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

[Peter Maydell]

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?

thanks
-- PMM