Re: [RFC 4/4] bdev: extend bdev inode with it's own super_block

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jun 08, 2023 at 10:45:10AM -0700, Luis Chamberlain wrote:
> > > and then considering only two superblocks instead of having a list of
> > > all bdevs?
> > 
> > Or why the heck we would even do this to start with?
> 
> That's what I gathered you suggested at LSFMM on hallway talk.

No.  I explained you that sharing the superblock or has absolutely no
effct on the aops after you wanted to it.  I said it might be nice for
other reasons to have a sb per gendisk.

> > iomap has absolutely nothing to do with superblocks.
> > 
> > Now maybe it might make sense to have a superblock per gendisk just
> > to remove all the weird special casing for the bdev inode in the
> > writeback code.  But that's something entirely different than this
> > patch.
> 
> The goal behind this is to allow block devices to have its bdev cache
> use iomap, right now now we show-horn in the buffer-head aops if we
> have to build buffer-heads.
> 
> If this sort of approach is not desirable, let me know what alternative
> you would prefer to see, because clearly, I must not have understood
> your suggestion.

Again, every non-trivial file system right now has more than one set
of aops per superblock.  I'm not sure what problem you are trying to
solve here.