Re: [RFC PATCH 02/17] block: simplify bio_add_page()

Christoph Hellwig
2014-12-23T10:22:23Z

On Mon, Dec 22, 2014 at 12:48:29PM +0100, Dongsu Park wrote:
> From: Kent Overstreet <kmo@daterainc.com>
>
> Since generic_make_request() can now handle arbitrary size bios, all we
> have to do is make sure the bvec array doesn't overflow.
> __bio_add_page() doesn't need to call ->merge_bvec_fn(), where
> we can get rid of unnecessary code paths.

This needs an explanation of why removign the call to ->merge_bvec_fn
is fine for bio_add_pc_page. I guess it's because neither
the target pscsi pass through mode, nor the osd code ever use anything
but a simple scsi devices that doesn't even have one, but it needs to be
clearly spelled out.

> + * Attempt to add a page to the bio_vec maplist. This will only fail if
> + * bio->bi_vcnt == bio->bi_max_vecs.

It also fails on a cloned bio, although that might better be turned into
a BUG_ON().