Re: Any bio_clone_slow() implementation which doesn't share bi_io_vec?

[Christoph Hellwig <hch@infradead.org>]

On Tue, Nov 23, 2021 at 02:44:32PM +0800, Qu Wenruo wrote:
> Hi,
> 
> Although there are some out-of-date comments mentions other
> bio_clone_*() variants, but there isn't really any other bio clone
> variants other than __bio_clone_fast(), which shares bi_io_vec with the
> source bio.
> 
> This limits means we can't free the source bio before the cloned one.
> 
> Is there any bio_clone variant which do a deep clone, including bi_io_vec?

There is no use case for that, unless the actual data changes like in
the bounce buffering code.

> That's why the bio_clone thing is involved, there is still some corner
> cases that we don't want to fail the whole large bio if there is only
> one stripe failed (mostly for read bio, that we want to salvage as much
> data as possible)
> 
> Thus regular bio_split() + bio_chain() solution is not that good here.
> 
> Any idea why no such bio_clone_slow() or bio_split_slow() provided in
> block layer?
> 
> Or really bio_split() + bio_chain() is the only recommended solution?

You can use bio_split witout bio_chain.  You just need your own
bi_end_io handler that first performs the action you want and then
contains code equivalent to __bio_chain_endio.  As a bonus you can
pint bi_private to whatever you want, it does not have to be the parent
bio, just something that allows you to find it.