block: refactor device number setup in __device_add_disk

Untangle the mess around blk_alloc_devt by moving the check for
the used allocation scheme into the callers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk.h

@@ -343,8 +343,8 @@ static inline void blk_queue_free_zone_bitmaps(struct request_queue *q) {}
 static inline void blk_queue_clear_zone_settings(struct request_queue *q) {}
 #endif
 
-int blk_alloc_devt(struct block_device *part, dev_t *devt);
-void blk_free_devt(dev_t devt);
+int blk_alloc_ext_minor(void);
+void blk_free_ext_minor(unsigned int minor);
 char *disk_name(struct gendisk *hd, int partno, char *buf);
 #define ADDPART_FLAG_NONE	0
 #define ADDPART_FLAG_RAID	1

block/genhd.c

@@ -333,52 +333,22 @@ static int blk_mangle_minor(int minor)
 	return minor;
 }
 
-/**
- * blk_alloc_devt - allocate a dev_t for a block device
- * @bdev: block device to allocate dev_t for
- * @devt: out parameter for resulting dev_t
- *
- * Allocate a dev_t for block device.
- *
- * RETURNS:
- * 0 on success, allocated dev_t is returned in *@devt.  -errno on
- * failure.
- *
- * CONTEXT:
- * Might sleep.
- */
-int blk_alloc_devt(struct block_device *bdev, dev_t *devt)
+int blk_alloc_ext_minor(void)
 {
-	struct gendisk *disk = bdev->bd_disk;
 	int idx;
 
-	/* in consecutive minor range? */
-	if (bdev->bd_partno < disk->minors) {
-		*devt = MKDEV(disk->major, disk->first_minor + bdev->bd_partno);
-		return 0;
-	}
-
 	idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT, GFP_KERNEL);
-	if (idx < 0)
-		return idx == -ENOSPC ? -EBUSY : idx;
-
-	*devt = MKDEV(BLOCK_EXT_MAJOR, blk_mangle_minor(idx));
-	return 0;
+	if (idx < 0) {
+		if (idx == -ENOSPC)
+			return -EBUSY;
+		return idx;
+	}
+	return blk_mangle_minor(idx);
 }
 
-/**
- * blk_free_devt - free a dev_t
- * @devt: dev_t to free
- *
- * Free @devt which was allocated using blk_alloc_devt().
- *
- * CONTEXT:
- * Might sleep.
- */
-void blk_free_devt(dev_t devt)
+void blk_free_ext_minor(unsigned int minor)
 {
-	if (MAJOR(devt) == BLOCK_EXT_MAJOR)
-		ida_free(&ext_devt_ida, blk_mangle_minor(MINOR(devt)));
+	ida_free(&ext_devt_ida, blk_mangle_minor(minor));
 }
 
 static char *bdevt_str(dev_t devt, char *buf)
@@ -499,8 +469,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 			      const struct attribute_group **groups,
 			      bool register_queue)
 {
-	dev_t devt;
-	int retval;
+	int ret;
 
 	/*
 	 * The disk queue should now be all set with enough information about
@@ -511,24 +480,30 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 	if (register_queue)
 		elevator_init_mq(disk->queue);
 
-	/* minors == 0 indicates to use ext devt from part0 and should
-	 * be accompanied with EXT_DEVT flag.  Make sure all
-	 * parameters make sense.
+	/*
+	 * If the driver provides an explicit major number it also must provide
+	 * the number of minors numbers supported, and those will be used to
+	 * setup the gendisk.
+	 * Otherwise just allocate the device numbers for both the whole device
+	 * and all partitions from the extended dev_t space.
 	 */
-	WARN_ON(disk->minors && !(disk->major || disk->first_minor));
-	WARN_ON(!disk->minors &&
-		!(disk->flags & (GENHD_FL_EXT_DEVT | GENHD_FL_HIDDEN)));
+	if (disk->major) {
+		WARN_ON(!disk->minors);
+	} else {
+		WARN_ON(disk->minors);
+		WARN_ON(!(disk->flags & (GENHD_FL_EXT_DEVT | GENHD_FL_HIDDEN)));
+
+		ret = blk_alloc_ext_minor();
+		if (ret < 0) {
+			WARN_ON(1);
+			return;
+		}
+		disk->major = BLOCK_EXT_MAJOR;
+		disk->first_minor = MINOR(ret);
+	}
 
 	disk->flags |= GENHD_FL_UP;
 
-	retval = blk_alloc_devt(disk->part0, &devt);
-	if (retval) {
-		WARN_ON(1);
-		return;
-	}
-	disk->major = MAJOR(devt);
-	disk->first_minor = MINOR(devt);
-
 	disk_alloc_events(disk);
 
 	if (disk->flags & GENHD_FL_HIDDEN) {
@@ -541,14 +516,14 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 	} else {
 		struct backing_dev_info *bdi = disk->queue->backing_dev_info;
 		struct device *dev = disk_to_dev(disk);
-		int ret;
 
 		/* Register BDI before referencing it from bdev */
-		dev->devt = devt;
-		ret = bdi_register(bdi, "%u:%u", MAJOR(devt), MINOR(devt));
+		dev->devt = MKDEV(disk->major, disk->first_minor);
+		ret = bdi_register(bdi, "%u:%u",
+				   disk->major, disk->first_minor);
 		WARN_ON(ret);
 		bdi_set_owner(bdi, dev);
-		bdev_add(disk->part0, devt);
+		bdev_add(disk->part0, dev->devt);
 	}
 	register_disk(parent, disk, groups);
 	if (register_queue)
@@ -1120,7 +1095,8 @@ static void disk_release(struct device *dev)
 
 	might_sleep();
 
-	blk_free_devt(dev->devt);
+	if (MAJOR(dev->devt) == BLOCK_EXT_MAJOR)
+		blk_free_ext_minor(MINOR(dev->devt));
 	disk_release_events(disk);
 	kfree(disk->random);
 	xa_destroy(&disk->part_tbl);

block/partitions/core.c

@@ -260,7 +260,8 @@ static const struct attribute_group *part_attr_groups[] = {
 
 static void part_release(struct device *dev)
 {
-	blk_free_devt(dev->devt);
+	if (MAJOR(dev->devt) == BLOCK_EXT_MAJOR)
+		blk_free_ext_minor(MINOR(dev->devt));
 	bdput(dev_to_bdev(dev));
 }
 
@@ -379,9 +380,15 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 	pdev->type = &part_type;
 	pdev->parent = ddev;
 
-	err = blk_alloc_devt(bdev, &devt);
-	if (err)
-		goto out_put;
+	/* in consecutive minor range? */
+	if (bdev->bd_partno < disk->minors) {
+		devt = MKDEV(disk->major, disk->first_minor + bdev->bd_partno);
+	} else {
+		err = blk_alloc_ext_minor();
+		if (err < 0)
+			goto out_put;
+		devt = MKDEV(BLOCK_EXT_MAJOR, err);
+	}
 	pdev->devt = devt;
 
 	/* delay uevent until 'holders' subdir is created */