block: deprecate autoloading based on dev_t

Make the legacy dev_t based autoloading optional and add a deprecation
warning.  This kind of autoloading has ceased to be useful about 20 years
ago.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220104071647.164918-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/Kconfig

@@ -26,6 +26,18 @@ menuconfig BLOCK
 
 if BLOCK
 
+config BLOCK_LEGACY_AUTOLOAD
+	bool "Legacy autoloading support"
+	help
+	  Enable loading modules and creating block device instances based on
+	  accesses through their device special file.  This is a historic Linux
+	  feature and makes no sense in a udev world where device files are
+	  created on demand.
+
+	  Say N here unless booting or other functionality broke without it, in
+	  which case you should also send a report to your distribution and
+	  linux-block@vger.kernel.org.
+
 config BLK_RQ_ALLOC_TIME
 	bool
 

block/bdev.c

@@ -733,12 +733,15 @@ struct block_device *blkdev_get_no_open(dev_t dev)
 	struct inode *inode;
 
 	inode = ilookup(blockdev_superblock, dev);
-	if (!inode) {
+	if (!inode && IS_ENABLED(CONFIG_BLOCK_LEGACY_AUTOLOAD)) {
 		blk_request_module(dev);
 		inode = ilookup(blockdev_superblock, dev);
+		if (inode)
+			pr_warn_ratelimited(
+"block device autoloading is deprecated. It will be removed in Linux 5.19\n");
+	}
 	if (!inode)
 		return NULL;
-	}
 
 	/* switch from the inode reference to a device mode one: */
 	bdev = &BDEV_I(inode)->bdev;

block/genhd.c

@@ -185,7 +185,9 @@ static struct blk_major_name {
 	struct blk_major_name *next;
 	int major;
 	char name[16];
+#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
 	void (*probe)(dev_t devt);
+#endif
 } *major_names[BLKDEV_MAJOR_HASH_SIZE];
 static DEFINE_MUTEX(major_names_lock);
 static DEFINE_SPINLOCK(major_names_spinlock);
@@ -275,7 +277,9 @@ int __register_blkdev(unsigned int major, const char *name,
 	}
 
 	p->major = major;
+#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
 	p->probe = probe;
+#endif
 	strlcpy(p->name, name, sizeof(p->name));
 	p->next = NULL;
 	index = major_to_index(major);
@@ -679,6 +683,7 @@ static ssize_t disk_badblocks_store(struct device *dev,
 	return badblocks_store(disk->bb, page, len, 0);
 }
 
+#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
 void blk_request_module(dev_t devt)
 {
 	unsigned int major = MAJOR(devt);
@@ -698,6 +703,7 @@ void blk_request_module(dev_t devt)
 		/* Make old-style 2.4 aliases work */
 		request_module("block-major-%d", MAJOR(devt));
 }
+#endif /* CONFIG_BLOCK_LEGACY_AUTOLOAD */
 
 /*
  * print a full list of all partitions - intended for places where the root