actions: generate a config file for fscrypt

This commit adds in the actions package. This package will be the
highest-level interface to the fscrypt packages. The public functions
in this package will be called directly from cmd/fscrypt.

The actions added in this commit pertain to creating and reading the
fscrypt global config file "fscrypt.conf". The challenging part about
creating this file is finding the correct hashing parameters for the
desired time target.

The getHashingCosts() function finds the desired costs by doubling the
costs and running the passphrase hash until the target is exceeded.
Then, a cost estimate is obtained using a linear interpolation between
the last two costs (and their time results).

Change-Id: I4a0eaf4856ec4ff49eb4360da3267f7caa9d07b2

1 files changed, 97 insertions, 0 deletions

diff --git a/actions/context.go b/actions/context.go
new file mode 100644
index 0000000..f4a3985
--- /dev/null
+++ b/actions/context.go
@@ -0,0 +1,97 @@
+/*
+ * context.go - top-level interface to fscrypt packages
+ *
+ * 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 actions is the high-level interface to the fscrypt packages. The
+// functions here roughly correspond with commands for the tool in cmd/fscrypt.
+// All of the actions include a significant amount of logging, so that good
+// output can be provided for cmd/fscrypt's verbose mode.
+// The top-level actions currently include:
+//	- Creating a new config file
+//	- Creating a context on which to perform actions
+//	- Creating, unlocking, and modifying Protectors
+//	- Creating, unlocking, and modifying Policies
+package actions
+
+import (
+	"errors"
+	"fmt"
+	"log"
+
+	"fscrypt/filesystem"
+	"fscrypt/metadata"
+	"fscrypt/util"
+)
+
+// Errors relating to Config files or Config structures.
+var (
+	ErrNoConfigFile     = fmt.Errorf("config file %q does not exist", ConfigFileLocation)
+	ErrBadConfigFile    = fmt.Errorf("config file %q has invalid data", ConfigFileLocation)
+	ErrConfigFileExists = fmt.Errorf("config file %q already exists", ConfigFileLocation)
+	ErrBadConfig        = errors.New("invalid Config structure provided")
+)
+
+// Context contains the necessary global state to perform most of fscrypt's
+// actions. It contains a config struct, which is loaded from the global config
+// file, but can be edited manually. A context is specific to a filesystem, and
+// all actions to add, edit, remove, and apply Protectors and Policies are done
+// relative to that filesystem.
+type Context struct {
+	Config *metadata.Config
+	Mount  *filesystem.Mount
+}
+
+// NewContextFromPath makes a context for the filesystem containing the
+// specified path and whose Config is loaded from the global config file. On
+// success, the Context contains a valid Config and Mount.
+func NewContextFromPath(path string) (ctx *Context, err error) {
+	ctx = new(Context)
+
+	if ctx.Mount, err = filesystem.FindMount(path); err != nil {
+		err = util.UnderlyingError(err)
+		return
+	}
+
+	if ctx.Config, err = getConfig(); err != nil {
+		return
+	}
+
+	log.Printf("%s is on %s filesystem %q (%s)", path,
+		ctx.Mount.Filesystem, ctx.Mount.Path, ctx.Mount.Device)
+	return
+}
+
+// NewContextFromMountpoint makes a context for the filesystem at the specified
+// mountpoint and whose Config is loaded from the global config file. On
+// success, the Context contains a valid Config and Mount.
+func NewContextFromMountpoint(mountpoint string) (ctx *Context, err error) {
+	ctx = new(Context)
+
+	if ctx.Mount, err = filesystem.GetMount(mountpoint); err != nil {
+		err = util.UnderlyingError(err)
+		return
+	}
+
+	if ctx.Config, err = getConfig(); err != nil {
+		return
+	}
+
+	log.Printf("found %s filesystem %q (%s)", ctx.Mount.Filesystem,
+		ctx.Mount.Path, ctx.Mount.Device)
+	return
+}