add a string-to-qstr constructor

Quite a few places want to build a struct qstr by given string;
it would be convenient to have a primitive doing that, rather
than open-coding it via QSTR_INIT().

The closest approximation was in bcachefs, but that expands to
initializer list - {.len = strlen(string), .name = string}.
It would be more useful to have it as compound literal -
(struct qstr){.len = strlen(string), .name = string}.

Unlike initializer list it's a valid expression.  What's more,
it's a valid lvalue - it's an equivalent of anonymous local
variable with such initializer, so the things like
	path->dentry = d_alloc_pseudo(mnt->mnt_sb, &QSTR(name));
are valid.  It can also be used as initializer, with identical
effect -
	struct qstr x = (struct qstr){.name = s, .len = strlen(s)};
is equivalent to
	struct qstr anon_variable = {.name = s, .len = strlen(s)};
	struct qstr x = anon_variable;
	// anon_variable is never used after that point
and any even remotely sane compiler will manage to collapse that
into
	struct qstr x = {.name = s, .len = strlen(s)};

What compound literals can't be used for is initialization of
global variables, but those are covered by QSTR_INIT().

This commit lifts definition(s) of QSTR() into linux/dcache.h,
converts it to compound literal (all bcachefs users are fine
with that) and converts assorted open-coded instances to using
that.

Signed-off-by: Al Viro <[email protected]>

1 files changed, 5 insertions, 9 deletions

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 7ce3721c06ca..eadc00410ebc 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -630,7 +630,7 @@ static int __rpc_rmpipe(struct inode *dir, struct dentry *dentry)
 static struct dentry *__rpc_lookup_create_exclusive(struct dentry *parent,
 					  const char *name)
 {
-	struct qstr q = QSTR_INIT(name, strlen(name));
+	struct qstr q = QSTR(name);
 	struct dentry *dentry = d_hash_and_lookup(parent, &q);
 	if (!dentry) {
 		dentry = d_alloc(parent, &q);
@@ -1190,8 +1190,7 @@ static const struct rpc_filelist files[] = {
 struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
 			       const unsigned char *dir_name)
 {
-	struct qstr dir = QSTR_INIT(dir_name, strlen(dir_name));
-	return d_hash_and_lookup(sb->s_root, &dir);
+	return d_hash_and_lookup(sb->s_root, &QSTR(dir_name));
 }
 EXPORT_SYMBOL_GPL(rpc_d_lookup_sb);
 
@@ -1300,11 +1299,9 @@ rpc_gssd_dummy_populate(struct dentry *root, struct rpc_pipe *pipe_data)
 	struct dentry *gssd_dentry;
 	struct dentry *clnt_dentry = NULL;
 	struct dentry *pipe_dentry = NULL;
-	struct qstr q = QSTR_INIT(files[RPCAUTH_gssd].name,
-				  strlen(files[RPCAUTH_gssd].name));
 
 	/* We should never get this far if "gssd" doesn't exist */
-	gssd_dentry = d_hash_and_lookup(root, &q);
+	gssd_dentry = d_hash_and_lookup(root, &QSTR(files[RPCAUTH_gssd].name));
 	if (!gssd_dentry)
 		return ERR_PTR(-ENOENT);
 
@@ -1314,9 +1311,8 @@ rpc_gssd_dummy_populate(struct dentry *root, struct rpc_pipe *pipe_data)
 		goto out;
 	}
 
-	q.name = gssd_dummy_clnt_dir[0].name;
-	q.len = strlen(gssd_dummy_clnt_dir[0].name);
-	clnt_dentry = d_hash_and_lookup(gssd_dentry, &q);
+	clnt_dentry = d_hash_and_lookup(gssd_dentry,
+					&QSTR(gssd_dummy_clnt_dir[0].name));
 	if (!clnt_dentry) {
 		__rpc_depopulate(gssd_dentry, gssd_dummy_clnt_dir, 0, 1);
 		pipe_dentry = ERR_PTR(-ENOENT);