Move CreateLdsoconfdFile to ContainerRoot

Since the creation of a .conf file in /etc/ld.so.conf.d is shared by
both the update-ldcache and enable-cuda-compat hooks, this is moved
to the ContainerRoot type.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/oci/container-root.go

@@ -18,6 +18,7 @@
 package oci
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -28,6 +29,48 @@ import (
 // A ContainerRoot represents the root directory of a container's filesystem.
 type ContainerRoot string
 
+// CreateLdsoconfdFile creates a file at /etc/ld.so.conf.d/ in the specified container root.
+// The file is created at /etc/ld.so.conf.d/{{ .pattern }} using `CreateTemp` and
+// contains the specified directories on each line.
+func (r ContainerRoot) CreateLdsoconfdFile(pattern string, dirs ...string) error {
+	if len(dirs) == 0 {
+		return nil
+	}
+
+	ldsoconfdDir, err := r.Resolve("/etc/ld.so.conf.d")
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(ldsoconfdDir, 0755); err != nil {
+		return fmt.Errorf("failed to create ld.so.conf.d: %w", err)
+	}
+
+	configFile, err := os.CreateTemp(ldsoconfdDir, pattern)
+	if err != nil {
+		return fmt.Errorf("failed to create config file: %w", err)
+	}
+	defer configFile.Close()
+
+	added := make(map[string]bool)
+	for _, dir := range dirs {
+		if added[dir] {
+			continue
+		}
+		_, err = configFile.WriteString(fmt.Sprintf("%s\n", dir))
+		if err != nil {
+			return fmt.Errorf("failed to update config file: %w", err)
+		}
+		added[dir] = true
+	}
+
+	// The created file needs to be world readable for the cases where the container is run as a non-root user.
+	if err := configFile.Chmod(0644); err != nil {
+		return fmt.Errorf("failed to chmod config file: %w", err)
+	}
+
+	return nil
+}
+
 // GlobFiles matches the specified pattern in the container root.
 // The files that match must be regular files. Symlinks and directories are ignored.
 func (r ContainerRoot) GlobFiles(pattern string) ([]string, error) {

internal/oci/container-root_test.go

@@ -0,0 +1,66 @@
+/**
+# Copyright (c) 2025, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+**/
+
+package oci
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestUpdateLdconfig(t *testing.T) {
+	testCases := []struct {
+		description      string
+		folders          []string
+		expectedContents string
+	}{
+		{
+			description: "no folders; have no contents",
+		},
+		{
+			description:      "single folder is added",
+			folders:          []string{"/usr/local/cuda/compat"},
+			expectedContents: "/usr/local/cuda/compat\n",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.description, func(t *testing.T) {
+			containerRootDir := t.TempDir()
+			c := ContainerRoot(containerRootDir)
+			err := c.CreateLdsoconfdFile("00-test-*.conf", tc.folders...)
+			require.NoError(t, err)
+
+			matches, err := filepath.Glob(filepath.Join(containerRootDir, "/etc/ld.so.conf.d/00-test-*.conf"))
+			require.NoError(t, err)
+
+			if tc.expectedContents == "" {
+				require.Empty(t, matches)
+				return
+			}
+
+			require.Len(t, matches, 1)
+			contents, err := os.ReadFile(matches[0])
+			require.NoError(t, err)
+
+			require.EqualValues(t, tc.expectedContents, string(contents))
+		})
+	}
+
+}