From 783bd07d095b722108725af11113795ee046ed0e Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sat, 27 Aug 2022 19:04:39 -1000 Subject: kernfs: Implement kernfs_show() Currently, kernfs nodes can be created hidden and activated later by calling kernfs_activate() to allow creation of multiple nodes to succeed or fail as a unit. This is an one-way one-time-only transition. This patch introduces kernfs_show() which can toggle visibility dynamically. As the currently proposed use - toggling the cgroup pressure files - only requires operating on leaf nodes, for the sake of simplicity, restrict it as such for now. Hiding uses the same mechanism as deactivation and likewise guarantees that there are no in-flight operations on completion. KERNFS_ACTIVATED and KERNFS_HIDDEN are used to manage the interactions between activations and show/hide operations. A node is visible iff both activated & !hidden. Cc: Chengming Zhou Cc: Johannes Weiner Tested-by: Chengming Zhou Reviewed-by: Chengming Zhou Signed-off-by: Tejun Heo Link: https://lore.kernel.org/r/20220828050440.734579-9-tj@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/kernfs/dir.c | 37 ++++++++++++++++++++++++++++++++++++- 1 file changed, 36 insertions(+), 1 deletion(-) (limited to 'fs/kernfs') diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index c9323956c63c..7fb5a72cc96d 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1311,7 +1311,7 @@ static void kernfs_activate_one(struct kernfs_node *kn) kn->flags |= KERNFS_ACTIVATED; - if (kernfs_active(kn) || (kn->flags & KERNFS_REMOVING)) + if (kernfs_active(kn) || (kn->flags & (KERNFS_HIDDEN | KERNFS_REMOVING))) return; WARN_ON_ONCE(kn->parent && RB_EMPTY_NODE(&kn->rb)); @@ -1347,6 +1347,41 @@ void kernfs_activate(struct kernfs_node *kn) up_write(&root->kernfs_rwsem); } +/** + * kernfs_show - show or hide a node + * @kn: kernfs_node to show or hide + * @show: whether to show or hide + * + * If @show is %false, @kn is marked hidden and deactivated. A hidden node is + * ignored in future activaitons. If %true, the mark is removed and activation + * state is restored. This function won't implicitly activate a new node in a + * %KERNFS_ROOT_CREATE_DEACTIVATED root which hasn't been activated yet. + * + * To avoid recursion complexities, directories aren't supported for now. + */ +void kernfs_show(struct kernfs_node *kn, bool show) +{ + struct kernfs_root *root = kernfs_root(kn); + + if (WARN_ON_ONCE(kernfs_type(kn) == KERNFS_DIR)) + return; + + down_write(&root->kernfs_rwsem); + + if (show) { + kn->flags &= ~KERNFS_HIDDEN; + if (kn->flags & KERNFS_ACTIVATED) + kernfs_activate_one(kn); + } else { + kn->flags |= KERNFS_HIDDEN; + if (kernfs_active(kn)) + atomic_add(KN_DEACTIVATED_BIAS, &kn->active); + kernfs_drain(kn); + } + + up_write(&root->kernfs_rwsem); +} + static void __kernfs_remove(struct kernfs_node *kn) { struct kernfs_node *pos; -- cgit v1.2.3