Re: [PATCH] the dm-loop target

[Matthew Wilcox <willy@infradead.org>]

On Mon, Mar 03, 2025 at 07:13:49AM -0800, Christoph Hellwig wrote:
> No, ->bmap is fundamentally flawed.  No new code should be using it, and
> we need to move the places still using it (most notably swap and the md
> bitmap code) off it.  It can't deal with any kind of changes to the file
> system topology and is a risk to data corruption because if used in the
> I/O path it bypasses the file system entirely..  If it wasn't we'd use it
> in the loop driver.

Funnily, I was looking at the md bitmap code too.  It's the last part of
the kernel using buffer heads with not-a-pagecache page, so it's the
only caller of alloc_page_buffers() remaining.

I think it should just use the page cache to read/write the file data,
but I haven't looked into it in detail.