From: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Date: Wed, 11 Aug 2021 14:15:50 -0700
> On Tue, Aug 10, 2021 at 2:29 AM Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx> wrote:
> >
> > /proc/net/unix uses "%c" to print a single-byte character to escape '\0' in
> > the name of the abstract UNIX domain socket. The following selftest uses
> > it, so this patch adds support for "%c". Note that it does not support
> > wide character ("%lc" and "%llc") for simplicity.
> >
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx>
> > ---
> > kernel/bpf/helpers.c | 14 ++++++++++++++
> > 1 file changed, 14 insertions(+)
> >
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index 15746f779fe1..6d3aaf94e9ac 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -907,6 +907,20 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
> > tmp_buf += err;
> > num_spec++;
> >
> > + continue;
> > + } else if (fmt[i] == 'c') {
>
> you are adding new features to printk-like helpers, please add
> corresponding tests as well. I'm particularly curious how something
> like "% 9c" (which is now allowed, along with a few other unusual
> combinations) will work.
I see. I'll add a test.
I'm now thinking of test like:
1. pin the bpf prog that outputs "% 9c" and other format strings.
2. read and validate it
Is there any related test ?
and is there other complicated fomat strings to test ?
Also, "% 9c" worked as is :)
---8<---
$ sudo ./tools/bpftool/bpftool iter pin ./bpf_iter_unix.o /sys/fs/bpf/unix
$ sudo cat /sys/fs/bpf/unix | head -n 1
a
$ git diff
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_unix.c b/tools/testing/selftests/bpf/progs/bpf_iter_unix.c
index ad397e2962cf..8a7d5aa4c054 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter_unix.c
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_unix.c
@@ -34,8 +34,10 @@ int dump_unix(struct bpf_iter__unix *ctx)
seq = ctx->meta->seq;
seq_num = ctx->meta->seq_num;
- if (seq_num == 0)
+ if (seq_num == 0) {
+ BPF_SEQ_PRINTF(seq, "% 9c\n", 'a');
BPF_SEQ_PRINTF(seq, "Num RefCount Protocol Flags Type St Inode Path\n");
+ }
BPF_SEQ_PRINTF(seq, "%pK: %08X %08X %08X %04X %02X %8lu",
unix_sk,
---8<---
>
> > + if (!tmp_buf)
> > + goto nocopy_fmt;
> > +
> > + if (tmp_buf_end == tmp_buf) {
> > + err = -ENOSPC;
> > + goto out;
> > + }
> > +
> > + *tmp_buf = raw_args[num_spec];
> > + tmp_buf++;
> > + num_spec++;
> > +
> > continue;
> > }
> >
> > --
> > 2.30.2
