Re: [PATCH v2] Do a proper locking for mmap and block size change

Christoph Hellwig
2012-11-30T16:36:37Z

On Fri, Nov 30, 2012 at 01:49:10PM +1100, Dave Chinner wrote:
> > Ugh. That's a big violation of how buffer-heads are supposed to work:
> > the block number is very much defined to be in multiples of b_size
> > (see for example "submit_bh()" that turns it into a sector number).
> >
> > But you're right. The direct-IO code really *is* violating that, and
> > knows that get_block() ends up being defined in i_blkbits regardless
> > of b_size.
>
> Same with mpage_readpages(), so it's not just direct IO that has
> this problem....

The mpage code may actually fall back to BHs.

I have a version of the direct I/O code that uses the iomap_ops from the
multi-page write code that you originally started. It uses the new op
as primary interface for direct I/O and provides a helper for
filesystems that still use buffer heads internally. I'll try to dust it
off and send out a version for the current kernel.