[RFC PATCH v2 0/7] Introduce a vringh accessor for IO memory

[Shunsuke Mie <mie@igel.co.jp>]

Vringh is a host-side implementation of virtio rings, and supports the
vring located on three kinds of memories, userspace, kernel space and a
space translated iotlb.

The goal of this patchset is to refactor vringh and introduce a new vringh
accessor for the vring located on the io memory region. The io memory
accessor (iomem) is used by a driver that is not published yet, but I'm
planning to publish it. Also changes of drivers affected by this patchset
are not included yet. e.g. caif_virtio and vdpa (sim_net,blk, net/mlx5)
drivers.

This patchset can separate into 4 parts:
1. Fix a typo in the vringh header[1/7]
2. Enable a retpoline on virtio/vringh_test [2/7]
2. Unify the vringh APIs and change related [3, 4, 5, 6/7]
3. Support IOMEM to vringh [7/7]

This first part is just for typo fixing. The second part changes build
options of virtio/vringh_test. The change bring the test close to linux
kernel in retpoline. In the third part, unify the vringh API for each
accessors that are user, kern and iotlb. The main point is struct
vringh_ops that fill the gap between all accessors. The final part
introduces an iomem support to vringh according to the unified API in the
second part.

Those changes are tested for the user accessor using vringh_test and kern
and iomem using a non published driver, but I think I can add a link to a
patchset for the driver in the next version of this patchset.

v2:
- Add a build options to enable the retpoline in vringh_test
- Add experimental results of the API unification

v1: https://lore.kernel.org/virtualization/20221227022528.609839-1-mie@igel.co.jp/
- Initial patchset

Shunsuke Mie (7):
  vringh: fix a typo in comments for vringh_kiov
  tools/virtio: enable to build with retpoline
  vringh: remove vringh_iov and unite to vringh_kiov
  tools/virtio: convert to new vringh user APIs
  vringh: unify the APIs for all accessors
  tools/virtio: convert to use new unified vringh APIs
  vringh: IOMEM support

 drivers/vhost/Kconfig      |   6 +
 drivers/vhost/vringh.c     | 721 ++++++++++++-------------------------
 include/linux/vringh.h     | 147 +++-----
 tools/virtio/Makefile      |   2 +-
 tools/virtio/vringh_test.c | 123 ++++---
 5 files changed, 357 insertions(+), 642 deletions(-)

-- 
2.25.1

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