Re: [PATCH bpf-next v2 1/2] net: xdp: refactor XDP_QUERY_PROG{,_HW} to netdev

On Sat, 1 Jun 2019 at 21:57, Jakub Kicinski
[off-list ref] wrote:

On Fri, 31 May 2019 19:18:17 +0000, Saeed Mahameed wrote:

quoted

quoted

+   if (!bpf_op || flags & XDP_FLAGS_SKB_MODE)
+           mode = XDP_FLAGS_SKB_MODE;
+
+   curr_mode = dev_xdp_current_mode(dev);
+
+   if (!offload && curr_mode && (mode ^ curr_mode) &
+       (XDP_FLAGS_DRV_MODE | XDP_FLAGS_SKB_MODE)) {

if i am reading this correctly this is equivalent to :

if (!offload && (curre_mode != mode))
offlad is false then curr_mode and mode must be DRV or GENERIC ..

Naw, if curr_mode is not set, i.e. nothing installed now, we don't care
about the diff.

quoted

better if you keep bitwise operations for actual bitmasks, mode and
curr_mode are not bitmask, they can hold one value each .. according to
your logic..

Well, they hold one bit each, whether one bit is a bitmap perhaps is
disputable? :)

I think the logic is fine.

Hmm, but changing to:

       if (!offload && curr_mode && mode != curr_mode)

is equal, and to Saeed's point, clearer. I'll go that route in a v3.

What happened to my request to move the change in behaviour for
disabling to a separate patch, tho, Bjorn? :)

Actually, I left that out completely. This patch doesn't change the
behavior. After I realized how the flags *should* be used, I don't
think my v1 change makes sense anymore. My v1 patch was to give an
error if you tried to disable, say generic if drv was enabled via
"auto detect/no flags". But this is catched by looking at the flags.

What I did, however, was moving the flags check into change_fd so that
the driver doesn't have to do the check. E.g. the Intel drivers didn't
do correct checking of flags.