[PATCH i-g-t v5] lib/drmtest: Create proper error report when open driver fails

[Kamil Konieczny <kamil.konieczny@linux.intel.com>]

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

v3: break only when errno actually happens in open() (Kamil)
v4: removed 'else', removed errno printing (Zbigniew)
v5: use explicit strerror() (Kamil)

Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: Karthik B S <karthik.b.s@intel.com>
Cc: "Zbigniew Kempczyński" <zbigniew.kempczynski@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Kamil Konieczny <kamil.konieczny@linux.intel.com>
---
 lib/drmtest.c          | 26 +++++++++++++++++++++-----
 lib/drmtest.h          |  2 +-
 lib/igt_sriov_device.c |  2 +-
 3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/lib/drmtest.c b/lib/drmtest.c
index 4a788ea7a..084737edf 100644
--- a/lib/drmtest.c
+++ b/lib/drmtest.c
@@ -323,6 +323,7 @@ static void log_opened_device_path(const char *device_path)
  * __drm_open_device:
  * @name: DRM node name
  * @chipset: OR'd flags for chipset to be opened
+ * @error: pointer for saving errno when open() fails
  *
  * Open a drm legacy device node with given @name and compatible with given
  * @chipset flag.
@@ -334,8 +335,10 @@ static void log_opened_device_path(const char *device_path)
  * name, even when driver was excluded by ANY or is not listed in known drivers.
  *
  * Returns: DRM file descriptor or -1 on error
+ *
+ * When open() succeeds, sets @error to zero otherwise to errno
  */
-int __drm_open_device(const char *name, unsigned int chipset)
+int __drm_open_device(const char *name, unsigned int chipset, int *error)
 {
 	const char *forced;
 	char dev_name[16] = "";
@@ -343,8 +346,15 @@ int __drm_open_device(const char *name, unsigned int chipset)
 	int fd;
 
 	fd = open(name, O_RDWR);
-	if (fd == -1)
+	if (fd == -1) {
+		if (error)
+			*error = errno;
+
 		return -1;
+	}
+
+	if (error)
+		*error = 0;
 
 	if (__get_drm_device_name(fd, dev_name, sizeof(dev_name) - 1) == -1)
 		goto err;
@@ -426,6 +436,7 @@ static bool _is_already_opened(const char *path, int as_idx)
 static int __search_and_open(const char *base, int offset, unsigned int chipset, int as_idx)
 {
 	const char *forced;
+	int err;
 
 	forced = forced_driver();
 	if (forced)
@@ -440,9 +451,14 @@ static int __search_and_open(const char *base, int offset, unsigned int chipset,
 		if (_is_already_opened(name, as_idx))
 			continue;
 
-		fd = __drm_open_device(name, chipset);
+		fd = __drm_open_device(name, chipset, &err);
 		if (fd != -1)
 			return fd;
+
+		if (err) {
+			igt_debug("Error at open %s %s\n", name, strerror(err));
+			break;
+		}
 	}
 
 	return -1;
@@ -500,13 +516,13 @@ static int __open_driver_exact(const char *name, unsigned int chipset)
 {
 	int fd;
 
-	fd = __drm_open_device(name, chipset);
+	fd = __drm_open_device(name, chipset, NULL);
 	if (fd != -1)
 		return fd;
 
 	drm_load_module(chipset);
 
-	return __drm_open_device(name, chipset);
+	return __drm_open_device(name, chipset, NULL);
 }
 
 /*
diff --git a/lib/drmtest.h b/lib/drmtest.h
index 37874d729..126feffda 100644
--- a/lib/drmtest.h
+++ b/lib/drmtest.h
@@ -117,7 +117,7 @@ unsigned int drm_get_chipset(int fd);
  */
 #define IS_ALIGNED(v, a)	(((v) & ((typeof(v))(a) - 1)) == 0)
 
-int __drm_open_device(const char *name, unsigned int chipset);
+int __drm_open_device(const char *name, unsigned int chipset, int *error);
 void drm_load_module(unsigned int chipset);
 int drm_open_driver_another(int idx, int chipset);
 int drm_open_driver(int chipset);
diff --git a/lib/igt_sriov_device.c b/lib/igt_sriov_device.c
index 1f4c3ac04..21d23298b 100644
--- a/lib/igt_sriov_device.c
+++ b/lib/igt_sriov_device.c
@@ -284,7 +284,7 @@ int igt_sriov_open_vf_drm_device(int pf, unsigned int vf_num)
 	if (!found)
 		return -1;
 
-	fd = __drm_open_device(dev_name, DRIVER_ANY);
+	fd = __drm_open_device(dev_name, DRIVER_ANY, NULL);
 	if (fd >= 0 && is_xe_device(fd))
 		xe_device_get(fd);
 
-- 
2.54.0