[PATCH] unshare_test: set nr_open using soft limit

[lufei]

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 <lu...@uniontech.com>
---
 tools/testing/selftests/core/unshare_test.c | 28 +++++++++++++--------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/core/unshare_test.c 
b/tools/testing/selftests/core/unshare_test.c
index 7fec9dfb1b0e..2c4e7104b0d9 100644
--- a/tools/testing/selftests/core/unshare_test.c
+++ b/tools/testing/selftests/core/unshare_test.c
@@ -26,10 +26,11 @@ TEST(unshare_EMFILE)
                .exit_signal = SIGCHLD,
        };
        int fd;
-       ssize_t n, n2;
-       static char buf[512], buf2[512];
+       ssize_t n, n2, n3;
+       static char buf[512], buf2[512], buf3[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 */
+               n3 = sprintf(buf3, "%d\n", rlimit_max);
                lseek(fd, 0, SEEK_SET);
-               write(fd, buf, n);
+               write(fd, buf3, n3);
+
                /* ... 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