+/**
+ * idr_preload - preload for idr_alloc()
+ * @gfp_mask: allocation mask to use for preloading
+ *
+ * Preload per-cpu layer buffer for idr_alloc(). Can only be used from
+ * process context and each idr_preload() invocation should be matched with
+ * idr_preload_end(). Note that preemption is disabled while preloaded.
+ *
+ * The first idr_alloc() in the preloaded section can be treated as if it
+ * were invoked with @gfp_mask used for preloading. This allows using more
+ * permissive allocation masks for idrs protected by spinlocks.
+ *
+ * For example, if idr_alloc() below fails, the failure can be treated as
+ * if idr_alloc() were called with GFP_KERNEL rather than GFP_NOWAIT.
+ *
+ * idr_preload(GFP_KERNEL);
+ * spin_lock(lock);
+ *
+ * id = idr_alloc(idr, ptr, start, end, GFP_NOWAIT);
+ *
+ * spin_unlock(lock);
+ * idr_preload_end();
+ * if (id < 0)
+ * error;
+ */
+void idr_preload(gfp_t gfp_mask)
+{
+ /*
+ * Consuming preload buffer from non-process context breaks preload
+ * allocation guarantee. Disallow usage from those contexts.
+ */
+ WARN_ON_ONCE(in_interrupt());
+ might_sleep_if(gfp_mask & __GFP_WAIT);
+
+ preempt_disable();
+
+ /*
+ * idr_alloc() is likely to succeed w/o full idr_layer buffer and
+ * return value from idr_alloc() needs to be checked for failure
+ * anyway. Silently give up if allocation fails. The caller can
+ * treat failures from idr_alloc() as if idr_alloc() were called
+ * with @gfp_mask which should be enough.
+ */
+ while (__this_cpu_read(idr_preload_cnt) < MAX_IDR_FREE) {
+ struct idr_layer *new;
+
+ preempt_enable();
+ new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
+ preempt_disable();
+ if (!new)
+ break;
+
+ /* link the new one to per-cpu preload list */
+ new->ary[0] = __this_cpu_read(idr_preload_head);
+ __this_cpu_write(idr_preload_head, new);
+ __this_cpu_inc(idr_preload_cnt);
+ }
+}
+EXPORT_SYMBOL(idr_preload);
+
+/**
+ * idr_alloc - allocate new idr entry
+ * @idr: the (initialized) idr
+ * @ptr: pointer to be associated with the new id
+ * @start: the minimum id (inclusive)
+ * @end: the maximum id (exclusive, <= 0 for max)
+ * @gfp_mask: memory allocation flags
+ *
+ * Allocate an id in [start, end) and associate it with @ptr. If no ID is
+ * available in the specified range, returns -ENOSPC. On memory allocation
+ * failure, returns -ENOMEM.
+ *
+ * Note that @end is treated as max when <= 0. This is to always allow
+ * using @start + N as @end as long as N is inside integer range.
+ *
+ * The user is responsible for exclusively synchronizing all operations
+ * which may modify @idr. However, read-only accesses such as idr_find()
+ * or iteration can be performed under RCU read lock provided the user
+ * destroys @ptr in RCU-safe way after removal from idr.
+ */
+int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask)
+{
+ int max = end > 0 ? end - 1 : INT_MAX; /* inclusive upper limit */
+ struct idr_layer *pa[MAX_IDR_LEVEL];
+ int id;
+
+ might_sleep_if(gfp_mask & __GFP_WAIT);
+
+ /* sanity checks */
+ if (WARN_ON_ONCE(start < 0))
+ return -EINVAL;
+ if (unlikely(max < start))
+ return -ENOSPC;
+
+ /* allocate id */
+ id = idr_get_empty_slot(idr, start, pa, gfp_mask, NULL);
+ if (unlikely(id < 0))
+ return id;
+ if (unlikely(id > max))
+ return -ENOSPC;
+
+ idr_fill_slot(ptr, id, pa);
+ return id;
+}
+EXPORT_SYMBOL_GPL(idr_alloc);
+