Add symlinks package with Resolve function

This change adds a symlinks.Resolve function for resolving symlinks and
updates usages across the code to make use of it.

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

cmd/nvidia-ctk/hook/create-symlinks/create-symlinks.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/discover/csv"
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/lookup"
+	"github.com/NVIDIA/nvidia-container-toolkit/internal/lookup/symlinks"
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/oci"
 	"github.com/sirupsen/logrus"
 	"github.com/urfave/cli/v2"
@@ -125,21 +126,18 @@ func (m command) run(c *cli.Context, cfg *config) error {
 	created := make(map[string]bool)
 	// candidates is a list of absolute paths to symlinks in a chain, or the final target of the chain.
 	for _, candidate := range candidates {
-		targets, err := m.Locate(candidate)
+		target, err := symlinks.Resolve(candidate)
 		if err != nil {
 			m.logger.Debugf("Skipping invalid link: %v", err)
 			continue
-		} else if len(targets) != 1 {
-			m.logger.Debugf("Unexepected number of targets: %v", targets)
-			continue
-		} else if targets[0] == candidate {
+		} else if target == candidate {
 			m.logger.Debugf("%v is not a symlink", candidate)
 			continue
 		}
 
-		err = m.createLink(created, cfg.hostRoot, containerRoot, targets[0], candidate)
+		err = m.createLink(created, cfg.hostRoot, containerRoot, target, candidate)
 		if err != nil {
-			m.logger.Warnf("Failed to create link %v: %v", []string{targets[0], candidate}, err)
+			m.logger.Warnf("Failed to create link %v: %v", []string{target, candidate}, err)
 		}
 	}
 

internal/ldcache/ldcache.go

@@ -29,6 +29,7 @@ import (
 	"syscall"
 	"unsafe"
 
+	"github.com/NVIDIA/nvidia-container-toolkit/internal/lookup/symlinks"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -288,16 +289,7 @@ func (c *ldcache) resolve(target string) (string, error) {
 
 	c.logger.Debugf("checking %v", string(name))
 
-	info, err := os.Lstat(name)
-	if err != nil {
-		return "", fmt.Errorf("failed to get file info: %v", info)
-	}
-	if info.Mode()&os.ModeSymlink == 0 {
-		c.logger.Debugf("Resolved regular file: %v", name)
-		return name, nil
-	}
-
-	link, err := os.Readlink(name)
+	link, err := symlinks.Resolve(name)
 	if err != nil {
 		return "", fmt.Errorf("failed to resolve symlink: %v", err)
 	}

internal/lookup/symlinks.go

@@ -18,9 +18,9 @@ package lookup
 
 import (
 	"fmt"
-	"os"
 	"path/filepath"
 
+	"github.com/NVIDIA/nvidia-container-toolkit/internal/lookup/symlinks"
 	"github.com/sirupsen/logrus"
 )
 
@@ -74,16 +74,9 @@ func (p symlinkChain) Locate(pattern string) ([]string, error) {
 		}
 		found[candidate] = true
 
-		info, err := os.Lstat(candidate)
+		target, err := symlinks.Resolve(candidate)
 		if err != nil {
-			return nil, fmt.Errorf("failed to get file info: %v", info)
-		}
-		if info.Mode()&os.ModeSymlink == 0 {
-			continue
-		}
-		target, err := os.Readlink(candidate)
-		if err != nil {
-			return nil, fmt.Errorf("error checking symlink: %v", err)
+			return nil, fmt.Errorf("error resolving symlink: %v", err)
 		}
 
 		if !filepath.IsAbs(target) {

internal/lookup/symlinks/symlink.go

@@ -0,0 +1,35 @@
+/**
+# Copyright (c) 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 symlinks
+
+import (
+	"fmt"
+	"os"
+)
+
+// Resolve returns the link target of the specified filename or the filename if it is not a link.
+func Resolve(filename string) (string, error) {
+	info, err := os.Lstat(filename)
+	if err != nil {
+		return filename, fmt.Errorf("failed to get file info: %v", info)
+	}
+	if info.Mode()&os.ModeSymlink == 0 {
+		return filename, nil
+	}
+
+	return os.Readlink(filename)
+}