On 11/4/25 01:30, Kuniyuki Iwashima wrote:
On Mon, Nov 3, 2025 at 4:08 PM Sunday Adelodun adelodunolaoluwa@yahoo.com wrote:
On 11/2/25 08:32, Kuniyuki Iwashima wrote:
On Sat, Nov 1, 2025 at 10:23 AM Sunday Adelodun adelodunolaoluwa@yahoo.com wrote:
Add selftests to verify and document Linux’s intended behaviour for UNIX domain sockets (SOCK_STREAM and SOCK_DGRAM) when a peer closes. The tests verify that:
- SOCK_STREAM returns EOF when the peer closes normally.
- SOCK_STREAM returns ECONNRESET if the peer closes with unread data.
- SOCK_SEQPACKET returns EOF when the peer closes normally.
- SOCK_SEQPACKET returns ECONNRESET if the peer closes with unread data.
- SOCK_DGRAM does not return ECONNRESET when the peer closes.
This follows up on review feedback suggesting a selftest to clarify Linux’s semantics.
Suggested-by: Kuniyuki Iwashima kuniyu@google.com Signed-off-by: Sunday Adelodun adelodunolaoluwa@yahoo.com
tools/testing/selftests/net/af_unix/Makefile | 1 + .../selftests/net/af_unix/unix_connreset.c | 179 ++++++++++++++++++ 2 files changed, 180 insertions(+) create mode 100644 tools/testing/selftests/net/af_unix/unix_connreset.c
diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile index de805cbbdf69..5826a8372451 100644 --- a/tools/testing/selftests/net/af_unix/Makefile +++ b/tools/testing/selftests/net/af_unix/Makefile @@ -7,6 +7,7 @@ TEST_GEN_PROGS := \ scm_pidfd \ scm_rights \ unix_connect \
unix_connreset \patchwork caught this test is not added to .gitignore. https://patchwork.kernel.org/project/netdevbpf/patch/20251101172230.10179-1-...
Could you add it to this file ?
tools/testing/selftests/net/.gitignore
Oh, thank you for this. will add it
# end of TEST_GEN_PROGS
include ../../lib.mk diff --git a/tools/testing/selftests/net/af_unix/unix_connreset.c b/tools/testing/selftests/net/af_unix/unix_connreset.c new file mode 100644 index 000000000000..6f43435d96e2 --- /dev/null +++ b/tools/testing/selftests/net/af_unix/unix_connreset.c @@ -0,0 +1,179 @@ +// SPDX-License-Identifier: GPL-2.0 +/*
- Selftest for AF_UNIX socket close and ECONNRESET behaviour.
- This test verifies:
- SOCK_STREAM returns EOF when the peer closes normally.
- SOCK_STREAM returns ECONNRESET if peer closes with unread data.
- SOCK_SEQPACKET returns EOF when the peer closes normally.
- SOCK_SEQPACKET returns ECONNRESET if the peer closes with unread data.
- SOCK_DGRAM does not return ECONNRESET when the peer closes.
- These tests document the intended Linux behaviour.
- */
+#define _GNU_SOURCE +#include <stdlib.h> +#include <string.h> +#include <fcntl.h> +#include <unistd.h> +#include <errno.h> +#include <sys/socket.h> +#include <sys/un.h> +#include "../../kselftest_harness.h"
+#define SOCK_PATH "/tmp/af_unix_connreset.sock"
+static void remove_socket_file(void) +{
unlink(SOCK_PATH);+}
+FIXTURE(unix_sock) +{
int server;int client;int child;+};
+FIXTURE_VARIANT(unix_sock) +{
int socket_type;const char *name;+};
+/* Define variants: stream and datagram */
nit: outdated, maybe simply remove ?
oh..skipped me. will do so.
+FIXTURE_VARIANT_ADD(unix_sock, stream) {
.socket_type = SOCK_STREAM,.name = "SOCK_STREAM",+};
+FIXTURE_VARIANT_ADD(unix_sock, dgram) {
.socket_type = SOCK_DGRAM,.name = "SOCK_DGRAM",+};
+FIXTURE_VARIANT_ADD(unix_sock, seqpacket) {
.socket_type = SOCK_SEQPACKET,.name = "SOCK_SEQPACKET",+};
+FIXTURE_SETUP(unix_sock) +{
struct sockaddr_un addr = {};int err;addr.sun_family = AF_UNIX;strcpy(addr.sun_path, SOCK_PATH);remove_socket_file();self->server = socket(AF_UNIX, variant->socket_type, 0);ASSERT_LT(-1, self->server);err = bind(self->server, (struct sockaddr *)&addr, sizeof(addr));ASSERT_EQ(0, err);if (variant->socket_type == SOCK_STREAM ||variant->socket_type == SOCK_SEQPACKET) {patchwork caught mis-alignment here and other places.
I'm using this for emacs, and other editors will have a similar config.
(setq-default c-default-style "linux")
You can check if lines are aligned properly by
$ git show --format=email | ./scripts/checkpatch.pl
err = listen(self->server, 1);ASSERT_EQ(0, err);self->client = socket(AF_UNIX, variant->socket_type, 0);Could you add SOCK_NONBLOCK here too ?
This is noted
ASSERT_LT(-1, self->client);err = connect(self->client, (struct sockaddr *)&addr, sizeof(addr));ASSERT_EQ(0, err);self->child = accept(self->server, NULL, NULL);ASSERT_LT(-1, self->child);} else {/* Datagram: bind and connect only */self->client = socket(AF_UNIX, SOCK_DGRAM | SOCK_NONBLOCK, 0);ASSERT_LT(-1, self->client);err = connect(self->client, (struct sockaddr *)&addr, sizeof(addr));ASSERT_EQ(0, err);}+}
+FIXTURE_TEARDOWN(unix_sock) +{
if (variant->socket_type == SOCK_STREAM ||variant->socket_type == SOCK_SEQPACKET)close(self->child);close(self->client);close(self->server);remove_socket_file();+}
+/* Test 1: peer closes normally */ +TEST_F(unix_sock, eof) +{
char buf[16] = {};ssize_t n;/* Peer closes normally */if (variant->socket_type == SOCK_STREAM ||variant->socket_type == SOCK_SEQPACKET)close(self->child);elseclose(self->server);n = recv(self->client, buf, sizeof(buf), 0);TH_LOG("%s: recv=%zd errno=%d (%s)", variant->name, n, errno, strerror(errno));errno is undefined if not set, and same for strerror(errno).
Also, if ASSERT_XXX() below fails, the same information (test case, errno) is logged. So, TH_LOG() seems unnecessary.
Maybe try modifying the condition below and see how the assertion is logged.
Oh..thank you. Didn't it through that way. I understand. I will remove the TH_LOG()'s
if (variant->socket_type == SOCK_STREAM ||variant->socket_type == SOCK_SEQPACKET) {ASSERT_EQ(0, n);} else {ASSERT_EQ(-1, n);ASSERT_EQ(EAGAIN, errno);}+}
+/* Test 2: peer closes with unread data */ +TEST_F(unix_sock, reset_unread) +{
char buf[16] = {};ssize_t n;/* Send data that will remain unread by client */send(self->client, "hello", 5, 0);close(self->child);n = recv(self->client, buf, sizeof(buf), 0);TH_LOG("%s: recv=%zd errno=%d (%s)", variant->name, n, errno, strerror(errno));if (variant->socket_type == SOCK_STREAM ||variant->socket_type == SOCK_SEQPACKET) {ASSERT_EQ(-1, n);ASSERT_EQ(ECONNRESET, errno);} else {ASSERT_EQ(-1, n);ASSERT_EQ(EAGAIN, errno);}+}
+/* Test 3: SOCK_DGRAM peer close */ Now Test 2 and Test 3 look identical ;)
seems so, but the only difference is:
close(self->child); is used in Test 2, while close(self->server); is used in Test 3. Maybe I should find a way to collapse Tests 2 and 3 (if statement might work)
I am just afraid the tests to run will reduce to 6 from 9 and we will have 6 cases passed as against 7 as before.
What do you think?
The name of Test 2 is a bit confusing, which is not true for SOCK_DGRAM. So, I'd use "if" to change which fd to close() depending on the socket type.
Also, close(self->server) does nothing for SOCK_STREAM and SOCK_SEQPACKET after accept(). Rather, that close() should have the same effect if self->child is not accept()ed. (In this case, Skip() for SOCK_DGRAM makes sense)
I think covering that scenario would be nicer.
If interested, you can check the test coverage with this patch. https://lore.kernel.org/linux-kselftest/20251028024339.2028774-1-kuniyu@goog...
Thanks!
Thank you!
kindly check these if any conforms to what it should be:
TEST_F(unix_sock, reset_unread_behavior) { char buf[16] = {}; ssize_t n;
/* Send data that will remain unread by client */ send(self->client, "hello", 5, 0);
if (variant->socket_type == SOCK_DGRAM) { close(self->server); } else { if (!self->child) SKIP(return);
close(self->child); }
n = recv(self->client, buf, sizeof(buf), 0);
ASSERT_EQ(-1, n);
if (variant->socket_type == SOCK_STREAM || variant->socket_type == SOCK_SEQPACKET) do { ASSERT_EQ(ECONNRESET, errno); } while (0); else ASSERT_EQ(EAGAIN, errno); }
OR
TEST_F(unix_sock, reset_unread_behavior) { char buf[16] = {}; ssize_t n;
/* Send data that will remain unread by client */ send(self->client, "hello", 5, 0);
if (variant->socket_type == SOCK_DGRAM) { close(self->server); } else { if (self->child) close(self->child); else close(self->server); }
n = recv(self->client, buf, sizeof(buf), 0);
ASSERT_EQ(-1, n);
if (variant->socket_type == SOCK_STREAM || variant->socket_type == SOCK_SEQPACKET) do { ASSERT_EQ(ECONNRESET, errno); } while (0); else ASSERT_EQ(EAGAIN, errno); }
OR
is there a better way to handle this?
I ran the KCOV_OUTPUT command using the first *TEST_F above* as the Test 2 and got the output below: *$ KCOV_OUTPUT=kcov KCOV_SLOTS=8192 ./tools/testing/selftests/net/af_unix/unix_connreset* TAP version 13 1..6 # Starting 6 tests from 3 test cases. # RUN unix_sock.stream.eof ... # OK unix_sock.stream.eof ok 1 unix_sock.stream.eof # RUN unix_sock.stream.reset_unread_behavior ... # OK unix_sock.stream.reset_unread_behavior ok 2 unix_sock.stream.reset_unread_behavior # RUN unix_sock.dgram.eof ... # OK unix_sock.dgram.eof ok 3 unix_sock.dgram.eof # RUN unix_sock.dgram.reset_unread_behavior ... # OK unix_sock.dgram.reset_unread_behavior ok 4 unix_sock.dgram.reset_unread_behavior # RUN unix_sock.seqpacket.eof ... # OK unix_sock.seqpacket.eof ok 5 unix_sock.seqpacket.eof # RUN unix_sock.seqpacket.reset_unread_behavior ... # OK unix_sock.seqpacket.reset_unread_behavior ok 6 unix_sock.seqpacket.reset_unread_behavior # PASSED: 6 / 6 tests passed. # Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0
Thank you once again for your continuous guidance and patience. It's a worthy and rewarding learning period for me.