they do then we shouldn't change this.

Well, that's the trouble with UAPI, we don't really know. In libxdp and
xdp-tools we look at the return code to provide a nicer error message,
like:

https://github.com/xdp-project/xdp-tools/blob/master/lib/libxdp/libxdp.c#L615

and as a signal to fall back to loading the programme without a dispatcher:

https://github.com/xdp-project/xdp-tools/blob/master/lib/libxdp/libxdp.c#L1824

Both of these cases would be unaffected (or even improved) by this
patch, so in that sense I don't have a concrete objection, just a
general "userspace may react to this". In other words, my concern is
more of a general "we don't know, so this seems risky". If any of you
have more information about how bonding XDP is generally used, that may
help get a better idea of this?

-Toke