[LTP] [PATCH 3/8] syscalls: Add epoll_wait09

[Cyril Hrubis <chrubis@suse.cz>]

That checks that events from recursive epoll are propagated correctly.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---
 runtest/syscalls                              |   2 +-
 .../kernel/syscalls/epoll_wait/.gitignore     |   1 +
 .../kernel/syscalls/epoll_wait/epoll_wait09.c | 132 ++++++++++++++++++
 3 files changed, 134 insertions(+), 1 deletion(-)
 create mode 100644 testcases/kernel/syscalls/epoll_wait/epoll_wait09.c

diff --git a/runtest/syscalls b/runtest/syscalls
index 0c6bcdd1a..cf4352d05 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -195,7 +195,7 @@ epoll_wait04 epoll_wait04
 epoll_wait05 epoll_wait05
 epoll_wait06 epoll_wait06
 epoll_wait07 epoll_wait07
-epoll_wait08 epoll_wait08
+epoll_wait09 epoll_wait09
 
 epoll_pwait01 epoll_pwait01
 epoll_pwait02 epoll_pwait02
diff --git a/testcases/kernel/syscalls/epoll_wait/.gitignore b/testcases/kernel/syscalls/epoll_wait/.gitignore
index f3b208950..f32ec535b 100644
--- a/testcases/kernel/syscalls/epoll_wait/.gitignore
+++ b/testcases/kernel/syscalls/epoll_wait/.gitignore
@@ -6,3 +6,4 @@ epoll_wait05
 epoll_wait06
 epoll_wait07
 epoll_wait08
+epoll_wait09
diff --git a/testcases/kernel/syscalls/epoll_wait/epoll_wait09.c b/testcases/kernel/syscalls/epoll_wait/epoll_wait09.c
new file mode 100644
index 000000000..790690884
--- /dev/null
+++ b/testcases/kernel/syscalls/epoll_wait/epoll_wait09.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Cyril Hrubis <chrubis@suse.cz>
+ */
+
+/*\
+ * Verify that epoll_wait works with nested epoll instances up to the maximum
+ * nesting depth of 5 allowed by the kernel (EP_MAX_NESTS).
+ *
+ * [Algorithm]
+ *
+ * - Create a pipe.
+ * - Build a chain of epoll instances of the given depth where the innermost
+ *   monitors the pipe read end and each subsequent one monitors the previous.
+ * - Write data to the pipe.
+ * - Call epoll_wait on the outermost epoll instance and verify it reports
+ *   EPOLLIN.
+ * - Walk the chain inward calling epoll_wait on each level and verify that
+ *   every level reports EPOLLIN on the expected fd.
+ * - Read the data from the pipe to drain it.
+ */
+
+#include <sys/epoll.h>
+
+#include "tst_epoll.h"
+#include "tst_test.h"
+
+#define MAX_DEPTH 5
+
+static int epfds[MAX_DEPTH];
+static int fds[2] = {-1, -1};
+
+static struct tcase {
+	int depth;
+} tcases[] = {
+	{2},
+	{3},
+	{4},
+	{5},
+};
+
+static void run(unsigned int n)
+{
+	struct tcase *tc = &tcases[n];
+	struct epoll_event ev;
+	int prev_fd, i;
+	char buf;
+
+	prev_fd = fds[0];
+
+	for (i = 0; i < tc->depth; i++) {
+		epfds[i] = SAFE_EPOLL_CREATE1(0);
+
+		ev.events = EPOLLIN;
+		ev.data.fd = prev_fd;
+
+		SAFE_EPOLL_CTL(epfds[i], EPOLL_CTL_ADD, prev_fd, &ev);
+
+		prev_fd = epfds[i];
+	}
+
+	SAFE_WRITE(SAFE_WRITE_ALL, fds[1], "x", 1);
+
+	/* Walk from outermost to innermost verifying each level */
+	for (i = tc->depth - 1; i >= 0; i--) {
+		int expected_fd = (i > 0) ? epfds[i - 1] : fds[0];
+
+		TEST(epoll_wait(epfds[i], &ev, 1, 1000));
+		if (TST_RET != 1) {
+			tst_res(TFAIL | TTERRNO,
+				"depth %d/%d: epoll_wait() returned %li, expected 1",
+				tc->depth - i, tc->depth, TST_RET);
+			goto end;
+		}
+
+		if (ev.data.fd != expected_fd) {
+			tst_res(TFAIL,
+				"depth %d/%d: data.fd %d, expected %d",
+				tc->depth - i, tc->depth,
+				ev.data.fd, expected_fd);
+			goto end;
+		}
+
+		if (!(ev.events & EPOLLIN)) {
+			tst_res(TFAIL,
+				"depth %d/%d: events %x, expected EPOLLIN",
+				tc->depth - i, tc->depth, ev.events);
+			goto end;
+		}
+	}
+
+	tst_res(TPASS, "epoll_wait() with %d nested levels", tc->depth);
+
+end:
+	SAFE_READ(1, fds[0], &buf, 1);
+
+	for (i = tc->depth - 1; i >= 0; i--) {
+		if (epfds[i] != -1)
+			SAFE_CLOSE(epfds[i]);
+	}
+
+}
+
+static void setup(void)
+{
+	int i;
+
+	for (i = 0; i < MAX_DEPTH; i++)
+		epfds[i] = -1;
+
+	SAFE_PIPE(fds);
+}
+
+static void cleanup(void)
+{
+	int i;
+
+	for (i = 0; i < MAX_DEPTH; i++) {
+		if (epfds[i] != -1)
+			SAFE_CLOSE(epfds[i]);
+	}
+
+	SAFE_CLOSE(fds[0]);
+	SAFE_CLOSE(fds[1]);
+}
+
+static struct tst_test test = {
+	.test = run,
+	.setup = setup,
+	.cleanup = cleanup,
+	.tcnt = ARRAY_SIZE(tcases),
+};
-- 
2.52.0


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