[PATCH 3/5] generic/591: remove redundant output from golden image

[Zorro Lang <zlang@kernel.org>]

In generic/591.out expects below output:
  concurrent reader with O_DIRECT
  concurrent reader with O_DIRECT     <=== ???
  concurrent reader without O_DIRECT
  concurrent reader without O_DIRECT  <=== ???
  sequential reader with O_DIRECT
  sequential reader without O_DIRECT

The lines marked "???" are unbelievable, due to the src/splice-test.c
only calls printf to output that message once in main function. So
Why splice-test prints that message twice sometimes? It seems related
with the "-r" option, due to the test lines without "-r" option only
print one line each time running.

A stanger thing is this "double output" issue only can be triggered by
running g/591, can't reproduce it by running splice-test manually.

By checking the code of splice-test.c, I found a "fork()" in it, and
it'll be called if the '-r' option is specified. So I suspect the
redundant output come from the child process. By the help of strace
tool, I got:

  10554 execve("/root/git/xfstests/src/splice-test", ["/root/git/xfstests/src/splice-te"..., "-r", "/mnt/test/a"], 0x7ffcabc2c0a8 /* 202 vars */) = 0
  ...
  10554 clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f937f5d5a10) = 10555
  ...
  10555 read(4, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
  10555 write(1, "concurrent reader with O_DIRECT\n", 32) = 32
  10555 exit_group(0)                     = ?
  10555 +++ exited with 0 +++
  10554 <... wait4 resumed>NULL, 0, NULL) = 10555
  10554 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=10555, si_uid=0, si_status=0, si_utime=0, si_stime=1} ---
  10554 unlink("/mnt/test/a")             = 0
  10554 write(1, "concurrent reader with O_DIRECT\n", 32) = 32
  10554 exit_group(0)                     = ?
  10554 +++ exited with 0 +++

We can see the "concurrent reader with O_DIRECT\n" be printed by
parent process 10554 and child process 10555 separately.

As the output from child is unexpected and unstable. So I think we
shouldn't use it as golden image. So I add a "fflush(stdout)" to
clear the output buffer of parent process before forking a child.
Then correct the generic/591.out.

Signed-off-by: Zorro Lang <zlang@kernel.org>
---
 src/splice-test.c     | 1 +
 tests/generic/591.out | 2 --
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/splice-test.c b/src/splice-test.c
index 2f1ba2ba..e6ae6fca 100644
--- a/src/splice-test.c
+++ b/src/splice-test.c
@@ -143,6 +143,7 @@ int main(int argc, char *argv[])
 	printf("%s reader %s O_DIRECT\n",
 		   do_splice == do_splice1 ? "sequential" : "concurrent",
 		   (open_flags & O_DIRECT) ? "with" : "without");
+	fflush(stdout);
 
 	buffer = memalign(SECTOR_SIZE, BUFFER_SIZE);
 	if (buffer == NULL)
diff --git a/tests/generic/591.out b/tests/generic/591.out
index d61811ee..e9fffd1d 100644
--- a/tests/generic/591.out
+++ b/tests/generic/591.out
@@ -1,7 +1,5 @@
 QA output created by 591
 concurrent reader with O_DIRECT
-concurrent reader with O_DIRECT
-concurrent reader without O_DIRECT
 concurrent reader without O_DIRECT
 sequential reader with O_DIRECT
 sequential reader without O_DIRECT
-- 
2.31.1