idr: add idr_layer->prefix
Add a field which carries the prefix of ID the idr_layer covers. This
will be used to implement lookup hint.
This patch doesn't make use of the new field and doesn't introduce any
behavior difference.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/idr.h b/include/linux/idr.h
index 43b87b1..7b1c5c6 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -28,6 +28,7 @@
#define IDR_MASK ((1 << IDR_BITS)-1)
struct idr_layer {
+ int prefix; /* the ID prefix of this idr_layer */
DECLARE_BITMAP(bitmap, IDR_SIZE); /* A zero bit means "space here" */
struct idr_layer __rcu *ary[1<<IDR_BITS];
int count; /* When zero, we can release it */
diff --git a/lib/idr.c b/lib/idr.c
index d66e75b..5cd6029 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -60,6 +60,16 @@
return (1 << bits) - 1;
}
+/*
+ * Prefix mask for an idr_layer at @layer. For layer 0, the prefix mask is
+ * all bits except for the lower IDR_BITS. For layer 1, 2 * IDR_BITS, and
+ * so on.
+ */
+static int idr_layer_prefix_mask(int layer)
+{
+ return ~idr_max(layer + 1);
+}
+
static struct idr_layer *get_from_free_list(struct idr *idp)
{
struct idr_layer *p;
@@ -272,6 +282,7 @@
if (!new)
return -ENOMEM;
new->layer = l-1;
+ new->prefix = id & idr_layer_prefix_mask(new->layer);
rcu_assign_pointer(p->ary[m], new);
p->count++;
}
@@ -313,6 +324,7 @@
* upwards.
*/
p->layer++;
+ WARN_ON_ONCE(p->prefix);
continue;
}
if (!(new = idr_layer_alloc(gfp_mask, layer_idr))) {
@@ -334,6 +346,7 @@
new->ary[0] = p;
new->count = 1;
new->layer = layers-1;
+ new->prefix = id & idr_layer_prefix_mask(new->layer);
if (bitmap_full(p->bitmap, IDR_SIZE))
__set_bit(0, new->bitmap);
p = new;