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-rw-r--r--include/linux/idr.h1
-rw-r--r--lib/idr.c13
2 files changed, 14 insertions, 0 deletions
diff --git a/include/linux/idr.h b/include/linux/idr.h
index 43b87b1c77a3..7b1c5c6f9a06 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 d66e75bfc1a0..5cd602936645 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -60,6 +60,16 @@ static int idr_max(int layers)
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 @@ static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa,
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 @@ build_up:
* upwards.
*/
p->layer++;
+ WARN_ON_ONCE(p->prefix);
continue;
}
if (!(new = idr_layer_alloc(gfp_mask, layer_idr))) {
@@ -334,6 +346,7 @@ build_up:
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;

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