Re: [PATCH i-g-t v2] lib/drmtest: Create proper error report when open driver fails

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 21 Apr 2026, Kamil Konieczny <kamil.konieczny@linux.intel.com> wrote:
> When first try for opening driver fails then opening function is
> searching for next available device. When that also fails
> reporting is printing last errno which could mislead developer:
>
> $ build/tests/kms_dp_aux_dev
> IGT-Version: 2.3-NO-GIT (x86_64) (Linux: 6.17.0-19-generic x86_64)
> Test requirement not met in function drm_open_driver, file ../lib/drmtest.c:754:
> Test requirement: !(fd<0)
> No known gpu found for chipset flags 0x4294965755 (any)
> Last errno: 2, No such file or directory
> SKIP (0.006s)
>
> ls /dev/dri
> by-path  card1  renderD128
>
> The real problem here is lack of permissions as there was a card
> but program could not open it. Break looking for a card as soon
> as an error is different from ENOENT. It will create a proper
> error report which will print:
>
> Last errno: 13, Permission denied

Isn't it also a problem that errno is really only valid right after a
failed libc call, and unspecified later?

All asserts lead to __igt_fail_assert(), which logs the last errno, but
anything could've happened before then. Most crucially, the errno
could've happened and been handled a while back, but the subsequent libc
calls won't clear the previous errno on success. So errno at assert
might have nothing to do with the assert itself.

BR,
Jani.

>
> Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
> Cc: Karthik B S <karthik.b.s@intel.com>
> Cc: "Zbigniew Kempczyński" <zbigniew.kempczynski@intel.com>
> Signed-off-by: Kamil Konieczny <kamil.konieczny@linux.intel.com>
> ---
>  lib/drmtest.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/lib/drmtest.c b/lib/drmtest.c
> index 4a788ea7a..66982f653 100644
> --- a/lib/drmtest.c
> +++ b/lib/drmtest.c
> @@ -443,6 +443,11 @@ static int __search_and_open(const char *base, int offset, unsigned int chipset,
>  		fd = __drm_open_device(name, chipset);
>  		if (fd != -1)
>  			return fd;
> +
> +		if (errno == ENOENT)
> +			continue;
> +
> +		break;
>  	}
>  
>  	return -1;

-- 
Jani Nikula, Intel