linux-kernel - [PATCH 11/19] loop: use __register_blkdev to allocate devices on demand

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Date:   Sun, 30 Aug 2020 08:24:37 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Denis Efremov <efremov@...ux.com>,
        "David S. Miller" <davem@...emloft.net>,
        Song Liu <song@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ide@...r.kernel.org, linux-raid@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-m68k@...ts.linux-m68k.org
Subject: [PATCH 11/19] loop: use __register_blkdev to allocate devices on demand

Use the simpler mechanism attached to major_name to allocate a brd device
when a currently unregistered minor is accessed.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 drivers/block/loop.c | 30 ++++++++----------------------
 1 file changed, 8 insertions(+), 22 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 5a991510136225..7c944a425f718f 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2234,24 +2234,18 @@ static int loop_lookup(struct loop_device **l, int i)
 	return ret;
 }
 
-static struct kobject *loop_probe(dev_t dev, int *part, void *data)
+static void loop_probe(dev_t dev)
 {
+	int idx = MINOR(dev) >> part_shift;
 	struct loop_device *lo;
-	struct kobject *kobj;
-	int err;
+
+	if (max_loop && idx >= max_loop)
+		return;
 
 	mutex_lock(&loop_ctl_mutex);
-	err = loop_lookup(&lo, MINOR(dev) >> part_shift);
-	if (err < 0)
-		err = loop_add(&lo, MINOR(dev) >> part_shift);
-	if (err < 0)
-		kobj = NULL;
-	else
-		kobj = get_disk_and_module(lo->lo_disk);
+	if (loop_lookup(&lo, idx) < 0)
+		loop_add(&lo, idx);
 	mutex_unlock(&loop_ctl_mutex);
-
-	*part = 0;
-	return kobj;
 }
 
 static long loop_control_ioctl(struct file *file, unsigned int cmd,
@@ -2371,14 +2365,11 @@ static int __init loop_init(void)
 		goto err_out;
 
 
-	if (register_blkdev(LOOP_MAJOR, "loop")) {
+	if (__register_blkdev(LOOP_MAJOR, "loop", loop_probe)) {
 		err = -EIO;
 		goto misc_out;
 	}
 
-	blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
-				  THIS_MODULE, loop_probe, NULL, NULL);
-
 	/* pre-create number of devices given by config or max_loop */
 	mutex_lock(&loop_ctl_mutex);
 	for (i = 0; i < nr; i++)
@@ -2404,16 +2395,11 @@ static int loop_exit_cb(int id, void *ptr, void *data)
 
 static void __exit loop_exit(void)
 {
-	unsigned long range;
-
-	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
-
 	mutex_lock(&loop_ctl_mutex);
 
 	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
 	idr_destroy(&loop_index_idr);
 
-	blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
 	unregister_blkdev(LOOP_MAJOR, "loop");
 
 	misc_deregister(&loop_misc);
-- 
2.28.0