unix: add support for Linux filesystem encryption

This CL adds in the necessary types and constants to support Linux
filesystem encryption. This includes the structs for the keys and
polices as well as the constants for key size and encryption algorithms.

This code also reduces the scope of some of the regexes in mkerrors.sh.
This is to reduce the number of unrelated constants added in with this
change.

Note that due to a bug in the Linux uapi headers, not all of the
necessary constants and structures are declared in linux/fs.h despite
being part of the kernel ABI. This means that some constants and types
had to be manually added in.

The bug has been patched (https://patchwork.kernel.org/patch/9662723),
and the manual additions can be removed when the patch is merged into
the mainline kernel.

Change-Id: Ib508ad99bdf4c0068933ffcf351c52bb359cfcf4
Reviewed-on: https://go-review.googlesource.com/41417
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/linux/types.go

@@ -56,6 +56,7 @@ package unix
 #include <utime.h>
 #include <linux/can.h>
 #include <linux/if_alg.h>
+#include <linux/fs.h>
 #include <linux/vm_sockets.h>
 
 // On mips64, the glibc stat and kernel stat do not agree
@@ -107,6 +108,14 @@ struct stat {
 
 #endif
 
+// Certain constants and structs are missing from the fs/crypto UAPI
+#define FS_MAX_KEY_SIZE                 64
+struct fscrypt_key {
+  __u32 mode;
+  __u8 raw[FS_MAX_KEY_SIZE];
+  __u32 size;
+};
+
 #ifdef TCSETS2
 // On systems that have "struct termios2" use this as type Termios.
 typedef struct termios2 termios_t;
@@ -248,6 +257,12 @@ type Fsid C.fsid_t
 
 type Flock_t C.struct_flock
 
+// Filesystem Encryption
+
+type FscryptPolicy C.struct_fscrypt_policy
+
+type FscryptKey C.struct_fscrypt_key
+
 // Advice to Fadvise
 
 const (