Move nvidia-ctk hook command into own binary

This change creates an nvidia-cdi-hook binary for implementing
CDI hooks. This allows for these hooks to be separated from the
nvidia-ctk command which may, for example, require libnvidia-ml
to support other functionality.

The nvidia-ctk hook subcommand is maintained as an alias for the
time being to allow for existing CDI specifications referring to
this path to work as expected.

Signed-off-by: Avi Deitcher <avi@deitcher.net>

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

@@ -0,0 +1,231 @@
+/**
+# Copyright (c) 2022, 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"
+	"path/filepath"
+	"strings"
+
+	"github.com/urfave/cli/v2"
+
+	"github.com/NVIDIA/nvidia-container-toolkit/internal/logger"
+	"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/NVIDIA/nvidia-container-toolkit/internal/platform-support/tegra/csv"
+)
+
+type command struct {
+	logger logger.Interface
+}
+
+type config struct {
+	hostRoot      string
+	filenames     cli.StringSlice
+	links         cli.StringSlice
+	containerSpec string
+}
+
+// NewCommand constructs a hook command with the specified logger
+func NewCommand(logger logger.Interface) *cli.Command {
+	c := command{
+		logger: logger,
+	}
+	return c.build()
+}
+
+// build
+func (m command) build() *cli.Command {
+	cfg := config{}
+
+	// Create the '' command
+	c := cli.Command{
+		Name:  "create-symlinks",
+		Usage: "A hook to create symlinks in the container. This can be used to process CSV mount specs",
+		Action: func(c *cli.Context) error {
+			return m.run(c, &cfg)
+		},
+	}
+
+	c.Flags = []cli.Flag{
+		&cli.StringFlag{
+			Name:        "host-root",
+			Usage:       "The root on the host filesystem to use to resolve symlinks",
+			Destination: &cfg.hostRoot,
+		},
+		&cli.StringSliceFlag{
+			Name:        "csv-filename",
+			Usage:       "Specify a (CSV) filename to process",
+			Destination: &cfg.filenames,
+		},
+		&cli.StringSliceFlag{
+			Name:        "link",
+			Usage:       "Specify a specific link to create. The link is specified as target::link",
+			Destination: &cfg.links,
+		},
+		&cli.StringFlag{
+			Name:        "container-spec",
+			Usage:       "Specify the path to the OCI container spec. If empty or '-' the spec will be read from STDIN",
+			Destination: &cfg.containerSpec,
+		},
+	}
+
+	return &c
+}
+
+func (m command) run(c *cli.Context, cfg *config) error {
+	s, err := oci.LoadContainerState(cfg.containerSpec)
+	if err != nil {
+		return fmt.Errorf("failed to load container state: %v", err)
+	}
+
+	containerRoot, err := s.GetContainerRoot()
+	if err != nil {
+		return fmt.Errorf("failed to determined container root: %v", err)
+	}
+
+	csvFiles := cfg.filenames.Value()
+
+	chainLocator := lookup.NewSymlinkChainLocator(
+		lookup.WithLogger(m.logger),
+		lookup.WithRoot(cfg.hostRoot),
+	)
+
+	var candidates []string
+	for _, file := range csvFiles {
+		mountSpecs, err := csv.NewCSVFileParser(m.logger, file).Parse()
+		if err != nil {
+			m.logger.Debugf("Skipping CSV file %v: %v", file, err)
+			continue
+		}
+
+		for _, ms := range mountSpecs {
+			if ms.Type != csv.MountSpecSym {
+				continue
+			}
+			targets, err := chainLocator.Locate(ms.Path)
+			if err != nil {
+				m.logger.Warningf("Failed to locate symlink %v", ms.Path)
+			}
+			candidates = append(candidates, targets...)
+		}
+	}
+
+	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 {
+		target, err := symlinks.Resolve(candidate)
+		if err != nil {
+			m.logger.Debugf("Skipping invalid link: %v", err)
+			continue
+		} else if target == candidate {
+			m.logger.Debugf("%v is not a symlink", candidate)
+			continue
+		}
+
+		err = m.createLink(created, cfg.hostRoot, containerRoot, target, candidate)
+		if err != nil {
+			m.logger.Warningf("Failed to create link %v: %v", []string{target, candidate}, err)
+		}
+	}
+
+	links := cfg.links.Value()
+	for _, l := range links {
+		parts := strings.Split(l, "::")
+		if len(parts) != 2 {
+			m.logger.Warningf("Invalid link specification %v", l)
+			continue
+		}
+
+		err := m.createLink(created, cfg.hostRoot, containerRoot, parts[0], parts[1])
+		if err != nil {
+			m.logger.Warningf("Failed to create link %v: %v", parts, err)
+		}
+	}
+
+	return nil
+
+}
+
+func (m command) createLink(created map[string]bool, hostRoot string, containerRoot string, target string, link string) error {
+	linkPath, err := changeRoot(hostRoot, containerRoot, link)
+	if err != nil {
+		m.logger.Warningf("Failed to resolve path for link %v relative to %v: %v", link, containerRoot, err)
+	}
+	if created[linkPath] {
+		m.logger.Debugf("Link %v already created", linkPath)
+		return nil
+	}
+
+	targetPath, err := changeRoot(hostRoot, "/", target)
+	if err != nil {
+		m.logger.Warningf("Failed to resolve path for target %v relative to %v: %v", target, "/", err)
+	}
+
+	m.logger.Infof("Symlinking %v to %v", linkPath, targetPath)
+	err = os.MkdirAll(filepath.Dir(linkPath), 0755)
+	if err != nil {
+		return fmt.Errorf("failed to create directory: %v", err)
+	}
+	err = os.Symlink(target, linkPath)
+	if err != nil {
+		return fmt.Errorf("failed to create symlink: %v", err)
+	}
+
+	return nil
+}
+
+func changeRoot(current string, new string, path string) (string, error) {
+	if !filepath.IsAbs(path) {
+		return path, nil
+	}
+
+	relative := path
+	if current != "" {
+		r, err := filepath.Rel(current, path)
+		if err != nil {
+			return "", err
+		}
+		relative = r
+	}
+
+	return filepath.Join(new, relative), nil
+}
+
+// Locate returns the link target of the specified filename or an empty slice if the
+// specified filename is not a symlink.
+func (m command) Locate(filename string) ([]string, error) {
+	info, err := os.Lstat(filename)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get file info: %v", info)
+	}
+	if info.Mode()&os.ModeSymlink == 0 {
+		m.logger.Debugf("%v is not a symlink", filename)
+		return nil, nil
+	}
+
+	target, err := os.Readlink(filename)
+	if err != nil {
+		return nil, fmt.Errorf("error checking symlink: %v", err)
+	}
+
+	m.logger.Debugf("Resolved link: '%v' => '%v'", filename, target)
+
+	return []string{target}, nil
+}