From: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
To: Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: Dave Kleikamp <shaggy-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
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"Darrick J. Wong"
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Joseph Qi
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re
Subject: Re: [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle
Date: Fri, 25 Aug 2023 15:47:56 +0200 [thread overview]
Message-ID: <20230825134756.o3wpq6bogndukn53@quack3> (raw)
In-Reply-To: <20230825015843.GB95084@ZenIV>
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-IBi9RG/b67k@public.gmane.org>
SUSE Labs, CR
next prev parent reply other threads:[~2023-08-25 13:47 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-11 11:04 [PATCH v2 0/29] block: Make blkdev_get_by_*() return handle Jan Kara
2023-08-11 12:27 ` Christoph Hellwig
2023-08-25 1:58 ` Al Viro
2023-08-25 13:47 ` Jan Kara [this message]
2023-08-26 2:28 ` Al Viro
2023-08-28 14:27 ` Christoph Hellwig
2023-08-28 13:20 ` Christian Brauner
2023-08-28 14:22 ` Christoph Hellwig
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