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idr: add idr_layer->prefix

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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>
This commit is contained in:
Tejun Heo 2013-02-27 17:05:07 -08:00 committed by Linus Torvalds
parent 050a6b47d9
commit 54616283c2
2 changed files with 14 additions and 0 deletions
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1
include/linux/idr.h
View File

@ -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 */

13
lib/idr.c
View File

@ -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 @@ static int idr_get_empty_slot(struct idr *idp, int starting_id,
* upwards.
*/
p->layer++;
WARN_ON_ONCE(p->prefix);
continue;
}
if (!(new = idr_layer_alloc(gfp_mask, layer_idr))) {
@ -334,6 +346,7 @@ static int idr_get_empty_slot(struct idr *idp, int starting_id,
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;