diff --git a/lib/igt_aux.c b/lib/igt_aux.c
index 266aa832..b235b18c 100644
--- a/lib/igt_aux.c
+++ b/lib/igt_aux.c
@@ -984,8 +984,11 @@ void igt_debug_wait_for_keypress(const char *var)
 {
        struct termios oldt, newt;

-       if (!isatty(STDIN_FILENO))
+       if (!isatty(STDIN_FILENO)) {
+               errno = 0; /* otherwise may be ENOTTY */
                return;
+       }
+

        if (!igt_interactive_debug)
                return;

Found the culprit in this particular case. This would suppress most of the weird errno logged in kms tests. 

The questions is now: do we really want to hunt all similar cases down? A round of gdb through a couple of tests with 'watch errno' shows that it gets set to non-zero value about a dozen times every single subtest. Depending when we hit an assert we may get any of those printed out adding to confusion.

I see 3 options:
1. make sure that errno is reset to 0 by everything that touches it and change my nickname to Sisyphus
2. get rid of printing errno in igt_assert(), but then lose valuable information for all those igt_assert(write(...));
3. change igt_assert*(expr,...) macros so that they 'errno = 0;' before evaluating expr

I think that 3 makes the most sense, then we can quickly go through all the 4000-ish of calls we have to make sure that we don't have any weird 'int ret = write(); igt_assert(ret);' for those functions where errno matters.

There was a patch merged that resets errno in the few places where errno pollution is likely and in the few places where it may require resetting:

commit a558c2e2405473f4157ca71638e5a111ebfa80d1
Author: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Date:   Tue Apr 9 17:21:41 2019 +0300

    lib: Reset errno to 0 after isatty

    Since igt_assert family of functions logs last errno we get a lot of
    those: "Last errno: 25, Inappropriate ioctl for device"

    isatty() seems to be the biggest offender in that area, so this patch
    should limit amount of confusing messages significantly.

    Cc: Martin Peres <martin.peres@linux.intel.com>
    Cc: Petri Latvala <petri.latvala@intel.com>
    Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
    Reviewed-by: Petri Latvala <petri.latvala@intel.com>

commit 02b1706e8b1ca93a53d4ef0f9c484a6f1a0d18f2
Author: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Date:   Thu Apr 4 16:17:40 2019 +0300

    lib/igt_kms: Be more verbose about failure in kmstest_wait_for_pageflip

    First, we set errno to 0 before doing select() to avoid random pollution
    of the assert message with things like:
    "Last errno: 25, Inappropriate ioctl for device"

    Second, we log explicitly if we exceeded the timeout (ret == 0).

    Third, if we fail the select() we log that with some explanation.

    Cc: Petri Latvala <petri.latvala@intel.com>
    Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
    Reviewed-by: Petri Latvala <petri.latvala@intel.com>