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Tue, 09 Sep 2025 03:15:28 -0700 (PDT) From: Jakub Sitnicki To: Michal Luczaj Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Mykola Lysenko , Shuah Khan , bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next 1/5] selftests/bpf: sockmap_redir: Simplify try_recv() In-Reply-To: <87ikhs54z2.fsf@cloudflare.com> (Jakub Sitnicki's message of "Tue, 09 Sep 2025 11:51:13 +0200") References: <20250905-redir-test-pass-drop-v1-0-9d9e43ff40df@rbox.co> <20250905-redir-test-pass-drop-v1-1-9d9e43ff40df@rbox.co> <87ikhs54z2.fsf@cloudflare.com> Date: Tue, 09 Sep 2025 12:15:27 +0200 Message-ID: <87bjnk53uo.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Tue, Sep 09, 2025 at 11:51 AM +02, Jakub Sitnicki wrote: > On Fri, Sep 05, 2025 at 01:11 PM +02, Michal Luczaj wrote: >> try_recv() was meant to support both @expect_success cases, but all the >> callers use @expect_success=false anyway. Drop the unused logic and fold in >> MSG_DONTWAIT. Adapt callers. >> >> Subtle change here: recv() return value of 0 will also be considered (an >> unexpected) success. >> >> Signed-off-by: Michal Luczaj >> --- >> .../selftests/bpf/prog_tests/sockmap_redir.c | 25 +++++++++------------- >> 1 file changed, 10 insertions(+), 15 deletions(-) >> >> diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_redir.c b/tools/testing/selftests/bpf/prog_tests/sockmap_redir.c >> index 9c461d93113db20de65ac353f92dfdbe32ffbd3b..c1bf1076e8152b7d83c3e07e2dce746b5a39cf7e 100644 >> --- a/tools/testing/selftests/bpf/prog_tests/sockmap_redir.c >> +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_redir.c >> @@ -144,17 +144,14 @@ static void get_redir_params(struct redir_spec *redir, >> *redirect_flags = 0; >> } >> >> -static void try_recv(const char *prefix, int fd, int flags, bool expect_success) >> +static void fail_recv(const char *prefix, int fd, int more_flags) >> { >> ssize_t n; >> char buf; >> >> - errno = 0; >> - n = recv(fd, &buf, 1, flags); >> - if (n < 0 && expect_success) >> - FAIL_ERRNO("%s: unexpected failure: retval=%zd", prefix, n); >> - if (!n && !expect_success) >> - FAIL("%s: expected failure: retval=%zd", prefix, n); >> + n = recv(fd, &buf, 1, MSG_DONTWAIT | more_flags); >> + if (n >= 0) >> + FAIL("%s: unexpected success: retval=%zd", prefix, n); >> } > > This bit, which you highlighted in the description, I don't get. > > If we're expecting to receive exactly one byte, why treat a short read > as a succcess? Why not make it a strict "n != 1" check? > > [...] Nevermind. It makes sense now. We do want to report a failure for 0-len msg recv as well. You're effectively checking if the rcv queue is empty. I'd add MSG_PEEK, to signal that we're _just checking_ if the socket is readable, and turn the check into the below to succeed only when queue is empty: (n != -1 || (errno != EAGAIN && errno != EWOULDBLOCK)) It's a minor thing. Leaving it up to you. Either way: Reviewed-by: Jakub Sitnicki