scoutfs: add sysfs attrs wrappers

Add some helpers to manage the lifetime of groups of attributes in
sysfs.  We can wait until the sysfs files are no longer in use
before tearing down the data that they rely on.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/sysfs.c

@@ -103,6 +103,89 @@ static void kobj_del_put_wait(struct kobject *kobj, struct completion *comp)
 #define shutdown_kobj(sfinfo, _name) \
 	kobj_del_put_wait(&sfsinfo->_name##_kobj, &sfsinfo->_name##_comp)
 
+static void scoutfs_sysfs_release(struct kobject *kobj)
+{
+	DECLARE_SCOUTFS_SYSFS_ATTRS(ssa, kobj);
+
+	complete(&ssa->comp);
+}
+
+void scoutfs_sysfs_init_attrs(struct super_block *sb,
+			      struct scoutfs_sysfs_attrs *ssa)
+{
+	ssa->name = NULL;
+}
+
+/*
+ *  If this returns success then the file will be visible and show can
+ *  be called until unmount.
+ */
+int scoutfs_sysfs_create_attrs(struct super_block *sb,
+			       struct scoutfs_sysfs_attrs *ssa,
+			       struct attribute **attrs, char *fmt, ...)
+{
+	va_list args;
+	size_t name_len;
+	size_t size;
+	int ret;
+
+	/* ssa should have seen init or destroy */
+	if (WARN_ON_ONCE(ssa->name != NULL))
+		return -EINVAL;
+
+	ssa->sb = sb;
+	init_completion(&ssa->comp);
+	ssa->ktype.default_attrs = attrs;
+	ssa->ktype.sysfs_ops = &kobj_sysfs_ops;
+	ssa->ktype.release = scoutfs_sysfs_release;
+
+	va_start(args, fmt);
+	name_len = vsnprintf(NULL, 0, fmt, args);
+	va_end(args);
+	if (WARN_ON_ONCE(name_len < 1 || name_len > NAME_MAX)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	size = name_len + 1; /* with null */
+
+	ssa->name = kmalloc(size, GFP_KERNEL);
+	if (!ssa->name) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	va_start(args, fmt);
+	ret = vsnprintf(ssa->name, size, fmt, args);
+	va_end(args);
+	if (ret != name_len) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = kobject_init_and_add(&ssa->kobj, &ssa->ktype,
+				   scoutfs_sysfs_sb_dir(sb), "%s", ssa->name);
+out:
+	if (ret) {
+		kfree(ssa->name);
+		ssa->name = NULL;
+	}
+
+	return ret;
+}
+
+void scoutfs_sysfs_destroy_attrs(struct super_block *sb,
+				 struct scoutfs_sysfs_attrs *ssa)
+{
+	if (ssa->name) {
+		kobject_del(&ssa->kobj);
+		kobject_put(&ssa->kobj);
+		wait_for_completion(&ssa->comp);
+		kfree(ssa->name);
+		ssa->name = NULL;
+	}
+}
+
 /*
  * Only the return from kobj_init_and_add() tells us if the kobj needs
  * to be cleaned up or not.  This must manually clean up the kobjs and

kmod/src/sysfs.h

@@ -1,6 +1,43 @@
 #ifndef _SCOUTFS_SYSFS_H_
 #define _SCOUTFS_SYSFS_H_
 
+/*
+ * We have some light wrappers around sysfs attributes to make it safe
+ * to tear down the attributes before freeing the data they describe.
+ */
+
+#define SCOUTFS_ATTR_RO(_name)						\
+        static struct kobj_attribute scoutfs_attr_##_name = __ATTR_RO(_name)
+
+#define SCOUTFS_ATTR_PTR(_name)						\
+        &scoutfs_attr_##_name.attr
+
+struct scoutfs_sysfs_attrs {
+	struct super_block *sb;
+	char *name;
+	struct completion comp;
+
+	struct kobject kobj;
+	struct kobj_type ktype;
+};
+
+#define SCOUTFS_SYSFS_ATTRS(kobj)					\
+	container_of(kobj, struct scoutfs_sysfs_attrs, kobj)
+
+#define SCOUTFS_SYSFS_ATTRS_SB(kobj)					\
+	(SCOUTFS_SYSFS_ATTRS(kobj)->sb)
+
+#define DECLARE_SCOUTFS_SYSFS_ATTRS(name, kobj)				\
+	struct scoutfs_sysfs_attrs *ssa = SCOUTFS_SYSFS_ATTRS(kobj)
+
+void scoutfs_sysfs_init_attrs(struct super_block *sb,
+			      struct scoutfs_sysfs_attrs *ssa);
+int scoutfs_sysfs_create_attrs(struct super_block *sb,
+			       struct scoutfs_sysfs_attrs *ssa,
+			       struct attribute **attrs, char *fmt, ...);
+void scoutfs_sysfs_destroy_attrs(struct super_block *sb,
+				 struct scoutfs_sysfs_attrs *ssa);
+
 struct kobject *scoutfs_sysfs_sb_dir(struct super_block *sb);
 
 int scoutfs_setup_sysfs(struct super_block *sb);