filesystem: creating the directories and files

This commit adds in the filesystem subpackage. The goal of this package
is to provide and interface for adding to and removing from the metadata
storage for a given filesystem. This is primarily done in filesystem.go.
To facilitate this functionality, mountpoint.go exposes an interface for
querying the system about the current mounted filesystems and their
information. Note that this operation is done with a lazy loading
mechanism.

To refer to other filesystems, we use link files that can be parsed by
libblkid. The README is also updated to account for this new dependancy.

This package uses the FSError type under the hood so that error messages
will include the filesystem name, but callers can still check for
specific error instances.

Change-Id: I74fe4e84b8e3a5b73f1337c35307ffe0bf7cdea9

1 files changed, 83 insertions, 0 deletions

diff --git a/filesystem/path.go b/filesystem/path.go
new file mode 100644
index 0000000..3be1859
--- /dev/null
+++ b/filesystem/path.go
@@ -0,0 +1,83 @@
+/*
+ * path.go - Utility functions for dealing with filesystem paths
+ *
+ * Copyright 2017 Google Inc.
+ * Author: Joe Richey (joerichey@google.com)
+ *
+ * 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 filesystem
+
+import (
+	"log"
+	"os"
+	"path/filepath"
+)
+
+// We only check the unix permissions and the sticky bit
+const permMask = os.ModeSticky | os.ModePerm
+
+// cannonicalizePath turns path into an absolute path without symlinks.
+func cannonicalizePath(path string) (string, error) {
+	path, err := filepath.Abs(path)
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.EvalSymlinks(path)
+}
+
+// loggedStat runs os.Stat, but it logs the error if stat returns any error
+// other than nil or IsNotExist.
+func loggedStat(name string) (os.FileInfo, error) {
+	info, err := os.Stat(name)
+	if err != nil && !os.IsNotExist(err) {
+		log.Print(err)
+	}
+	return info, err
+}
+
+// isDir returns true if the path exists and is that of a directory.
+func isDir(path string) bool {
+	info, err := loggedStat(path)
+	return err == nil && info.IsDir()
+}
+
+// isDevice returns true if the path exists and is that of a directory.
+func isDevice(path string) bool {
+	info, err := loggedStat(path)
+	return err == nil && info.Mode()&os.ModeDevice != 0
+}
+
+// isDirCheckPerm returns true if the path exists and is a directory. If the
+// specified permissions and sticky bit of mode do not match the path, and error
+// is logged.
+func isDirCheckPerm(path string, mode os.FileMode) bool {
+	info, err := loggedStat(path)
+	// Check if directory
+	if err != nil || !info.IsDir() {
+		return false
+	}
+	// Check for bad permissions
+	if info.Mode()&permMask != mode&permMask {
+		log.Printf("directory %s has incorrect permissions", path)
+	}
+	return true
+}
+
+// isRegularFile returns true if the path exists and is that of a regular file.
+func isRegularFile(path string) bool {
+	info, err := loggedStat(path)
+	return err == nil && info.Mode().IsRegular()
+}