On Thu, Aug 12, 2021 at 9:46 AM Kuniyuki Iwashima [off-list ref] wrote:

The iterator can output almost the same result compared to /proc/net/unix.
The header line is aligned, and the Inode column uses "%8lu" because "%5lu"
can be easily overflown.

  # cat /sys/fs/bpf/unix
  Num               RefCount Protocol Flags    Type St Inode    Path

It's totally my OCD, but why the column name is not aligned with
values? I mean the "Inode" column. It's left aligned, but values
(numbers) are right-aligned? I'd fix that while applying, but I can't
apply due to selftests failures, so please take a look.

  ffff963c06689800: 00000002 00000000 00010000 0001 01    18697 private/defer
  ffff963c7c979c00: 00000002 00000000 00000000 0001 01   598245 @Hello@World@

  # cat /proc/net/unix
  Num       RefCount Protocol Flags    Type St Inode Path
  ffff963c06689800: 00000002 00000000 00010000 0001 01 18697 private/defer
  ffff963c7c979c00: 00000002 00000000 00000000 0001 01 598245 @Hello@World@

Note that this prog requires the patch ([0]) for LLVM code gen.  Thanks to
Yonghong Song for analysing and fixing.

[0] https://reviews.llvm.org/D107483

Signed-off-by: Kuniyuki Iwashima <redacted>
Acked-by: Yonghong Song <redacted>
---

This selftests breaks test_progs-no_alu32 ([0], the error log is super
long and can freeze browser; it looks like an infinite loop and BPF
verifier just keeps reporting it until it runs out of 1mln
instructions or something). Please check what's going on there, I
can't land it as it is right now.

  [0] https://github.com/kernel-patches/bpf/runs/3326071112?check_suite_focus=true#step:6:124288

 tools/testing/selftests/bpf/README.rst        | 38 +++++++++
 .../selftests/bpf/prog_tests/bpf_iter.c       | 16 ++++
 tools/testing/selftests/bpf/progs/bpf_iter.h  |  8 ++
 .../selftests/bpf/progs/bpf_iter_unix.c       | 77 +++++++++++++++++++
 .../selftests/bpf/progs/bpf_tracing_net.h     |  4 +
 5 files changed, 143 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_unix.c

[...]

+                       /* The name of the abstract UNIX domain socket starts
+                        * with '\0' and can contain '\0'.  The null bytes
+                        * should be escaped as done in unix_seq_show().
+                        */
+                       int i, len;
+

no_alu32 variant probably isn't happy about using int for this, it
probably does << 32, >> 32 dance and loses track of actual value in
the loop. You can try using u64 instead.

+                       len = unix_sk->addr->len - sizeof(short);
+
+                       BPF_SEQ_PRINTF(seq, " @");
+
+                       /* unix_mkname() tests this upper bound. */
+                       if (len < sizeof(struct sockaddr_un))
+                               for (i = 1; i < len; i++)

if you move above if inside the loop to break out of the loop, does it
change how Clang generates code?

for (i = 1; i < len i++) {
    if (i >= sizeof(struct sockaddr_un))
        break;
    BPF_SEQ_PRINTF(...);
}