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selftests/bpf: test_progs: fix verbose mode garbage 

fseeko(.., 0, SEEK_SET) on a memstream just puts the buffer pointer
to the beginning so when we call fflush on it we get some garbage
log data from the previous test. Let's manually set terminating
byte to zero at the reported buffer size.

To show the issue consider the following snippet:

	stream = open_memstream (&buf, &len);

	fprintf(stream, "aaa");
	fflush(stream);
	printf("buf=%s, len=%zu\n", buf, len);
	fseeko(stream, 0, SEEK_SET);

	fprintf(stream, "b");
	fflush(stream);
	printf("buf=%s, len=%zu\n", buf, len);

Output:

	buf=aaa, len=3
	buf=baa, len=1

Fixes: 946152b3c5 ("selftests/bpf: test_progs: switch to open_memstream")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Stanislav Fomichev 2019-08-30 19:34:26 -07:00 committed by Daniel Borkmann
parent bdb15a29cc
commit d80507d15d
1 changed files with 1 additions and 0 deletions
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1
tools/testing/selftests/bpf/test_progs.c
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@ -45,6 +45,7 @@ static void dump_test_log(const struct prog_test_def *test, bool failed)
if (env.verbose || test->force_log || failed) {
if (env.log_cnt) {
env.log_buf[env.log_cnt] = '\0';
fprintf(env.stdout, "%s", env.log_buf);
if (env.log_buf[env.log_cnt - 1] != '\n')
fprintf(env.stdout, "\n");