On Wed, Dec 09 2020 at  8:01am -0500,
Sergei Shtepa [off-list ref] wrote:

Hi all.

I try to suggest the Block Layer Interposer (blk_interposer) again.
It`s allows to intercept bio requests, remap bio to another devices
or add new bios.

Initially, blk_interposer was designed to be compatible with
device mapper. Our (my and Hannes) previous attempt to offer
blk_interposer integrated with device mapper did not receive
any comments from the dm-devel team, and without their help
I will not be able to make a full implementation. I hope later
they will have time to support blk_interposer in device mapper.

Excuse me?  I gave you quite a bit of early feedback!  I then went on
PTO for ~10 days, when I returned last week I had to deal with fixing
some 5.10 dm/block bio splitting regressions that only got resolved this
past Saturday in time for 5.10-rc7.

blk_interposer was/is on my short list to review closer (Hannes' version
that refined yours a bit more).. primarily to see if I could avoid the
extra clone and endio hooking.

The development window for 5.11 is past, so you pushing this without
using the approach discussed (in terms of DM) doesn't help your cause.

And my blk-snap module requires an architecture change to
support blk_interposer.

This time I offer it along with a sample.
Despite the fact that blk_interposer is quite simple,
there are a few non-obvious points that I would like to clarify.

However, I suggest the blk_interposer now so that people
could discuss it and use it in their projects as soon as possible.

So you weren't willing to put the work in on something DM oriented
because you expected me to do the work for you?  And now you're looking
to side-step the consensus that was built because I didn't contribute
quick enough?  That's pretty messed up.

In the time-scale that is Linux kernel development.. you've really
jumped the gun and undercut my enthusiasm to work through the details.
I'd rather not read into your actions more than I already have here, but
I'm not liking what you've done here.  Kind of left in dismay with how
you decided to go down this path without a followup note to me or others
(that I'm aware of).

But I'm still willing to make blk_interposer work as we all discussed
(in terms of DM).

Mike

Sergei Shtepa (3):
  block: blk_interposer - Block Layer Interposer
  block: blk_interposer - sample
  block: blk_interposer - sample config

 block/blk-core.c                        |  32 +++
 include/linux/blk_types.h               |   6 +-
 include/linux/genhd.h                   |  12 +-
 samples/Kconfig                         |   7 +
 samples/Makefile                        |   1 +
 samples/blk_interposer/Makefile         |   2 +
 samples/blk_interposer/blk-interposer.c | 276 ++++++++++++++++++++++++
 7 files changed, 333 insertions(+), 3 deletions(-)
 create mode 100644 samples/blk_interposer/Makefile
 create mode 100644 samples/blk_interposer/blk-interposer.c

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2.20.1