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xdp-project / xdp-tools

Utilities and example programs for use with XDP

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xdp-loader not finding xdp_dispatcher by default

hhoffstaette opened this issue · comments

commented

I apologize for the barrage of bug reports, but that's just what I do 🤡

My first steps with XDP are all about trying to load a simple packet dropper based on the Ethernet frame type. As first step I used ip to load it, and it works fine: the frames are dropped correctly. \o/

Now with xdp-tools installed, xdp-loader shows that the program is indeed loaded:

$ip link set dev eth0 xdp obj /usr/local/lib/bpf/homeplug_av_drop.o sec .text
$xdp-loader status eth0                                                      
CURRENT XDP PROGRAM STATUS:

Interface        Prio  Program name      Mode     ID   Tag               Chain actions
--------------------------------------------------------------------------------------
eth0                                     skb      125  fbd415544de357c1

I can also unload the program:

$xdp-loader unload eth0 -i 125                                               
$xdp-loader status eth0
CURRENT XDP PROGRAM STATUS:

Interface        Prio  Program name      Mode     ID   Tag               Chain actions
--------------------------------------------------------------------------------------
eth0                   <No XDP program loaded!>

So basically the tools work.

Now I want to use the loader to actually load. I understand that it wants to use an xdp_dispatcher for loading/handling multiple programs, but something is not right:

xdp-loader load eth0 /usr/local/lib/bpf/homeplug_av_drop.o 
 libxdp: Couldn't find a BPF file with name xdp-dispatcher.o
 libxdp: Couldn't open BPF file xdp-dispatcher.o
Couldn't attach XDP program on iface 'eth0': No such file or directory(-2)

Let's see with -vv:

xdp-loader load -vv eth0 /usr/local/lib/bpf/homeplug_av_drop.o
Current rlimit 8388608 already >= minimum 1048576
Loading 1 files on interface 'eth0'.
  libbpf: loading /usr/local/lib/bpf/homeplug_av_drop.o
  libbpf: elf: section(2) .text, size 136, link 0, flags 6, type=1
  libbpf: sec '.text': found program 'dropper' at insn offset 0 (0 bytes), code size 17 insns (136 bytes)
  libbpf: elf: section(3) license, size 4, link 0, flags 3, type=1
  libbpf: license of /usr/local/lib/bpf/homeplug_av_drop.o is GPL
  libbpf: elf: section(13) .BTF, size 778, link 0, flags 0, type=1
  libbpf: elf: section(15) .BTF.ext, size 192, link 0, flags 0, type=1
  libbpf: elf: section(23) .symtab, size 360, link 1, flags 0, type=2
  libbpf: looking for externs among 15 symbols...
  libbpf: collected 0 externs total
  libbpf: prog 'dropper': unrecognized ELF section name '.text'
 libxdp: DATASEC '.xdp_run_config' not found.
XDP program 0: Run prio: 50. Chain call actions: XDP_PASS
 libxdp: Generating multi-prog dispatcher for 1 programs
 libxdp: Checking for kernel frags support
 libxdp: Looking for '/usr/local/lib/bpf/xdp-dispatcher.o'
 libxdp: Couldn't find a BPF file with name xdp-dispatcher.o
 libxdp: Couldn't open BPF file xdp-dispatcher.o
Couldn't attach XDP program on iface 'eth0': No such file or directory(-2)

Why would it want to load the dispatcher from my private directory?
I can see that the dispatcher is installed:

$locate xdp-dispatcher
/usr/lib/bpf/xdp-dispatcher.o

So I copy it into the expected directory and try again:

xdp-loader load -v eth0 /usr/local/lib/bpf/homeplug_av_drop.o 
Current rlimit 8388608 already >= minimum 1048576
Loading 1 files on interface 'eth0'.
XDP program 0: Run prio: 50. Chain call actions: XDP_PASS
 libxdp: Error attaching XDP program to ifindex 2: Operation not supported
 libxdp: XDP mode not supported; try using SKB mode
Attaching XDP program in native mode not supported - try SKB mode.

Looks like my laptop NIC is too cheap and ip used skb mode automatically, so..

xdp-loader load -v -m skb eth0 /usr/local/lib/bpf/homeplug_av_drop.o
Current rlimit 8388608 already >= minimum 1048576
Loading 1 files on interface 'eth0'.
XDP program 0: Run prio: 50. Chain call actions: XDP_PASS
root>xdp-loader status eth0                                              
CURRENT XDP PROGRAM STATUS:

Interface        Prio  Program name      Mode     ID   Tag               Chain actions
--------------------------------------------------------------------------------------
eth0                   xdp_dispatcher    skb      173  90f686eb86991928 
 =>              50     dropper                   182  fbd415544de357c1  XDP_PASS

🎉

So while I could get it to work, I'm confused - is this some kind of misconfiguration or a bug?

commented

Obviously I find a hint right after sending..
In lib/defines.mk I see:

PREFIX?=/usr/local
LIBDIR?=$(PREFIX)/lib
BPF_OBJECT_DIR ?=$(LIBDIR)/bpf

and while we override PREFIX for installation, we apparently don't override it for building - successfully compiling the wrong search path into libxdp. This seems to be the problem.

commented

This is clearly a packaging problem in Gentoo, so closing this. Sorry for the long story.

commented