vfs: make it possible to access the dentry hash/len as one 64-bit entry

This allows comparing hash and len in one operation on 64-bit
architectures.  Right now only __d_lookup_rcu() takes advantage of this,
since that is the case we care most about.

The use of anonymous struct/unions hides the alternate 64-bit approach
from most users, the exception being a few cases where we initialize a
'struct qstr' with a static initializer.  This makes the problematic
cases use a new QSTR_INIT() helper function for that (but initializing
just the name pointer with a "{ .name = xyzzy }" initializer remains
valid, as does just copying another qstr structure).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/ubifs/tnc.c b/fs/ubifs/tnc.c
index 16ad84d..abd5133 100644
--- a/fs/ubifs/tnc.c
+++ b/fs/ubifs/tnc.c
@@ -2361,7 +2361,7 @@
 			 * by passing 'ubifs_tnc_remove_nm()' the same key but
 			 * an unmatchable name.
 			 */
-			struct qstr noname = { .len = 0, .name = "" };
+			struct qstr noname = { .name = "" };
 
 			err = dbg_check_tnc(c, 0);
 			mutex_unlock(&c->tnc_mutex);