vfio: selftests: Move helper to get cdev path to libvfio

Move the helper function to get the VFIO cdev path to libvfio so that it
can be used in libvfio in a subsequent commit.

No functional change intended.

Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20250822212518.4156428-24-dmatlack@google.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

tools/testing/selftests/vfio/lib/include/vfio_util.h

@@ -175,6 +175,7 @@ struct vfio_pci_device {
  * If BDF cannot be determined then the test will exit with KSFT_SKIP.
  */
 const char *vfio_selftests_get_bdf(int *argc, char *argv[]);
+const char *vfio_pci_get_cdev_path(const char *bdf);
 
 struct vfio_pci_device *vfio_pci_device_init(const char *bdf, int iommu_type);
 void vfio_pci_device_cleanup(struct vfio_pci_device *device);

tools/testing/selftests/vfio/lib/vfio_pci_device.c

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-only
+#include <dirent.h>
 #include <fcntl.h>
 #include <libgen.h>
 #include <stdlib.h>
@@ -332,6 +333,36 @@ static void vfio_pci_device_setup(struct vfio_pci_device *device, const char *bd
 		device->msi_eventfds[i] = -1;
 }
 
+const char *vfio_pci_get_cdev_path(const char *bdf)
+{
+	char dir_path[PATH_MAX];
+	struct dirent *entry;
+	char *cdev_path;
+	DIR *dir;
+
+	cdev_path = calloc(PATH_MAX, 1);
+	VFIO_ASSERT_NOT_NULL(cdev_path);
+
+	snprintf(dir_path, sizeof(dir_path), "/sys/bus/pci/devices/%s/vfio-dev/", bdf);
+
+	dir = opendir(dir_path);
+	VFIO_ASSERT_NOT_NULL(dir, "Failed to open directory %s\n", dir_path);
+
+	while ((entry = readdir(dir)) != NULL) {
+		/* Find the file that starts with "vfio" */
+		if (strncmp("vfio", entry->d_name, 4))
+			continue;
+
+		snprintf(cdev_path, PATH_MAX, "/dev/vfio/devices/%s", entry->d_name);
+		break;
+	}
+
+	VFIO_ASSERT_NE(cdev_path[0], 0, "Failed to find vfio cdev file.\n");
+	VFIO_ASSERT_EQ(closedir(dir), 0);
+
+	return cdev_path;
+}
+
 struct vfio_pci_device *vfio_pci_device_init(const char *bdf, int iommu_type)
 {
 	struct vfio_pci_device *device;

tools/testing/selftests/vfio/vfio_iommufd_setup_test.c

@@ -1,8 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#include <assert.h>
-#include <dirent.h>
-#include <fcntl.h>
-
 #include <uapi/linux/types.h>
 #include <linux/limits.h>
 #include <linux/sizes.h>
@@ -11,7 +7,6 @@
 
 #include <stdint.h>
 #include <stdio.h>
-#include <string.h>
 #include <sys/ioctl.h>
 #include <unistd.h>
 
@@ -19,32 +14,7 @@
 #include "../kselftest_harness.h"
 
 static const char iommu_dev_path[] = "/dev/iommu";
-static char cdev_path[PATH_MAX] = { '\0' };
+static const char *cdev_path;
-
-static void set_cdev_path(const char *bdf)
-{
-	char dir_path[PATH_MAX];
-	DIR *dir;
-	struct dirent *entry;
-
-	snprintf(dir_path, sizeof(dir_path), "/sys/bus/pci/devices/%s/vfio-dev/", bdf);
-
-	dir = opendir(dir_path);
-	assert(dir);
-
-	/* Find the file named "vfio<number>" */
-	while ((entry = readdir(dir)) != NULL) {
-		if (!strncmp("vfio", entry->d_name, 4)) {
-			snprintf(cdev_path, sizeof(cdev_path), "/dev/vfio/devices/%s",
-				 entry->d_name);
-			break;
-		}
-	}
-
-	assert(strlen(cdev_path) > 0);
-
-	closedir(dir);
-}
 
 static int vfio_device_bind_iommufd_ioctl(int cdev_fd, int iommufd)
 {
@@ -150,7 +120,7 @@ int main(int argc, char *argv[])
 {
 	const char *device_bdf = vfio_selftests_get_bdf(&argc, argv);
 
-	set_cdev_path(device_bdf);
+	cdev_path = vfio_pci_get_cdev_path(device_bdf);
 	printf("Using cdev device %s\n", cdev_path);
 
 	return test_harness_run(argc, argv);