Re: [PATCH 2/4] pass b_size to ->get_block()

[Andrew Morton <akpm@osdl.org>]

Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
> Pass amount of disk needs to be mapped to get_block().
> This way one can modify the fs ->get_block() functions 
> to map multiple blocks at the same time.

I can't say I terribly like this patch.  Initialising b_size all over the
place seems fragile.

We're _already_ setting bh.b_size to the right thing in
alloc_page_buffers(), and for a bh which is attached to
pagecache_page->private, there's no reason why b_size would ever change.

So what I think I'll do is to convert those places where you're needlessly
assigning to b_size into temporary WARN_ON(b_size != blocksize).

The only place where we need to initialise b_size is where we've got a
non-pagecache bh allocated on the stack.

We need to be sure that no ->get_block() implementations write garbage into
bh->b_size if something goes wrong.  b_size on a pagecache-based
buffer_head must remain inviolate.