bpf/tests/scapy: show pkt diffs on assertion failures and improve outputs #41124

msune · 2025-08-13T14:08:50Z

This small patchset improves:

trace_diff_pkts.py by:
- Showing the diff between the expected packet and the one received, (potentially) field by field. This is done
  after dumping both packets.
- Print pkt lengths in bytes as part of dumping the packets.
- Changes formatting to make it easier to read.
ASSERT_CTX_BUF_OFF by:
- Unconditionally dumping packets, even when lengths mismatch.
- Adds useful info in the assert message (e.g. sizes).

Before this patch series

Example of CTX len < LEN

time=2025-08-13T16:02:22.755411559+02:00 level=info msg="Initializing dissection cache..."
--- FAIL: TestBPF (14.12s)
    --- FAIL: TestBPF/tc_l2_announcement.o (0.07s)
        --- FAIL: TestBPF/tc_l2_announcement.o/1_happy_path (0.00s)
            bpf_test.go:457: tc_l2_announcement.c:150: CTX size - offset < LEN tc_l2_announcement.c:150
        bpf_test.go:62: -> 1: [error]
FAIL
FAIL	github.com/cilium/cilium/bpf/tests/bpftest	14.144s
FAIL

Example of buffer length < LEN:

--- FAIL: TestBPF (14.51s)
    --- FAIL: TestBPF/tc_l2_announcement.o (0.08s)
        --- FAIL: TestBPF/tc_l2_announcement.o/1_happy_path (0.00s)
            bpf_test.go:457: tc_l2_announcement.c:150: CTX and buffer 'EXPECTED_ARP_REP' mismatch tc_l2_announcement.c:150
        bpf_test.go:62: -> 1: [error]
FAIL
FAIL	github.com/cilium/cilium/bpf/tests/bpftest	14.533s
FAIL
=== Start tc_l2_announcement.c:150 'arp_rep_ok' ===
--- Expected ---
###[ Ethernet ]### 
  dst       = de:ad:be:ef:de:ef
  src       = 13:37:13:37:13:37
  type      = 0x9000

--- Got ---
###[ Ethernet ]### 
  dst       = de:ad:be:ef:de:ef
  src       = 13:37:13:37:13:37
  type      = ARP

===  End  tc_l2_announcement.c:150 'arp_rep_ok' ===

After:

Simple diff:

--- FAIL: TestBPF (15.31s)
    --- FAIL: TestBPF/tc_l2_announcement.o (0.07s)
        --- FAIL: TestBPF/tc_l2_announcement.o/1_happy_path (0.00s)
            bpf_test.go:457: tc_l2_announcement.c:150: CTX and buffer 'EXPECTED_ARP_REP' content mismatch 
        bpf_test.go:62: -> 1: [error]
FAIL
FAIL	github.com/cilium/cilium/bpf/tests/bpftest	15.344s
FAIL
=== START tc_l2_announcement.c:150 'arp_rep_ok' ===
>>> Expected (len: 42 bytes) <<<
###[ Ethernet ]### 
  dst       = de:ad:be:ef:de:ef
  src       = 31:41:59:26:35:89
  type      = ARP
###[ ARP ]### 
     hwtype    = Ethernet (10Mb)
     ptype     = IPv4
     hwlen     = 6
     plen      = 4
     op        = is-at
     hwsrc     = 13:37:13:37:13:37
     psrc      = 172.16.10.1
     hwdst     = de:ad:be:ef:de:ef
     pdst      = 0.0.0.53

>>> Got (len: 42 bytes) <<<
###[ Ethernet ]### 
  dst       = de:ad:be:ef:de:ef
  src       = 13:37:13:37:13:37
  type      = ARP
###[ ARP ]### 
     hwtype    = Ethernet (10Mb)
     ptype     = IPv4
     hwlen     = 6
     plen      = 4
     op        = is-at
     hwsrc     = 13:37:13:37:13:37
     psrc      = 172.16.10.1
     hwdst     = de:ad:be:ef:de:ef
     pdst      = 110.0.11.1

>>> Diff <<<
  --- a/pkt (Expected)
  +++ b/pkt (Got)

  - [ Ether ].src: 31:41:59:26:35:89
  + [ Ether ].src: 13:37:13:37:13:37
  - [ Ether ][ ARP ].pdst: 0.0.0.53
  + [ Ether ][ ARP ].pdst: 110.0.11.1

=== END tc_l2_announcement.c:150 'arp_rep_ok' ===

Example of CTX len < LEN

    --- FAIL: TestBPF (14.35s)
        --- FAIL: TestBPF/tc_l2_announcement.o (0.07s)
            --- FAIL: TestBPF/tc_l2_announcement.o/1_happy_path (0.00s)
                bpf_test.go:457: tc_l2_announcement.c:150: CTX len (46) - offset (4) < LEN (65)
            bpf_test.go:62: -> 1: [error]
    FAIL
    FAIL    github.com/cilium/cilium/bpf/tests/bpftest      14.372s
    FAIL
    === START tc_l2_announcement.c:150 'arp_rep_ok' ===
    >>> Expected (len: 65 bytes) <<<
      dst       = de:ad:be:ef:de:ef
      src       = 13:37:13:37:13:37
      type      = IPv4
         version   = 4
         ihl       = 5
         tos       = 0x0
         len       = 51
         id        = 1
         flags     =
         frag      = 0
         ttl       = 64
         proto     = tcp
         chksum    = 0x7cc2
         src       = 127.0.0.1
         dst       = 127.0.0.1
         \options   \
            sport     = ftp_data
            dport     = http
            seq       = 0
            ack       = 0
            dataofs   = 5
            reserved  = 0
            flags     = S
            window    = 8192
            chksum    = 0x1fa3
            urgptr    = 0
            options   = []
               load      = 'Hello world'
    
    >>> Got (len: 42 bytes) <<<
      dst       = de:ad:be:ef:de:ef
      src       = 13:37:13:37:13:37
      type      = ARP
         hwtype    = Ethernet (10Mb)
         ptype     = IPv4
         hwlen     = 6
         plen      = 4
         op        = is-at
         hwsrc     = 13:37:13:37:13:37
         psrc      = 172.16.10.1
         hwdst     = de:ad:be:ef:de:ef
         pdst      = 110.0.11.1
    
    >>> Diff <<<
      --- a/pkt (Expected)
      +++ b/pkt (Got)
    
      - [ Ether ].type: 2048
      + [ Ether ].type: 2054
      - [ Ether ][ IP ].options: []
      - [ Ether ][ IP ].version: 4
      - [ Ether ][ IP ].ihl: 5
      - [ Ether ][ IP ].tos: 0
      - [ Ether ][ IP ].len: 51
      - [ Ether ][ IP ].id: 1
      - [ Ether ][ IP ].flags:
      - [ Ether ][ IP ].frag: 0
      - [ Ether ][ IP ].ttl: 64
      - [ Ether ][ IP ].proto: 6
      - [ Ether ][ IP ].chksum: 31938
      - [ Ether ][ IP ].src: 127.0.0.1
      - [ Ether ][ IP ].dst: 127.0.0.1
      - [ Ether ][ IP ][ TCP ].sport: 20
      - [ Ether ][ IP ][ TCP ].dport: 80
      - [ Ether ][ IP ][ TCP ].seq: 0
      - [ Ether ][ IP ][ TCP ].ack: 0
      - [ Ether ][ IP ][ TCP ].dataofs: 5
      - [ Ether ][ IP ][ TCP ].reserved: 0
      - [ Ether ][ IP ][ TCP ].flags: S
      - [ Ether ][ IP ][ TCP ].window: 8192
      - [ Ether ][ IP ][ TCP ].chksum: 8099
      - [ Ether ][ IP ][ TCP ].urgptr: 0
      - [ Ether ][ IP ][ TCP ].options: []
      - [ Ether ][ IP ][ TCP ][ Raw ].load: b'Hello world'
      + [ Ether ][ ARP ].hwtype: 1
      + [ Ether ][ ARP ].ptype: 2048
      + [ Ether ][ ARP ].hwlen: 6
      + [ Ether ][ ARP ].plen: 4
      + [ Ether ][ ARP ].op: 2
      + [ Ether ][ ARP ].hwsrc: 13:37:13:37:13:37
      + [ Ether ][ ARP ].psrc: 172.16.10.1
      + [ Ether ][ ARP ].hwdst: de:ad:be:ef:de:ef
      + [ Ether ][ ARP ].pdst: 110.0.11.1
    
    === END tc_l2_announcement.c:150 'arp_rep_ok' ===

Example of buffer length < LEN:

    --- FAIL: TestBPF (14.42s)
        --- FAIL: TestBPF/tc_l2_announcement.o (0.07s)
            --- FAIL: TestBPF/tc_l2_announcement.o/1_happy_path (0.00s)
                bpf_test.go:457: tc_l2_announcement.c:151: Buffer 'EXPECTED_ARP_REP' of len (14) < LEN (42)
            bpf_test.go:62: -> 1: [error]
    FAIL
    FAIL    github.com/cilium/cilium/bpf/tests/bpftest      14.444s
    FAIL
    === START tc_l2_announcement.c:151 'arp_rep_ok' ===
    >>> Expected (len: 14 bytes) <<<
      dst       = de:ad:be:ef:de:ef
      src       = 13:37:13:37:13:37
      type      = 0x9000
    
    >>> Got (len: 42 bytes) <<<
      dst       = de:ad:be:ef:de:ef
      src       = 13:37:13:37:13:37
      type      = ARP
         hwtype    = Ethernet (10Mb)
         ptype     = IPv4
         hwlen     = 6
         plen      = 4
         op        = is-at
         hwsrc     = 13:37:13:37:13:37
         psrc      = 172.16.10.1
         hwdst     = de:ad:be:ef:de:ef
         pdst      = 110.0.11.1
    
    >>> Diff <<<
      --- a/pkt (Expected)
      +++ b/pkt (Got)
    
      - [ Ether ].type: 36864
      + [ Ether ].type: 2054
      + [ Ether ][ ARP ].hwtype: 1
      + [ Ether ][ ARP ].ptype: 2048
      + [ Ether ][ ARP ].hwlen: 6
      + [ Ether ][ ARP ].plen: 4
      + [ Ether ][ ARP ].op: 2
      + [ Ether ][ ARP ].hwsrc: 13:37:13:37:13:37
      + [ Ether ][ ARP ].psrc: 172.16.10.1
      + [ Ether ][ ARP ].hwdst: de:ad:be:ef:de:ef
      + [ Ether ][ ARP ].pdst: 110.0.11.1
    
    === END tc_l2_announcement.c:151 'arp_rep_ok' ===

msune · 2025-08-13T14:09:16Z

cc @smagnani96

This commit improves `trace_diff_pkts.py` by: * Showing the diff, (potentially) field by field. This is done _after_ the dump of the entire packet. * Print pkt lengths in bytes. * Changes formatting to make it easier to read. Signed-off-by: Marc Suñé <marc.sune@isovalent.com>

Prior to this commit, if packet lengths were mismatching, `ASSERT_CTX_BUF_OFF` was NOT attempting to dump the packet. This commit: * Modifies `ASSERT_CTX_BUF_OFF` logic so that packets are always dumped. * Adds useful info in the assert message (e.g. sizes). Signed-off-by: Marc Suñé <marc.sune@isovalent.com>

msune · 2025-08-15T08:10:44Z

/test

msune · 2025-08-15T08:11:29Z

(rebased to workaround flakes)

msune · 2025-08-15T08:38:05Z

🟢 Ready to merge. No release note necessary

msune · 2025-08-19T14:34:57Z

4 days in ready-to-merge with all green lights, yet not merged. Can someone please merge?

cc @aanm @joestringer @brb

msune requested a review from a team as a code owner August 13, 2025 14:08

msune requested a review from YutaroHayakawa August 13, 2025 14:08

maintainer-s-little-helper bot added the dont-merge/needs-release-note-label The author needs to describe the release impact of these changes. label Aug 13, 2025

smagnani96 self-requested a review August 13, 2025 16:15

smagnani96 approved these changes Aug 13, 2025

View reviewed changes

YutaroHayakawa approved these changes Aug 14, 2025

View reviewed changes

msune added 2 commits August 15, 2025 10:10

msune force-pushed the bpf_improve_trace_diff_pkts branch from 845dd37 to 399a8e9 Compare August 15, 2025 08:10

gentoo-root added the release-note/misc This PR makes changes that have no direct user impact. label Aug 15, 2025

maintainer-s-little-helper bot added ready-to-merge This PR has passed all tests and received consensus from code owners to merge. and removed dont-merge/needs-release-note-label The author needs to describe the release impact of these changes. labels Aug 15, 2025

aanm added this pull request to the merge queue Aug 19, 2025

Merged via the queue into cilium:main with commit 2c7c686 Aug 19, 2025
68 checks passed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

bpf/tests/scapy: show pkt diffs on assertion failures and improve outputs #41124

bpf/tests/scapy: show pkt diffs on assertion failures and improve outputs #41124

Uh oh!

msune commented Aug 13, 2025

Uh oh!

msune commented Aug 13, 2025

Uh oh!

msune commented Aug 15, 2025

Uh oh!

msune commented Aug 15, 2025

Uh oh!

msune commented Aug 15, 2025

Uh oh!

msune commented Aug 19, 2025

Uh oh!

Uh oh!

Uh oh!

bpf/tests/scapy: show pkt diffs on assertion failures and improve outputs #41124

bpf/tests/scapy: show pkt diffs on assertion failures and improve outputs #41124

Uh oh!

Conversation

msune commented Aug 13, 2025

Before this patch series

After:

Uh oh!

msune commented Aug 13, 2025

Uh oh!

msune commented Aug 15, 2025

Uh oh!

msune commented Aug 15, 2025

Uh oh!

msune commented Aug 15, 2025

Uh oh!

msune commented Aug 19, 2025

Uh oh!

Uh oh!

Uh oh!