block_device: add a pointer to struct address_space (page cache of bdev)

points to ->i_data of coallocated inode.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/20240411145346.2516848-1-viro@zeniv.linux.org.uk
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Al Viro

block/bdev.c

@@ -419,6 +419,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	mutex_init(&bdev->bd_holder_lock);
 	bdev->bd_partno = partno;
 	bdev->bd_inode = inode;
+	bdev->bd_mapping = &inode->i_data;
 	bdev->bd_queue = disk->queue;
 	if (partno)
 		bdev->bd_has_submit_bio = disk->part0->bd_has_submit_bio;

include/linux/blk_types.h

@@ -51,6 +51,7 @@ struct block_device {
 	bool			bd_has_submit_bio;
 	dev_t			bd_dev;
 	struct inode		*bd_inode;	/* will die */
+	struct address_space	*bd_mapping;	/* page cache */
 
 	atomic_t		bd_openers;
 	spinlock_t		bd_size_lock; /* for bd_inode->i_size updates */