On Fri 25-08-23 02:58:43, Al Viro wrote: > On Fri, Aug 11, 2023 at 01:04:31PM +0200, Jan Kara wrote: > > Hello, > > > > this is a v2 of the patch series which implements the idea of blkdev_get_by_*() > > calls returning bdev_handle which is then passed to blkdev_put() [1]. This > > makes the get and put calls for bdevs more obviously matching and allows us to > > propagate context from get to put without having to modify all the users > > (again!). In particular I need to propagate used open flags to blkdev_put() to > > be able count writeable opens and add support for blocking writes to mounted > > block devices. I'll send that series separately. > > > > The series is based on Christian's vfs tree as of yesterday as there is quite > > some overlap. Patches have passed some reasonable testing - I've tested block > > changes, md, dm, bcache, xfs, btrfs, ext4, swap. This obviously doesn't cover > > everything so I'd like to ask respective maintainers to review / test their > > changes. Thanks! I've pushed out the full branch to: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git bdev_handle > > > > to ease review / testing. > > Hmm... Completely Insane Idea(tm): how about turning that thing inside out and > having your bdev_open_by... return an actual opened struct file? > > After all, we do that for sockets and pipes just fine and that's a whole lot > hotter area. > > Suppose we leave blkdev_open()/blkdev_release() as-is. No need to mess with > what we have for normal opened files for block devices. And have block_open_by_dev() > that would find bdev, etc., same yours does and shove it into anon file. > > Paired with plain fput() - no need to bother with new primitives for closing. > With a helper returning I_BDEV(bdev_file_inode(file)) to get from those to bdev. > > NOTE: I'm not suggesting replacing ->s_bdev with struct file * if we do that - > we want that value cached, obviously. Just store both... > > Not saying it's a good idea, but... might be interesting to look into. > Comments? I can see the appeal of not having to introduce the new bdev_handle type and just using struct file which unifies in-kernel and userspace block device opens. But I can see downsides too - the last fput() happening from task work makes me a bit nervous whether it will not break something somewhere with exclusive bdev opens. Getting from struct file to bdev is somewhat harder but I guess a helper like F_BDEV() would solve that just fine. So besides my last fput() worry about I think this could work and would be probably a bit nicer than what I have. But before going and redoing the whole series let me gather some more feedback so that we don't go back and forth. Christoph, Christian, Jens, any opinion? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
