[svsm-devel] [PATCH v4 12/15] fs/configfs: Add a callback to determine attribute visibility

[Tom Lendacky]

In order to support dynamic decisions as to whether an attribute should be
created, add a callback that returns a bool to indicate whether the
attribute should be displayed. If no callback is registered, the attribute
is displayed by default.

Cc: Joel Becker <jlbec at evilplan.org>
Cc: Christoph Hellwig <hch at lst.de>
Co-developed-by: Dan Williams <dan.j.williams at intel.com>
Signed-off-by: Dan Williams <dan.j.williams at intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
---
 fs/configfs/dir.c        | 20 ++++++++++++++++++++
 include/linux/configfs.h |  3 +++
 2 files changed, 23 insertions(+)

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 18677cd4e62f..463e66258507 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -580,6 +580,7 @@ static void detach_attrs(struct config_item * item)
 static int populate_attrs(struct config_item *item)
 {
 	const struct config_item_type *t = item->ci_type;
+	struct configfs_group_operations *ops;
 	struct configfs_attribute *attr;
 	struct configfs_bin_attribute *bin_attr;
 	int error = 0;
@@ -587,14 +588,33 @@ static int populate_attrs(struct config_item *item)
 
 	if (!t)
 		return -EINVAL;
+
+	ops = t->ct_group_ops;
+	if (!ops) {
+		struct config_group *g = item->ci_group;
+
+		/*
+		 * No item specific group operations, check if the item's group
+		 * has group operations.
+		 */
+		if (g && g->cg_item.ci_type)
+			ops = g->cg_item.ci_type->ct_group_ops;
+	}
+
 	if (t->ct_attrs) {
 		for (i = 0; (attr = t->ct_attrs[i]) != NULL; i++) {
+			if (ops && ops->is_visible && !ops->is_visible(item, attr, i))
+				continue;
+
 			if ((error = configfs_create_file(item, attr)))
 				break;
 		}
 	}
 	if (t->ct_bin_attrs) {
 		for (i = 0; (bin_attr = t->ct_bin_attrs[i]) != NULL; i++) {
+			if (ops && ops->is_bin_visible && !ops->is_bin_visible(item, bin_attr, i))
+				continue;
+
 			error = configfs_create_bin_file(item, bin_attr);
 			if (error)
 				break;
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 2606711adb18..c771e9d0d0b9 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -216,6 +216,9 @@ struct configfs_group_operations {
 	struct config_group *(*make_group)(struct config_group *group, const char *name);
 	void (*disconnect_notify)(struct config_group *group, struct config_item *item);
 	void (*drop_item)(struct config_group *group, struct config_item *item);
+	bool (*is_visible)(struct config_item *item, struct configfs_attribute *attr, int n);
+	bool (*is_bin_visible)(struct config_item *item, struct configfs_bin_attribute *attr,
+			       int n);
 };
 
 struct configfs_subsystem {
-- 
2.43.2