metadata: get and set policies from go

This commit adds in the ability to get and set policy data from go using
the GetPolicy and SetPolicy functions. This is done via a patch of the
x/sys/unix package that exposes the filesystem encryption structures.

Note that not all the fields of the PolicyData protocol buffer are
needed to get and set policies. The wrapped_policy_keys are not used and
will be written and read by other components of fscrypt.

To run the policy tests, the environment variable BASE_TEST_DIR must be
set to a directory for testing on a filesystem that supports encryption.

Change-Id: I13b1d983356845f3ffc1945cedf53234218f32e5

1 files changed, 15 insertions, 0 deletions

diff --git a/util/errors.go b/util/errors.go
index aafeadd..bd63ac8 100644
--- a/util/errors.go
+++ b/util/errors.go
@@ -22,6 +22,7 @@ package util
 import (
 	"fmt"
 	"log"
+	"os"
 )
 
 // InvalidInputF creates an error that should indicate either bad input from a
@@ -48,3 +49,17 @@ func NeverError(err error) {
 		log.Panicf("NeverError() check failed: %v", err)
 	}
 }
+
+// UnderlyingError returns the underlying error for known os error types.
+// From: src/os/error.go
+func UnderlyingError(err error) error {
+	switch err := err.(type) {
+	case *os.PathError:
+		return err.Err
+	case *os.LinkError:
+		return err.Err
+	case *os.SyscallError:
+		return err.Err
+	}
+	return err
+}