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>

7 files changed, 6 insertions, 12 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);
diff --git a/fs/bcachefs/fsck.c b/fs/bcachefs/fsck.c
index 75c8a97a6954..7b3b63ed747c 100644
--- a/fs/bcachefs/fsck.c
+++ b/fs/bcachefs/fsck.c
@@ -405,7 +405,7 @@ static int reattach_inode(struct btree_trans *trans, struct bch_inode_unpacked *
 		return ret;
 
 	struct bch_hash_info dir_hash = bch2_hash_info_init(c, &lostfound);
-	struct qstr name = (struct qstr) QSTR(name_buf);
+	struct qstr name = QSTR(name_buf);
 
 	inode->bi_dir = lostfound.bi_inum;
 
diff --git a/fs/bcachefs/recovery.c b/fs/bcachefs/recovery.c
index 3c7f941dde39..ebabba296882 100644
--- a/fs/bcachefs/recovery.c
+++ b/fs/bcachefs/recovery.c
@@ -32,8 +32,6 @@
 #include <linux/sort.h>
 #include <linux/stat.h>
 
-#define QSTR(n) { { { .len = strlen(n) } }, .name = n }
-
 void bch2_btree_lost_data(struct bch_fs *c, enum btree_id btree)
 {
 	if (btree >= BTREE_ID_NR_MAX)
diff --git a/fs/bcachefs/util.h b/fs/bcachefs/util.h
index fb02c1c36004..a27f4b84fe77 100644
--- a/fs/bcachefs/util.h
+++ b/fs/bcachefs/util.h
@@ -647,8 +647,6 @@ static inline int cmp_le32(__le32 l, __le32 r)
 
 #include <linux/uuid.h>
 
-#define QSTR(n) { { { .len = strlen(n) } }, .name = n }
-
 static inline bool qstr_eq(const struct qstr l, const struct qstr r)
 {
 	return l.len == r.len && !memcmp(l.name, r.name, l.len);
diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
index a90d7d649739..60d2cf26e837 100644
--- a/fs/erofs/xattr.c
+++ b/fs/erofs/xattr.c
@@ -407,7 +407,7 @@ int erofs_getxattr(struct inode *inode, int index, const char *name,
 	}
 
 	it.index = index;
-	it.name = (struct qstr)QSTR_INIT(name, strlen(name));
+	it.name = QSTR(name);
 	if (it.name.len > EROFS_NAME_LEN)
 		return -ERANGE;
 
diff --git a/fs/file_table.c b/fs/file_table.c
index 976736be47cb..a329623d0b42 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -351,9 +351,7 @@ static struct file *alloc_file(const struct path *path, int flags,
 static inline int alloc_path_pseudo(const char *name, struct inode *inode,
 				    struct vfsmount *mnt, struct path *path)
 {
-	struct qstr this = QSTR_INIT(name, strlen(name));
-
-	path->dentry = d_alloc_pseudo(mnt->mnt_sb, &this);
+	path->dentry = d_alloc_pseudo(mnt->mnt_sb, &QSTR(name));
 	if (!path->dentry)
 		return -ENOMEM;
 	path->mnt = mntget(mnt);
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8502ef68459b..0eb320617d7b 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -927,7 +927,7 @@ repeat:
 		if (!inode)
 			continue;
 
-		name = (struct qstr)QSTR_INIT(kn->name, strlen(kn->name));
+		name = QSTR(kn->name);
 		parent = kernfs_get_parent(kn);
 		if (parent) {
 			p_inode = ilookup(info->sb, kernfs_ino(parent));