[PATCH] configfs: Convenience macros for attribute definition.

Sysfs has the _ATTR() and _ATTR_RO() macros to make defining extended
form attributes easier.  configfs should have something similiar.

- _CONFIGFS_ATTR() and _CONFIGFS_ATTR_RO() are the counterparts to the
  sysfs macros.
- CONFIGFS_ATTR_STRUCT() creates the extended form attribute structure.
- CONFIGFS_ATTR_OPS() defines the show_attribute()/store_attribute()
  operations that call the show()/store() operations of the extended
  form configfs_attributes.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

1 files changed, 65 insertions, 2 deletions

diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 0a5491baf0bc..7f627775c947 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -130,8 +130,25 @@ struct configfs_attribute {
 /*
  * Users often need to create attribute structures for their configurable
  * attributes, containing a configfs_attribute member and function pointers
- * for the show() and store() operations on that attribute. They can use
- * this macro (similar to sysfs' __ATTR) to make defining attributes easier.
+ * for the show() and store() operations on that attribute. If they don't
+ * need anything else on the extended attribute structure, they can use
+ * this macro to define it  The argument _item is the name of the
+ * config_item structure.
+ */
+#define CONFIGFS_ATTR_STRUCT(_item)                                     \
+struct _item##_attribute {                                              \
+        struct configfs_attribute attr;                                 \
+        ssize_t (*show)(struct _item *, char *);                        \
+        ssize_t (*store)(struct _item *, const char *, size_t);         \
+}
+
+/*
+ * With the extended attribute structure, users can use this macro
+ * (similar to sysfs' __ATTR) to make defining attributes easier.
+ * An example:
+ * #define MYITEM_ATTR(_name, _mode, _show, _store)     \
+ * struct myitem_attribute childless_attr_##_name =     \
+ *         __CONFIGFS_ATTR(_name, _mode, _show, _store)
  */
 #define __CONFIGFS_ATTR(_name, _mode, _show, _store)                    \
 {                                                                       \
@@ -143,6 +160,52 @@ struct configfs_attribute {
         .show   = _show,                                                \
         .store  = _store,                                               \
 }
+/* Here is a readonly version, only requiring a show() operation */
+#define __CONFIGFS_ATTR_RO(_name, _show)                                \
+{                                                                       \
+        .attr   = {                                                     \
+                        .ca_name = __stringify(_name),                  \
+                        .ca_mode = 0444,                                \
+                        .ca_owner = THIS_MODULE,                        \
+        },                                                              \
+        .show   = _show,                                                \
+}
+
+/*
+ * With these extended attributes, the simple show_attribute() and
+ * store_attribute() operations need to call the show() and store() of the
+ * attributes.  This is a common pattern, so we provide a macro to define
+ * them.  The argument _item is the name of the config_item structure.
+ * This macro expects the attributes to be named "struct <name>_attribute"
+ * and the function to_<name>() to exist;
+ */
+#define CONFIGFS_ATTR_OPS(_item)                                        \
+static ssize_t _item##_attr_show(struct config_item *item,              \
+                                 struct configfs_attribute *attr,       \
+                                 char *page)                            \
+{                                                                       \
+        struct _item *_item = to_##_item(item);                         \
+        struct _item##_attribute *_item##_attr =                        \
+                container_of(attr, struct _item##_attribute, attr);     \
+        ssize_t ret = 0;                                                \
+                                                                        \
+        if (_item##_attr->show)                                         \
+                ret = _item##_attr->show(_item, page);                  \
+        return ret;                                                     \
+}                                                                       \
+static ssize_t _item##_attr_store(struct config_item *item,             \
+                                  struct configfs_attribute *attr,      \
+                                  const char *page, size_t count)       \
+{                                                                       \
+        struct _item *_item = to_##_item(item);                         \
+        struct _item##_attribute *_item##_attr =                        \
+                container_of(attr, struct _item##_attribute, attr);     \
+        ssize_t ret = -EINVAL;                                          \
+                                                                        \
+        if (_item##_attr->store)                                        \
+                ret = _item##_attr->store(_item, page, count);          \
+        return ret;                                                     \
+}
 
 /*
  * If allow_link() exists, the item can symlink(2) out to other