lib: add idr_remove_all

Remove all ids from the given idr tree.  idr_destroy() only frees up
unused, cached idp_layers, but this function will remove all id mappings
and leave all idp_layers unused.

A typical clean-up sequence for objects stored in an idr tree, will use
idr_for_each() to free all objects, if necessay, then idr_remove_all() to
remove all ids, and idr_destroy() to free up the cached idr_layers.

Signed-off-by: Kristian Hoegsberg <krh@redhat.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Dave Airlie <airlied@linux.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/idr.h

@@ -82,6 +82,7 @@ int idr_for_each(struct idr *idp,
 		 int (*fn)(int id, void *p, void *data), void *data);
 void *idr_replace(struct idr *idp, void *ptr, int id);
 void idr_remove(struct idr *idp, int id);
+void idr_remove_all(struct idr *idp);
 void idr_destroy(struct idr *idp);
 void idr_init(struct idr *idp);
 

lib/idr.c

@@ -390,6 +390,53 @@ void idr_remove(struct idr *idp, int id)
 }
 EXPORT_SYMBOL(idr_remove);
 
+/**
+ * idr_remove_all - remove all ids from the given idr tree
+ * @idp: idr handle
+ *
+ * idr_destroy() only frees up unused, cached idp_layers, but this
+ * function will remove all id mappings and leave all idp_layers
+ * unused.
+ *
+ * A typical clean-up sequence for objects stored in an idr tree, will
+ * use idr_for_each() to free all objects, if necessay, then
+ * idr_remove_all() to remove all ids, and idr_destroy() to free
+ * up the cached idr_layers.
+ */
+void idr_remove_all(struct idr *idp)
+{
+	int n, id, max, error = 0;
+	struct idr_layer *p;
+	struct idr_layer *pa[MAX_LEVEL];
+	struct idr_layer **paa = &pa[0];
+
+	n = idp->layers * IDR_BITS;
+	p = idp->top;
+	max = 1 << n;
+
+	id = 0;
+	while (id < max && !error) {
+		while (n > IDR_BITS && p) {
+			n -= IDR_BITS;
+			*paa++ = p;
+			p = p->ary[(id >> n) & IDR_MASK];
+		}
+
+		id += 1 << n;
+		while (n < fls(id)) {
+			if (p) {
+				memset(p, 0, sizeof *p);
+				free_layer(idp, p);
+			}
+			n += IDR_BITS;
+			p = *--paa;
+		}
+	}
+	idp->top = NULL;
+	idp->layers = 0;
+}
+EXPORT_SYMBOL(idr_remove_all);
+
 /**
  * idr_destroy - release all cached layers within an idr tree
  * idp: idr handle