Handle case where symlink already exists in create-symlinks hook

Signed-off-by: Christopher Desiniotis <cdesiniotis@nvidia.com>

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

@@ -17,6 +17,7 @@
 package symlinks
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -25,6 +26,7 @@ import (
 	"github.com/urfave/cli/v2"
 
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/logger"
+	"github.com/NVIDIA/nvidia-container-toolkit/internal/lookup/symlinks"
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/oci"
 )
 
@@ -121,8 +123,17 @@ func (m command) run(c *cli.Context, cfg *config) error {
 func (m command) createLink(containerRoot string, targetPath string, link string) error {
 	linkPath := filepath.Join(containerRoot, link)
 
+	exists, err := doesLinkExist(targetPath, linkPath)
+	if err != nil {
+		return fmt.Errorf("failed to check if link exists: %w", err)
+	}
+	if exists {
+		m.logger.Debugf("Link %s already exists", linkPath)
+		return nil
+	}
+
 	m.logger.Infof("Symlinking %v to %v", linkPath, targetPath)
-	err := os.MkdirAll(filepath.Dir(linkPath), 0755)
+	err = os.MkdirAll(filepath.Dir(linkPath), 0755)
 	if err != nil {
 		return fmt.Errorf("failed to create directory: %v", err)
 	}
@@ -133,3 +144,19 @@ func (m command) createLink(containerRoot string, targetPath string, link string
 
 	return nil
 }
+
+// doesLinkExist returns true if link exists and points to target.
+// An error is returned if link exists but points to a different target.
+func doesLinkExist(target string, link string) (bool, error) {
+	currentTarget, err := symlinks.Resolve(link)
+	if errors.Is(err, os.ErrNotExist) {
+		return false, nil
+	}
+	if err != nil {
+		return false, fmt.Errorf("failed to resolve existing symlink %s: %w", link, err)
+	}
+	if currentTarget == target {
+		return true, nil
+	}
+	return true, fmt.Errorf("unexpected link target: %s", currentTarget)
+}

cmd/nvidia-cdi-hook/create-symlinks/create-symlinks_test.go

@@ -12,6 +12,36 @@ import (
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/lookup/symlinks"
 )
 
+func TestDoesLinkExist(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	require.NoError(
+		t,
+		makeFs(tmpDir,
+			dirOrLink{path: "/a/b/c", target: "d"},
+			dirOrLink{path: "/a/b/e", target: "/a/b/f"},
+		),
+	)
+
+	exists, err := doesLinkExist("d", filepath.Join(tmpDir, "/a/b/c"))
+	require.NoError(t, err)
+	require.True(t, exists)
+
+	exists, err = doesLinkExist("/a/b/f", filepath.Join(tmpDir, "/a/b/e"))
+	require.NoError(t, err)
+	require.True(t, exists)
+
+	_, err = doesLinkExist("different-target", filepath.Join(tmpDir, "/a/b/c"))
+	require.Error(t, err)
+
+	_, err = doesLinkExist("/a/b/d", filepath.Join(tmpDir, "/a/b/c"))
+	require.Error(t, err)
+
+	exists, err = doesLinkExist("foo", filepath.Join(tmpDir, "/a/b/does-not-exist"))
+	require.NoError(t, err)
+	require.False(t, exists)
+}
+
 func TestCreateLinkRelativePath(t *testing.T) {
 	tmpDir := t.TempDir()
 	hostRoot := filepath.Join(tmpDir, "/host-root/")
@@ -56,12 +86,28 @@ func TestCreateLinkAlreadyExists(t *testing.T) {
 
 	// nvidia-cdi-hook create-symlinks --link libfoo.so.1::/lib/libfoo.so
 	err := getTestCommand().createLink(containerRoot, "libfoo.so.1", "/lib/libfoo.so")
-	require.Error(t, err)
+	require.NoError(t, err)
 	target, err := symlinks.Resolve(filepath.Join(containerRoot, "lib/libfoo.so"))
 	require.NoError(t, err)
 	require.Equal(t, "libfoo.so.1", target)
 }
 
+func TestCreateLinkAlreadyExistsDifferentTarget(t *testing.T) {
+	tmpDir := t.TempDir()
+	hostRoot := filepath.Join(tmpDir, "/host-root/")
+	containerRoot := filepath.Join(tmpDir, "/container-root")
+
+	require.NoError(t, makeFs(hostRoot))
+	require.NoError(t, makeFs(containerRoot, dirOrLink{path: "/lib/libfoo.so", target: "different-target"}))
+
+	// nvidia-cdi-hook create-symlinks --link libfoo.so.1::/lib/libfoo.so
+	err := getTestCommand().createLink(containerRoot, "libfoo.so.1", "/lib/libfoo.so")
+	require.Error(t, err)
+	target, err := symlinks.Resolve(filepath.Join(containerRoot, "lib/libfoo.so"))
+	require.NoError(t, err)
+	require.Equal(t, "different-target", target)
+}
+
 type dirOrLink struct {
 	path   string
 	target string