Map key size mismatch when using xdp-loader.

[stevelorenz]

Dear developers of xdp-tools,

Thanks so much for your great effort! I am a PhD student and want to implement something using XDP. Therefore, I successfully set up the development environment using xdp-tool and started to follow xdp-tutorial. I mainly want to use the xdp-loader provided by xdp-tool to make loading/unloading stuff easier. When tried basic04 in xdp-tutorial, the xdp-loader does not work properly in pinning the map.

I run following command to load the XDP program on lo interface with a given pin path. It works fine without error (I have checked with xdp-loader status).

xdp-loader load -m skb -p /sys/fs/bpf lo ./xdp_prog_kern.o

Then I can see the map file in /sys/fs/bpf/programs/lo/xdp_pass. Then I modified the xdp-stats.c to use /sys/fs/bpf/programs as pin_dir and xdp_pass as the map name. Then I recompile the xdp_stats and run it with following command:

./xdp_stats --dev lo

It shows the following error:

ERR: check_map_fd_info() Map key size(-677305523) mismatch expected size(4)
ERR: map via FD not compatible 

So the user space program can find the map file but the key size is wrong when calling check_map_fd_info. This example works fine when I use the xdp_loader.c instead of the xdp-loader utility provided by the xdp-tools(xdp_loader.c pins the maps in /sys/fs/bpf/lo/xdp_stats_map).

Am I doing something wrong here? Could you please give me some hints? Thanks so much for your help.

• xdp-tool version: release: 0.0.3
• xdp-tutorial version: master:b13cfb8e6bef6c85017bb1ffdf6f2922a87fdb21

[tohojo]

Yeah, xdp-tools assumes somewhat newer versions of most of the BPF infrastructure than the tutorial currently does, so these two are not quite compatible, I'm afraid. The map pinning issue just came up over on xdp-tutorial, actually; see xdp-project/xdp-tutorial#125

[stevelorenz]

Thanks so much for your response. 😄 I didn't know about this issue. So I will now firstly finish the tutorial using the infrastructure provided in xdp-tutorial. And look at xdp-tools's implementation when I finish the tutorial (So after becoming a XDP advanced newbie 😉 ).

[tohojo]

Zuo Xiang <[email protected]> writes:

Thanks so much for your response. 😄 I didn't know about this issue. So I will now firstly finish the tutorial using the infrastructure provided in xdp-tutorial. And look at xdp-tools's implementation when I finish the tutorial (So after becoming a XDP advanced newbie 😉 ).

Sounds like a plan :)