[PATCH RFC v2 02/16] fs: add fput_close_list() and fput_list()

[Christian Brauner <brauner@kernel.org>]

Add helpers for paths that close many files in one go. They collect the
last references during the walk and drain them right after

fput_list() runs the final __fput() for everything on the list.
delayed_fput() shares that loop.

We'll use that in the next patches.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/file_table.c | 25 +++++++++++++++++++++----
 fs/internal.h   |  3 +++
 fs/open.c       |  2 +-
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index c68b8c0a4097..617912ca4e0a 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -528,11 +528,10 @@ static void __fput(struct file *file)
 static LLIST_HEAD(delayed_fput_list);
 static void delayed_fput(struct work_struct *unused)
 {
-	struct llist_node *node = llist_del_all(&delayed_fput_list);
-	struct file *f, *t;
+	/* Detach the shared list once, then drain it like a private one. */
+	struct llist_head list = { .first = llist_del_all(&delayed_fput_list) };
 
-	llist_for_each_entry_safe(f, t, node, f_llist)
-		__fput(f);
+	fput_list(&list);
 }
 
 static void ____fput(struct callback_head *work)
@@ -629,6 +628,24 @@ void fput_close(struct file *file)
 		__fput_deferred(file);
 }
 
+/* Like fput_close(), but the last reference goes on the caller's @list. */
+void fput_close_list(struct file *file, struct llist_head *list)
+{
+	if (file_ref_put_close(&file->f_ref))
+		__llist_add(&file->f_llist, list);
+}
+
+/* Run the final __fput() for everything on the private @list, right here. */
+void fput_list(struct llist_head *list)
+{
+	struct file *f, *t;
+
+	llist_for_each_entry_safe(f, t, __llist_del_all(list), f_llist) {
+		__fput(f);
+		cond_resched();
+	}
+}
+
 void __init files_init(void)
 {
 	struct kmem_cache_args args = {
diff --git a/fs/internal.h b/fs/internal.h
index c658c8a5ebd5..619eaeb23fd9 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -129,6 +129,8 @@ static inline void put_file_access(struct file *file)
 
 void fput_close_sync(struct file *);
 void fput_close(struct file *);
+void fput_close_list(struct file *file, struct llist_head *list);
+void fput_list(struct llist_head *list);
 
 /*
  * super.c
@@ -198,6 +200,7 @@ extern struct file *do_file_open_root(const struct path *,
 extern struct open_how build_open_how(int flags, umode_t mode);
 extern int build_open_flags(const struct open_how *how, struct open_flags *op);
 struct file *file_close_fd_locked(struct files_struct *files, unsigned fd);
+int filp_flush(struct file *filp, fl_owner_t id);
 
 int do_ftruncate(struct file *file, loff_t length, unsigned int flags);
 int chmod_common(const struct path *path, umode_t mode);
diff --git a/fs/open.c b/fs/open.c
index 6b1c14e684a9..7181665c3af5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1506,7 +1506,7 @@ SYSCALL_DEFINE2(creat, const char __user *, pathname, umode_t, mode)
  * "id" is the POSIX thread ID. We use the
  * files pointer for this..
  */
-static int filp_flush(struct file *filp, fl_owner_t id)
+int filp_flush(struct file *filp, fl_owner_t id)
 {
 	int retval = 0;
 

-- 
2.53.0