[PATCH RESEND i-g-t v4 06/31] lib/igt_drm_stub: introduce for tools needing driver detection

Add drm/pciaccess-dependent stubs into a new igt_drm_stub.c.  This avoids
pulling libdrm into tools that only need dep-free logging and exit stubs.

The new lib_igt_drm_stub static sub-library provides: igt_pci_system_init,
is_i915_device, is_intel_device, xe_dev_id and __drm_open_driver.

Signed-off-by: Sebastian Brzezinka <[email protected]>
Acked-by: Ashutosh Dixit <[email protected]>
Reviewed-by: Krzysztof Niemiec <[email protected]>
Reviewed-by: Krzysztof Karas <[email protected]>
---
 lib/igt_drm_stub.c | 125 +++++++++++++++++++++++++++++++++++++++++++++
 lib/meson.build    |   9 ++++
 2 files changed, 134 insertions(+)
 create mode 100644 lib/igt_drm_stub.c

diff --git a/lib/igt_drm_stub.c b/lib/igt_drm_stub.c
new file mode 100644
index 000000000..58395b329
--- /dev/null
+++ b/lib/igt_drm_stub.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2026 Intel Corporation
+ */
+
+/*
+ * Minimal DRM/PCI stubs for tools that need driver detection and device
+ * opening but do not link the full libigt.so. Requires libdrm and pciaccess.
+ *
+ * This reimplements a small subset of lib/drmtest.c (__drm_open_driver()),
+ * lib/igt_device.c (is_i915_device(), is_intel_device()) and
+ * lib/xe/xe_query.c (xe_dev_id()) so that tools can pull in just this
+ * static sub-library instead of the whole libigt.so stack.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <pciaccess.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+#include <unistd.h>
+#include <xf86drm.h>
+
+#include "drmtest.h"
+
+int igt_pci_system_init(void)
+{
+	return pci_system_init();
+}
+
+static bool driver_name_matches(int fd, const char *name)
+{
+	drmVersionPtr version;
+	bool match = false;
+
+	version = drmGetVersion(fd);
+	if (!version)
+		return false;
+
+	match = version->name_len > 0 && !strcmp(version->name, name);
+	drmFreeVersion(version);
+
+	return match;
+}
+
+bool is_i915_device(int fd)
+{
+	return driver_name_matches(fd, "i915");
+}
+
+bool is_intel_device(int fd)
+{
+	return is_i915_device(fd) || driver_name_matches(fd, "xe");
+}
+
+static uint16_t read_pci_device_id(int fd)
+{
+	char path[PATH_MAX], buf[32];
+	struct stat st;
+	int sysfs, len;
+	unsigned int devid;
+
+	if (fstat(fd, &st) || !S_ISCHR(st.st_mode))
+		return 0;
+
+	snprintf(path, sizeof(path), "/sys/dev/char/%d:%d/device/device",
+		 major(st.st_rdev), minor(st.st_rdev));
+	sysfs = open(path, O_RDONLY);
+	if (sysfs < 0)
+		return 0;
+
+	len = read(sysfs, buf, sizeof(buf) - 1);
+	close(sysfs);
+	if (len <= 0)
+		return 0;
+
+	buf[len] = '\0';
+	if (sscanf(buf, "0x%x", &devid) != 1)
+		return 0;
+
+	return devid;
+}
+
+/*
+ * Forward declaration required: xe_dev_id() is declared in the (heavy)
+ * lib/xe/xe_query.h, which this file intentionally does not include. The
+ * declaration below keeps -Wmissing-prototypes happy for the definition
+ * that follows.
+ */
+uint16_t xe_dev_id(int fd);
+uint16_t xe_dev_id(int fd)
+{
+	return read_pci_device_id(fd);
+}
+
+/* Maximum /dev/dri/card<N> minor number probed by __drm_open_driver(). */
+#define IGT_DRM_STUB_MAX_CARDS 16
+
+int __drm_open_driver(int chipset)
+{
+	char path[PATH_MAX];
+	int fd;
+
+	for (int i = 0; i < IGT_DRM_STUB_MAX_CARDS; i++) {
+		snprintf(path, sizeof(path), "/dev/dri/card%d", i);
+		fd = open(path, O_RDWR | O_CLOEXEC);
+		if (fd < 0)
+			continue;
+
+		if ((chipset == DRIVER_INTEL && is_i915_device(fd)) ||
+		    (chipset == DRIVER_XE && driver_name_matches(fd, "xe")) ||
+		    (chipset == DRIVER_ANY && is_intel_device(fd)))
+			return fd;
+
+		close(fd);
+	}
+
+	errno = ENODEV;
+	return -1;
+}
diff --git a/lib/meson.build b/lib/meson.build
index a57c1eb8d..484a912d7 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -356,6 +356,15 @@ lib_igt_tools_stub_build = static_library('igt_tools_stub',
 lib_igt_tools_stub = declare_dependency(link_with : lib_igt_tools_stub_build,
 					include_directories : inc)
 
+lib_igt_drm_stub_build = static_library('igt_drm_stub',
+	['igt_drm_stub.c'],
+	dependencies : [libdrm, pciaccess],
+	include_directories : inc)
+
+lib_igt_drm_stub = declare_dependency(link_with : lib_igt_drm_stub_build,
+				      dependencies : [libdrm, pciaccess],
+				      include_directories : inc)
+
 scan_dep = [
 	glib,
 	libpci,
-- 
2.53.0