On Sat, Apr 06, 2024 at 08:42:06PM +0100, Al Viro wrote: > On Sat, Apr 06, 2024 at 05:09:26PM +0800, Yu Kuai wrote: > > From: Yu Kuai <yukuai3@xxxxxxxxxx> > > > > So that iomap and bffer_head can convert to use bdev_file in following > > patches. > > Let me see if I got it straight. You introduce dummy struct file instances > (no methods, nothing). The *ONLY* purpose they serve is to correspond to > opened instances of struct bdev. No other use is possible. > > You shove them into ->i_private of bdevfs inodes. Lifetime rules are... > odd. > > In bdev_open() you arrange for such beast to be present. You never > return it anywhere, they only get accessed via ->i_private, exposing > it at least to fs/buffer.c. Reference to those suckers get stored > (without grabbing refcount) into buffer_head instances. > > And all of that is for... what, exactly? Put another way, what's the endgame here? Are you going to try and propagate those beasts down into bio_alloc()? Because if you do not, you need to keep struct block_device * around anyway. We use ->b_bdev for several things: * passing to bio_alloc() (quite a few places) * %pg in debugging printks * (rare) passing to write_boundary_block(). * (twice) passing to clean_bdev_aliases(). * (once) passing to __find_get_block(). * one irregular use as a key in lookup_bh_lru() IDGI...
