On Thu, May 05, 2016 at 11:54:22AM -0400, Mike Snitzer wrote:
> Commit 326e1dbb57 ("block: remove management of bi_remaining when
> restoring original bi_end_io") made bio_inc_remaining() private to bio.c
> because the only use-case that made sense was confined to the
> bio_chain() interface.
>
> Since that time DM thinp went on to use bio_chain() in its relatively
> complex implementation of async discard support. That implementation,
> even when converted over to use the new async __blkdev_issue_discard()
> interface, depends on deferred completion of the original discard bio --
> which is most appropriately implemented using bio_inc_remaining().
Can you explain that code flow to me? I still fail to why exactly
dm-thinp (and only dm-thinp) needs this. Maybe start by pointing me
to the additional bio_endio that pairs with the bio_inc_remaining
call.
> All said, bio_inc_remaining() should really only be used in conjunction
> with bio_chain(). It isn't intended for generic bio reference counting.
It's obviously used outside bio_chain in dm-thinp, so this sentence
doesn't make too much sense to me.
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