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 <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 42bd1cb7c9cd..583ac81669c2 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -60,14 +60,14 @@ static struct inode *anon_inode_make_secure_inode(
 	const struct inode *context_inode)
 {
 	struct inode *inode;
-	const struct qstr qname = QSTR_INIT(name, strlen(name));
 	int error;
 
 	inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
 	if (IS_ERR(inode))
 		return inode;
 	inode->i_flags &= ~S_PRIVATE;
-	error =	security_inode_init_security_anon(inode, &qname, context_inode);
+	error =	security_inode_init_security_anon(inode, &QSTR(name),
+						  context_inode);
 	if (error) {
 		iput(inode);
 		return ERR_PTR(error);