NVMe: Dynamically allocate partition numbers

Some users need more than 64 partitions per device.  Rather than simply
increasing the number of partitions, switch to the dynamic partition
allocation scheme.

This means that minor numbers are not stable across boots, but since major
numbers aren't either, I cannot see this being a significant problem.
Tested-by: NMatias Bjørling <m@bjorling.me>
Signed-off-by: NMatthew Wilcox <matthew.r.wilcox@intel.com>

drivers/block/nvme-core.c

@@ -46,7 +46,6 @@
 #define NVME_Q_DEPTH 1024
 #define SQ_SIZE(depth)		(depth * sizeof(struct nvme_command))
 #define CQ_SIZE(depth)		(depth * sizeof(struct nvme_completion))
-#define NVME_MINORS 64
 #define ADMIN_TIMEOUT	(60 * HZ)
 
 static int nvme_major;
@@ -1780,33 +1779,6 @@ static int nvme_kthread(void *data)
 	return 0;
 }
 
-static DEFINE_IDA(nvme_index_ida);
-
-static int nvme_get_ns_idx(void)
-{
-	int index, error;
-
-	do {
-		if (!ida_pre_get(&nvme_index_ida, GFP_KERNEL))
-			return -1;
-
-		spin_lock(&dev_list_lock);
-		error = ida_get_new(&nvme_index_ida, &index);
-		spin_unlock(&dev_list_lock);
-	} while (error == -EAGAIN);
-
-	if (error)
-		index = -1;
-	return index;
-}
-
-static void nvme_put_ns_idx(int index)
-{
-	spin_lock(&dev_list_lock);
-	ida_remove(&nvme_index_ida, index);
-	spin_unlock(&dev_list_lock);
-}
-
 static void nvme_config_discard(struct nvme_ns *ns)
 {
 	u32 logical_block_size = queue_logical_block_size(ns->queue);
@@ -1840,7 +1812,7 @@ static struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, unsigned nsid,
 	ns->dev = dev;
 	ns->queue->queuedata = ns;
 
-	disk = alloc_disk(NVME_MINORS);
+	disk = alloc_disk(0);
 	if (!disk)
 		goto out_free_queue;
 	ns->ns_id = nsid;
@@ -1853,12 +1825,12 @@ static struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, unsigned nsid,
 		blk_queue_max_hw_sectors(ns->queue, dev->max_hw_sectors);
 
 	disk->major = nvme_major;
-	disk->minors = NVME_MINORS;
-	disk->first_minor = NVME_MINORS * nvme_get_ns_idx();
+	disk->first_minor = 0;
 	disk->fops = &nvme_fops;
 	disk->private_data = ns;
 	disk->queue = ns->queue;
 	disk->driverfs_dev = &dev->pci_dev->dev;
+	disk->flags = GENHD_FL_EXT_DEVT;
 	sprintf(disk->disk_name, "nvme%dn%d", dev->instance, nsid);
 	set_capacity(disk, le64_to_cpup(&id->nsze) << (ns->lba_shift - 9));
 
@@ -1876,9 +1848,7 @@ static struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, unsigned nsid,
 
 static void nvme_ns_free(struct nvme_ns *ns)
 {
-	int index = ns->disk->first_minor / NVME_MINORS;
 	put_disk(ns->disk);
-	nvme_put_ns_idx(index);
 	blk_cleanup_queue(ns->queue);
 	kfree(ns);
 }