NVMe: Use an IDA to allocate minor numbers

The current approach of using the namespace ID as the minor number
doesn't work when there are multiple adapters in the machine.  Rather
than statically partitioning the number of namespaces between adapters,
dynamically allocate minor numbers to namespaces as they are detected.
Signed-off-by: NMatthew Wilcox <matthew.r.wilcox@intel.com>

drivers/block/nvme.c

@@ -24,6 +24,7 @@
 #include <linux/errno.h>
 #include <linux/fs.h>
 #include <linux/genhd.h>
+#include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
@@ -1240,7 +1241,34 @@ static int nvme_kthread(void *data)
 	return 0;
 }
 
-static struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, int index,
+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 struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, int nsid,
 			struct nvme_id_ns *id, struct nvme_lba_range_type *rt)
 {
 	struct nvme_ns *ns;
@@ -1265,19 +1293,19 @@ static struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, int index,
 	disk = alloc_disk(NVME_MINORS);
 	if (!disk)
 		goto out_free_queue;
-	ns->ns_id = index;
+	ns->ns_id = nsid;
 	ns->disk = disk;
 	lbaf = id->flbas & 0xf;
 	ns->lba_shift = id->lbaf[lbaf].ds;
 
 	disk->major = nvme_major;
 	disk->minors = NVME_MINORS;
-	disk->first_minor = NVME_MINORS * index;
+	disk->first_minor = NVME_MINORS * nvme_get_ns_idx();
 	disk->fops = &nvme_fops;
 	disk->private_data = ns;
 	disk->queue = ns->queue;
 	disk->driverfs_dev = &dev->pci_dev->dev;
-	sprintf(disk->disk_name, "nvme%dn%d", dev->instance, index);
+	sprintf(disk->disk_name, "nvme%dn%d", dev->instance, nsid);
 	set_capacity(disk, le64_to_cpup(&id->nsze) << (ns->lba_shift - 9));
 
 	return ns;
@@ -1291,7 +1319,9 @@ static struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, int index,
 
 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);
 }