Re: [Qemu-devel] [PATCH] tests/boot-serial-test: Fix problem with timeout due to dropped characters

[Thomas Huth]

On 16.02.2018 11:15, Peter Maydell wrote:
> On 16 February 2018 at 06:12, Thomas Huth <address@hidden> wrote:
>> Commit 92b540dac9fc3a5 introduce a counter to handle the timeouts in a
>> better way. But in case ccnt reaches 512, the current read character is
>> ignored - and if that character is part of the string that we are looking
>> for, the test fails to match the string.
>>
>> Almost all of the tests look for a string within the first 512 bytes of
>> firmware output, so the problem never triggered there. But the hppa test
>> that has been added recently looks for a longer string at the very end of
>> a long output, thus there's a chance that we miss a character there so
>> that the test fails unexpectedly. Fix it by *not* reading and dropping a
>> character if the counter reaches 512.
>>
>> Fixes: 92b540dac9fc3a572c7342edd0b073000f5a6abf
>> Signed-off-by: Thomas Huth <address@hidden>
>> ---
>>  @Peter: Since this fixes the problem with running "make check", could
>>  you maybe apply this directly to the master branch? Thanks, and sorry
>>  for the inconvenience!
>>
>>  tests/boot-serial-test.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tests/boot-serial-test.c b/tests/boot-serial-test.c
>> index ea87a80..696f7a3 100644
>> --- a/tests/boot-serial-test.c
>> +++ b/tests/boot-serial-test.c
>> @@ -101,7 +101,7 @@ static void check_guest_output(const testdef_t *test, 
>> int fd)
>>      /* Poll serial output... Wait at most 60 seconds */
>>      for (i = 0; i < 6000; ++i) {
>>          ccnt = 0;
>> -        while ((nbr = read(fd, &ch, 1)) == 1 && ccnt++ < 512) {
>> +        while (ccnt++ < 512 && (nbr = read(fd, &ch, 1)) == 1) {
>>              if (ch == test->expect[pos]) {
>>                  pos += 1;
>>                  if (test->expect[pos] == '\0') {
> 
> I did a test build with this, but OpenBSD's compiler
> now complains:
> 
> /home/qemu/tests/boot-serial-test.c: In function 'test_machine':
> /usr/local/include/glib-2.0/glib/gmacros.h:370:7: warning: 'nbr' may
> be used uninitialized in this function [-Wmaybe-uninitialized]
>     if (expr)                                    \
>        ^
> /home/qemu/tests/boot-serial-test.c:114:12: note: 'nbr' was declared here
>      int i, nbr, pos = 0, ccnt;
>             ^
> 
> This is obviously a false positive, but we can silence it by
> --- a/tests/boot-serial-test.c
> +++ b/tests/boot-serial-test.c
> @@ -111,7 +111,7 @@ static testdef_t tests[] = {
>  static void check_guest_output(const testdef_t *test, int fd)
>  {
>      bool output_ok = false;
> -    int i, nbr, pos = 0, ccnt;
> +    int i, nbr = 0, pos = 0, ccnt;
>      char ch;
> 
>      /* Poll serial output... Wait at most 60 seconds */
> 
> so I'll just squash that change in if that's ok?

Sure!

 Thanks,
  Thomas


PS: I think the OpenBSD compiler is wrong here, nbr should get
initialized at least once before the g_assert(nbr >= 0) check ...