Re: [PATCH 6/6] fs: Make bind mounts work with bdev_allow_write_mounted=n

Christian Brauner
2023-07-07T07:39:15Z

On Thu, Jul 06, 2023 at 06:12:55PM +0200, Jan Kara wrote:
> On Thu 06-07-23 08:55:18, Christoph Hellwig wrote:
> > On Tue, Jul 04, 2023 at 02:56:54PM +0200, Jan Kara wrote:
> > > When we don't allow opening of mounted block devices for writing, bind
> > > mounting is broken because the bind mount tries to open the block device
> > > before finding the superblock for it already exists. Reorganize the
> > > mounting code to first look whether the superblock for a particular
> > > device is already mounted and open the block device only if it is not.
> >
> > Warning: this might be a rathole.
> >
> > I really hate how mount_bdev / get_tree_bdev try to deal with multiple
> > mounts.
> >
> > The idea to just open the device and work from there just feels very
> > bogus.
> >
> > There is really no good reason to have the bdev to find a superblock,
> > the dev_t does just fine (and in fact I have a patch to remove
> > the bdev based get_super and just use the dev_t based one all the
> > time). So I'd really like to actually turn this around and only
> > open when we need to allocate a new super block. That probably
> > means tearning sget_fc apart a bit, so it will turn into a fair
> > amount of work, but I think it's the right thing to do.
>
> Well, this is exactly what this patch does - we use dev_t to lookup the
> superblock in sget_fc() and we open the block device only if we cannot find
> matching superblock and need to create a new one...

Can you do this rework independent of the bdev_handle work that you're
doing so this series doesn't depend on the other work and we can get
the VFS bits merged for this?