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>

fs/ubifs/xattr.c

@@ -298,7 +298,7 @@ int ubifs_setxattr(struct dentry *dentry, const char *name,
 {
 	struct inode *inode, *host = dentry->d_inode;
 	struct ubifs_info *c = host->i_sb->s_fs_info;
-	struct qstr nm = { .name = name, .len = strlen(name) };
+	struct qstr nm = QSTR_INIT(name, strlen(name));
 	struct ubifs_dent_node *xent;
 	union ubifs_key key;
 	int err, type;
@@ -361,7 +361,7 @@ ssize_t ubifs_getxattr(struct dentry *dentry, const char *name, void *buf,
 {
 	struct inode *inode, *host = dentry->d_inode;
 	struct ubifs_info *c = host->i_sb->s_fs_info;
-	struct qstr nm = { .name = name, .len = strlen(name) };
+	struct qstr nm = QSTR_INIT(name, strlen(name));
 	struct ubifs_inode *ui;
 	struct ubifs_dent_node *xent;
 	union ubifs_key key;
@@ -524,7 +524,7 @@ int ubifs_removexattr(struct dentry *dentry, const char *name)
 {
 	struct inode *inode, *host = dentry->d_inode;
 	struct ubifs_info *c = host->i_sb->s_fs_info;
-	struct qstr nm = { .name = name, .len = strlen(name) };
+	struct qstr nm = QSTR_INIT(name, strlen(name));
 	struct ubifs_dent_node *xent;
 	union ubifs_key key;
 	int err;