fuse: return correct dentry for ->mkdir

fuse already uses d_splice_alias() to ensure an appropriate dentry is
found for a newly created dentry.  Now that ->mkdir can return that
dentry we do so.

This requires changing create_new_entry() to return a dentry and
handling that change in all callers.

Note that when create_new_entry() is asked to create anything other than
a directory we can be sure it will NOT return an alternate dentry as
d_splice_alias() only returns an alternate dentry for directories.
So we don't need to check for that case when passing one the result.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/174112490070.33508.15852253149143067890@noble.neil.brown.name
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: neilbrown

fs/fuse/dir.c

@@ -781,9 +781,9 @@ static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
 /*
  * Code shared between mknod, mkdir, symlink and link
  */
-static int create_new_entry(struct mnt_idmap *idmap, struct fuse_mount *fm,
-			    struct fuse_args *args, struct inode *dir,
-			    struct dentry *entry, umode_t mode)
+static struct dentry *create_new_entry(struct mnt_idmap *idmap, struct fuse_mount *fm,
+				       struct fuse_args *args, struct inode *dir,
+				       struct dentry *entry, umode_t mode)
 {
 	struct fuse_entry_out outarg;
 	struct inode *inode;
@@ -792,11 +792,11 @@ static int create_new_entry(struct mnt_idmap *idmap, struct fuse_mount *fm,
 	struct fuse_forget_link *forget;
 
 	if (fuse_is_bad(dir))
-		return -EIO;
+		return ERR_PTR(-EIO);
 
 	forget = fuse_alloc_forget();
 	if (!forget)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	memset(&outarg, 0, sizeof(outarg));
 	args->nodeid = get_node_id(dir);
@@ -826,29 +826,43 @@ static int create_new_entry(struct mnt_idmap *idmap, struct fuse_mount *fm,
 			  &outarg.attr, ATTR_TIMEOUT(&outarg), 0, 0);
 	if (!inode) {
 		fuse_queue_forget(fm->fc, forget, outarg.nodeid, 1);
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 	}
 	kfree(forget);
 
 	d_drop(entry);
 	d = d_splice_alias(inode, entry);
 	if (IS_ERR(d))
-		return PTR_ERR(d);
+		return d;
 
-	if (d) {
+	if (d)
 		fuse_change_entry_timeout(d, &outarg);
-		dput(d);
-	} else {
+	else
 		fuse_change_entry_timeout(entry, &outarg);
-	}
 	fuse_dir_changed(dir);
-	return 0;
+	return d;
 
  out_put_forget_req:
 	if (err == -EEXIST)
 		fuse_invalidate_entry(entry);
 	kfree(forget);
-	return err;
+	return ERR_PTR(err);
+}
+
+static int create_new_nondir(struct mnt_idmap *idmap, struct fuse_mount *fm,
+			     struct fuse_args *args, struct inode *dir,
+			     struct dentry *entry, umode_t mode)
+{
+	/*
+	 * Note that when creating anything other than a directory we
+	 * can be sure create_new_entry() will NOT return an alternate
+	 * dentry as d_splice_alias() only returns an alternate dentry
+	 * for directories.  So we don't need to check for that case
+	 * when passing back the result.
+	 */
+	WARN_ON_ONCE(S_ISDIR(mode));
+
+	return PTR_ERR(create_new_entry(idmap, fm, args, dir, entry, mode));
 }
 
 static int fuse_mknod(struct mnt_idmap *idmap, struct inode *dir,
@@ -871,7 +885,7 @@ static int fuse_mknod(struct mnt_idmap *idmap, struct inode *dir,
 	args.in_args[0].value = &inarg;
 	args.in_args[1].size = entry->d_name.len + 1;
 	args.in_args[1].value = entry->d_name.name;
-	return create_new_entry(idmap, fm, &args, dir, entry, mode);
+	return create_new_nondir(idmap, fm, &args, dir, entry, mode);
 }
 
 static int fuse_create(struct mnt_idmap *idmap, struct inode *dir,
@@ -917,7 +931,7 @@ static struct dentry *fuse_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	args.in_args[0].value = &inarg;
 	args.in_args[1].size = entry->d_name.len + 1;
 	args.in_args[1].value = entry->d_name.name;
-	return ERR_PTR(create_new_entry(idmap, fm, &args, dir, entry, S_IFDIR));
+	return create_new_entry(idmap, fm, &args, dir, entry, S_IFDIR);
 }
 
 static int fuse_symlink(struct mnt_idmap *idmap, struct inode *dir,
@@ -934,7 +948,7 @@ static int fuse_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	args.in_args[1].value = entry->d_name.name;
 	args.in_args[2].size = len;
 	args.in_args[2].value = link;
-	return create_new_entry(idmap, fm, &args, dir, entry, S_IFLNK);
+	return create_new_nondir(idmap, fm, &args, dir, entry, S_IFLNK);
 }
 
 void fuse_flush_time_update(struct inode *inode)
@@ -1131,7 +1145,7 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
 	args.in_args[0].value = &inarg;
 	args.in_args[1].size = newent->d_name.len + 1;
 	args.in_args[1].value = newent->d_name.name;
-	err = create_new_entry(&invalid_mnt_idmap, fm, &args, newdir, newent, inode->i_mode);
+	err = create_new_nondir(&invalid_mnt_idmap, fm, &args, newdir, newent, inode->i_mode);
 	if (!err)
 		fuse_update_ctime_in_cache(inode);
 	else if (err == -EINTR)