sg: do not allocate a gendisk

sg is a character driver and thus does not need to allocate a gendisk,
which is only used for file system-like block layer I/O on block
devices.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20210816131910.615153-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/sg.c

@@ -166,7 +166,7 @@ typedef struct sg_device { /* holds the state of each scsi generic device */
 	bool exclude;		/* 1->open(O_EXCL) succeeded and is active */
 	int open_cnt;		/* count of opens (perhaps < num(sfds) ) */
 	char sgdebug;		/* 0->off, 1->sense, 9->dump dev, 10-> all devs */
-	struct gendisk *disk;
+	char name[DISK_NAME_LEN];
 	struct cdev * cdev;	/* char_dev [sysfs: /sys/cdev/major/sg<n>] */
 	struct kref d_ref;
 } Sg_device;
@@ -202,8 +202,7 @@ static void sg_device_destroy(struct kref *kref);
 #define SZ_SG_REQ_INFO sizeof(sg_req_info_t)
 
 #define sg_printk(prefix, sdp, fmt, a...) \
-	sdev_prefix_printk(prefix, (sdp)->device,		\
-			   (sdp)->disk->disk_name, fmt, ##a)
+	sdev_prefix_printk(prefix, (sdp)->device, (sdp)->name, fmt, ##a)
 
 /*
  * The SCSI interfaces that use read() and write() as an asynchronous variant of
@@ -832,7 +831,7 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
 
 	srp->rq->timeout = timeout;
 	kref_get(&sfp->f_ref); /* sg_rq_end_io() does kref_put(). */
-	blk_execute_rq_nowait(sdp->disk, srp->rq, at_head, sg_rq_end_io);
+	blk_execute_rq_nowait(NULL, srp->rq, at_head, sg_rq_end_io);
 	return 0;
 }
 
@@ -1119,8 +1118,7 @@ sg_ioctl_common(struct file *filp, Sg_device *sdp, Sg_fd *sfp,
 		return put_user(max_sectors_bytes(sdp->device->request_queue),
 				ip);
 	case BLKTRACESETUP:
-		return blk_trace_setup(sdp->device->request_queue,
-				       sdp->disk->disk_name,
+		return blk_trace_setup(sdp->device->request_queue, NULL,
 				       MKDEV(SCSI_GENERIC_MAJOR, sdp->index),
 				       NULL, p);
 	case BLKTRACESTART:
@@ -1456,7 +1454,7 @@ static struct class *sg_sysfs_class;
 static int sg_sysfs_valid = 0;
 
 static Sg_device *
-sg_alloc(struct gendisk *disk, struct scsi_device *scsidp)
+sg_alloc(struct scsi_device *scsidp)
 {
 	struct request_queue *q = scsidp->request_queue;
 	Sg_device *sdp;
@@ -1492,9 +1490,7 @@ sg_alloc(struct gendisk *disk, struct scsi_device *scsidp)
 
 	SCSI_LOG_TIMEOUT(3, sdev_printk(KERN_INFO, scsidp,
 					"sg_alloc: dev=%d \n", k));
-	sprintf(disk->disk_name, "sg%d", k);
-	disk->first_minor = k;
-	sdp->disk = disk;
+	sprintf(sdp->name, "sg%d", k);
 	sdp->device = scsidp;
 	mutex_init(&sdp->open_rel_lock);
 	INIT_LIST_HEAD(&sdp->sfds);
@@ -1521,19 +1517,11 @@ static int
 sg_add_device(struct device *cl_dev, struct class_interface *cl_intf)
 {
 	struct scsi_device *scsidp = to_scsi_device(cl_dev->parent);
-	struct gendisk *disk;
 	Sg_device *sdp = NULL;
 	struct cdev * cdev = NULL;
 	int error;
 	unsigned long iflags;
 
-	disk = alloc_disk(1);
-	if (!disk) {
-		pr_warn("%s: alloc_disk failed\n", __func__);
-		return -ENOMEM;
-	}
-	disk->major = SCSI_GENERIC_MAJOR;
-
 	error = -ENOMEM;
 	cdev = cdev_alloc();
 	if (!cdev) {
@@ -1543,7 +1531,7 @@ sg_add_device(struct device *cl_dev, struct class_interface *cl_intf)
 	cdev->owner = THIS_MODULE;
 	cdev->ops = &sg_fops;
 
-	sdp = sg_alloc(disk, scsidp);
+	sdp = sg_alloc(scsidp);
 	if (IS_ERR(sdp)) {
 		pr_warn("%s: sg_alloc failed\n", __func__);
 		error = PTR_ERR(sdp);
@@ -1561,7 +1549,7 @@ sg_add_device(struct device *cl_dev, struct class_interface *cl_intf)
 		sg_class_member = device_create(sg_sysfs_class, cl_dev->parent,
 						MKDEV(SCSI_GENERIC_MAJOR,
 						      sdp->index),
-						sdp, "%s", disk->disk_name);
+						sdp, "%s", sdp->name);
 		if (IS_ERR(sg_class_member)) {
 			pr_err("%s: device_create failed\n", __func__);
 			error = PTR_ERR(sg_class_member);
@@ -1589,7 +1577,6 @@ sg_add_device(struct device *cl_dev, struct class_interface *cl_intf)
 	kfree(sdp);
 
 out:
-	put_disk(disk);
 	if (cdev)
 		cdev_del(cdev);
 	return error;
@@ -1613,7 +1600,6 @@ sg_device_destroy(struct kref *kref)
 	SCSI_LOG_TIMEOUT(3,
 		sg_printk(KERN_INFO, sdp, "sg_device_destroy\n"));
 
-	put_disk(sdp->disk);
 	kfree(sdp);
 }
 
@@ -2606,7 +2592,7 @@ static int sg_proc_seq_show_debug(struct seq_file *s, void *v)
 		goto skip;
 	read_lock(&sdp->sfd_lock);
 	if (!list_empty(&sdp->sfds)) {
-		seq_printf(s, " >>> device=%s ", sdp->disk->disk_name);
+		seq_printf(s, " >>> device=%s ", sdp->name);
 		if (atomic_read(&sdp->detaching))
 			seq_puts(s, "detaching pending close ");
 		else if (sdp->device) {