Add locators for symlinks and character devices

This change adds a symlink locator that follows symlinks and returns all
elements in the chain and a device locator that finds character devices.

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

internal/lookup/device.go

@@ -0,0 +1,53 @@
+/**
+# Copyright (c) 2021, 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 lookup
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/sirupsen/logrus"
+)
+
+const (
+	devRoot = "/dev"
+)
+
+// NewCharDeviceLocator creates a Locator that can be used to find char devices at the specified root. A logger is
+// also specified.
+func NewCharDeviceLocator(logger *logrus.Logger, root string) Locator {
+	l := file{
+		logger:   logger,
+		prefixes: []string{root, filepath.Join(root, devRoot)},
+		filter:   assertCharDevice,
+	}
+
+	return &l
+}
+
+// assertCharDevice checks whether the specified path is a char device and returns an error if this is not the case.
+func assertCharDevice(filename string) error {
+	info, err := os.Stat(filename)
+	if err != nil {
+		return fmt.Errorf("error getting info: %v", err)
+	}
+	if info.Mode()|os.ModeCharDevice == 0 {
+		return fmt.Errorf("%v is not a char device", filename)
+	}
+	return nil
+}

internal/lookup/dir.go

@@ -0,0 +1,50 @@
+/*
+# Copyright (c) 2021, 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 lookup
+
+import (
+	"fmt"
+	"os"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// NewDirectoryLocator creates a Locator that can be used to find directories at the specified root. A logger
+// is also specified.
+func NewDirectoryLocator(logger *log.Logger, root string) Locator {
+	l := file{
+		logger:   logger,
+		prefixes: []string{root},
+		filter:   assertDirectory,
+	}
+
+	return &l
+}
+
+// assertDirectory checks wither the specified path is a directory.
+func assertDirectory(filename string) error {
+	info, err := os.Stat(filename)
+	if err != nil {
+		return fmt.Errorf("error getting info for %v: %v", filename, err)
+	}
+
+	if !info.IsDir() {
+		return fmt.Errorf("specified path '%v' is not a directory", filename)
+	}
+
+	return nil
+}

internal/lookup/symlinks.go

@@ -0,0 +1,123 @@
+/**
+# Copyright (c) 2021, 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 lookup
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/sirupsen/logrus"
+)
+
+type symlinkChain struct {
+	file
+}
+
+type symlink struct {
+	file
+}
+
+// NewSymlinkChainLocator creats a locator that can be used for locating files through symlinks.
+// A logger can also be specified.
+func NewSymlinkChainLocator(logger *logrus.Logger, root string) Locator {
+	l := symlinkChain{
+		file: newFileLocator(logger, root),
+	}
+
+	return &l
+}
+
+// NewSymlinkLocator creats a locator that can be used for locating files through symlinks.
+// A logger can also be specified.
+func NewSymlinkLocator(logger *logrus.Logger, root string) Locator {
+	l := symlink{
+		file: newFileLocator(logger, root),
+	}
+
+	return &l
+}
+
+// Locate finds the specified file at the specified root. If the file is a symlink, the link is followed and all candidates
+// to the final target are returned.
+func (p symlinkChain) Locate(filename string) ([]string, error) {
+	candidates, err := p.file.Locate(filename)
+	if err != nil {
+		return nil, err
+	}
+	if len(candidates) == 0 {
+		return candidates, nil
+	}
+
+	found := make(map[string]bool)
+	for len(candidates) > 0 {
+		candidate := candidates[0]
+		candidates = candidates[:len(candidates)-1]
+		if found[candidate] {
+			continue
+		}
+		found[candidate] = true
+
+		info, err := os.Lstat(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)
+		}
+
+		if !filepath.IsAbs(target) {
+			target, err = filepath.Abs(filepath.Join(filepath.Dir(candidate), target))
+			if err != nil {
+				return nil, fmt.Errorf("failed to construct absolute path: %v", err)
+			}
+		}
+
+		p.logger.Debugf("Resolved link: '%v' => '%v'", candidate, target)
+		if !found[target] {
+			candidates = append(candidates, target)
+		}
+	}
+
+	var filenames []string
+	for f := range found {
+		filenames = append(filenames, f)
+	}
+	return filenames, nil
+}
+
+// Locate finds the specified file at the specified root. If the file is a symlink, the link is resolved and the target returned.
+func (p symlink) Locate(filename string) ([]string, error) {
+	candidates, err := p.file.Locate(filename)
+	if err != nil {
+		return nil, err
+	}
+	if len(candidates) != 1 {
+		return nil, fmt.Errorf("failed to uniquely resolve symlink %v: %v", filename, candidates)
+	}
+
+	target, err := filepath.EvalSymlinks(candidates[0])
+	if err != nil {
+		return nil, fmt.Errorf("failed to resolve link: %v", err)
+	}
+
+	return []string{target}, err
+}