ida: simplified functions for id allocation

The current hyper-optimized functions are overkill if you simply want to
allocate an id for a device.  Create versions which use an internal
lock.

In followup patches, numerous drivers are converted to use this
interface.

Thanks to Tejun for feedback.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/idr.h

@@ -146,6 +146,10 @@ void ida_remove(struct ida *ida, int id);
 void ida_destroy(struct ida *ida);
 void ida_init(struct ida *ida);
 
+int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
+		   gfp_t gfp_mask);
+void ida_simple_remove(struct ida *ida, unsigned int id);
+
 void __init idr_init_cache(void);
 
 #endif /* __IDR_H__ */

lib/idr.c

@@ -34,8 +34,10 @@
 #include <linux/err.h>
 #include <linux/string.h>
 #include <linux/idr.h>
+#include <linux/spinlock.h>
 
 static struct kmem_cache *idr_layer_cache;
+static DEFINE_SPINLOCK(simple_ida_lock);
 
 static struct idr_layer *get_from_free_list(struct idr *idp)
 {
@@ -925,6 +927,71 @@ void ida_destroy(struct ida *ida)
 }
 EXPORT_SYMBOL(ida_destroy);
 
+/**
+ * ida_simple_get - get a new id.
+ * @ida: the (initialized) ida.
+ * @start: the minimum id (inclusive, < 0x8000000)
+ * @end: the maximum id (exclusive, < 0x8000000 or 0)
+ * @gfp_mask: memory allocation flags
+ *
+ * Allocates an id in the range start <= id < end, or returns -ENOSPC.
+ * On memory allocation failure, returns -ENOMEM.
+ *
+ * Use ida_simple_remove() to get rid of an id.
+ */
+int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
+		   gfp_t gfp_mask)
+{
+	int ret, id;
+	unsigned int max;
+
+	BUG_ON((int)start < 0);
+	BUG_ON((int)end < 0);
+
+	if (end == 0)
+		max = 0x80000000;
+	else {
+		BUG_ON(end < start);
+		max = end - 1;
+	}
+
+again:
+	if (!ida_pre_get(ida, gfp_mask))
+		return -ENOMEM;
+
+	spin_lock(&simple_ida_lock);
+	ret = ida_get_new_above(ida, start, &id);
+	if (!ret) {
+		if (id > max) {
+			ida_remove(ida, id);
+			ret = -ENOSPC;
+		} else {
+			ret = id;
+		}
+	}
+	spin_unlock(&simple_ida_lock);
+
+	if (unlikely(ret == -EAGAIN))
+		goto again;
+
+	return ret;
+}
+EXPORT_SYMBOL(ida_simple_get);
+
+/**
+ * ida_simple_remove - remove an allocated id.
+ * @ida: the (initialized) ida.
+ * @id: the id returned by ida_simple_get.
+ */
+void ida_simple_remove(struct ida *ida, unsigned int id)
+{
+	BUG_ON((int)id < 0);
+	spin_lock(&simple_ida_lock);
+	ida_remove(ida, id);
+	spin_unlock(&simple_ida_lock);
+}
+EXPORT_SYMBOL(ida_simple_remove);
+
 /**
  * ida_init - initialize ida handle
  * @ida:	ida handle