[PATCH v2] unshare_test: set nr_open using soft limit

[lufei <lufei@uniontech.com>]

Set maximum file descriptor number limit by rlimit.rlim_max than
nr_open(hard limit). Hard limit may cause dup2 fail.

Signed-off-by: lufei <lufei@uniontech.com>
---
 tools/testing/selftests/core/unshare_test.c | 24 ++++++++++++++-------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/core/unshare_test.c b/tools/testing/selftests/core/unshare_test.c
index 7fec9dfb1b0e..66b651168887 100644
--- a/tools/testing/selftests/core/unshare_test.c
+++ b/tools/testing/selftests/core/unshare_test.c
@@ -30,6 +30,7 @@ TEST(unshare_EMFILE)
 	static char buf[512], buf2[512];
 	struct rlimit rlimit;
 	int nr_open;
+	int rlimit_max;
 
 	fd = open("/proc/sys/fs/nr_open", O_RDWR);
 	ASSERT_GE(fd, 0);
@@ -42,22 +43,24 @@ TEST(unshare_EMFILE)
 
 	ASSERT_EQ(0, getrlimit(RLIMIT_NOFILE, &rlimit));
 
-	/* bump fs.nr_open */
-	n2 = sprintf(buf2, "%d\n", nr_open + 1024);
+	rlimit_max = rlimit.rlim_max;
+
+	/* bump rlimit.rlim_max */
+	n2 = sprintf(buf2, "%d\n", rlimit_max + 1024);
 	lseek(fd, 0, SEEK_SET);
 	write(fd, buf2, n2);
 
 	/* bump ulimit -n */
-	rlimit.rlim_cur = nr_open + 1024;
-	rlimit.rlim_max = nr_open + 1024;
+	rlimit.rlim_cur = rlimit_max + 1024;
+	rlimit.rlim_max = rlimit_max + 1024;
 	EXPECT_EQ(0, setrlimit(RLIMIT_NOFILE, &rlimit)) {
 		lseek(fd, 0, SEEK_SET);
 		write(fd, buf, n);
 		exit(EXIT_FAILURE);
 	}
 
-	/* get a descriptor past the old fs.nr_open */
-	EXPECT_GE(dup2(2, nr_open + 64), 0) {
+	/* get a descriptor past the old rlimit.rlim_max */
+	EXPECT_GE(dup2(2, rlimit_max + 64), 0) {
 		lseek(fd, 0, SEEK_SET);
 		write(fd, buf, n);
 		exit(EXIT_FAILURE);
@@ -74,15 +77,20 @@ TEST(unshare_EMFILE)
 	if (pid == 0) {
 		int err;
 
-		/* restore fs.nr_open */
+		n2 = sprintf(buf2, "%d\n", rlimit_max);
 		lseek(fd, 0, SEEK_SET);
-		write(fd, buf, n);
+		write(fd, buf2, n2);
+
 		/* ... and now unshare(CLONE_FILES) must fail with EMFILE */
 		err = unshare(CLONE_FILES);
 		EXPECT_EQ(err, -1)
 			exit(EXIT_FAILURE);
 		EXPECT_EQ(errno, EMFILE)
 			exit(EXIT_FAILURE);
+
+		/* restore fs.nr_open */
+		lseek(fd, 0, SEEK_SET);
+		write(fd, buf, n);
 		exit(EXIT_SUCCESS);
 	}
 
-- 
2.39.3