[RESEND PATCH v4 12/15] fs/resctrl: Hide kmode_cpus[_list] on groups not bound to kernel-mode

[Babu Moger]

kmode_cpus and kmode_cpus_list describe the CPU scope for the rdtgroup that
owns the active kernel-mode binding. They are meaningful only for
resctrl_kcfg.k_rdtgrp.

On groups that do not own the kernel-mode binding, they appear as inactive
stubs and can let user space inspect or update state that does not apply to
that group.

Hide kmode_cpus and kmode_cpus_list on groups that are not bound to
kernel-mode. Keep the files hidden when groups are created, show them when
rdtgroup_config_kmode() binds the group, and hide them again when the
binding is released.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
v4: Updated the changelog and code comments.

v3: New patch to hide/show "kmode_cpus" and "kmode_cpus_list" when kernel
    modes binding changes.
---
 fs/resctrl/rdtgroup.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 413d3ff14546..c537846d9264 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1127,6 +1127,35 @@ static int resctrl_kernel_mode_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+/**
+ * resctrl_kmode_files_set_visible() - Toggle visibility of the per-group
+ *		kernel-mode CPU files under @rdtgrp.
+ * @rdtgrp:	Resctrl group whose "kmode_cpus" / "kmode_cpus_list" files
+ *		should be hidden or shown.
+ * @visible:	%true to expose the files, %false to hide them via
+ *		kernfs_show().
+ *
+ * Each file is resolved independently as a sibling under @rdtgrp->kn.
+ * Failures from kernfs_find_and_get() are deliberately ignored, allowing
+ * callers to invoke this before activation, during group creation, or when
+ * the kernel-mode binding is updated.
+ */
+static void resctrl_kmode_files_set_visible(struct rdtgroup *rdtgrp, bool visible)
+{
+	/* Keep in sync with res_common_files[] entries for these files. */
+	static const char * const files[] = { "kmode_cpus", "kmode_cpus_list" };
+	struct kernfs_node *kn;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(files); i++) {
+		kn = kernfs_find_and_get(rdtgrp->kn, files[i]);
+		if (!kn)
+			continue;
+		kernfs_show(kn, visible);
+		kernfs_put(kn);
+	}
+}
+
 /**
  * rdtgroup_config_kmode_reset() - Tear down the kernel-mode binding on @rdtgrp
  * @rdtgrp:	Resctrl group whose kernel-mode binding is being released.
@@ -1155,6 +1184,7 @@ static void rdtgroup_config_kmode_reset(struct rdtgroup *rdtgrp,
 
 out_clear:
 	cpumask_clear(&rdtgrp->kmode_cpu_mask);
+	resctrl_kmode_files_set_visible(rdtgrp, false);
 	rdtgrp->kmode = false;
 }
 
@@ -3068,6 +3098,7 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (ret)
 		goto out_closid_exit;
 
+	resctrl_kmode_files_set_visible(&rdtgroup_default, false);
 	kernfs_activate(rdtgroup_default.kn);
 
 	ret = rdtgroup_create_info_dir(rdtgroup_default.kn);
@@ -4098,6 +4129,7 @@ static int rdtgroup_mkdir_mon(struct kernfs_node *parent_kn,
 		goto out_unlock;
 	}
 
+	resctrl_kmode_files_set_visible(rdtgrp, false);
 	kernfs_activate(rdtgrp->kn);
 
 	/*
@@ -4142,6 +4174,7 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
 	if (ret)
 		goto out_closid_free;
 
+	resctrl_kmode_files_set_visible(rdtgrp, false);
 	kernfs_activate(rdtgrp->kn);
 
 	ret = rdtgroup_init_alloc(rdtgrp);
-- 
2.43.0