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

Dongsu Park
2014-12-23T11:46:47Z

On 23.12.2014 02:22, Christoph Hellwig wrote:
> 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.

Agreed.

> > + * 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().

Agreed, I'll update both of them in the next round.

Thanks,
Dongsu