[PATCH v5 00/12] blkio: add libblkio BlockDriver

[Stefan Hajnoczi <stefanha@redhat.com>]

v5:
- Drop "RFC" since libblkio 1.0 has been released and the library API is stable
- Disable BDRV_REQ_REGISTERED_BUF if we run out of blkio_mem_regions. The
  bounce buffer slow path is taken when there are not enough blkio_mem_regions
  to cover guest RAM. [Hanna & David Hildenbrand]
- Call ram_block_discard_disable() when mem-region-pinned property is true or
  absent [David Hildenbrand]
- Use a bounce buffer pool instead of allocating/freeing a buffer for each
  request. This reduces the number of blkio_mem_regions required for bounce
  buffers to 1 and avoids frequent blkio_mem_region_map/unmap() calls.
- Switch to .bdrv_co_*() instead of .bdrv_aio_*(). Needed for the bounce buffer
  pool's CoQueue.
v4:
- Patch 1:
  - Add virtio-blk-vhost-user driver [Kevin]
  - Drop .bdrv_parse_filename() and .bdrv_needs_filename for virtio-blk-vhost-vdpa [Stefano]
  - Add copyright and license header [Hanna]
  - Drop .bdrv_parse_filename() in favor of --blockdev or json: [Hanna]
  - Clarify that "filename" is always non-NULL for io_uring [Hanna]
  - Check that virtio-blk-vhost-vdpa "path" option is non-NULL [Hanna]
  - Fix virtio-blk-vhost-vdpa cache.direct=off logic [Hanna]
  - Use macros for driver names [Hanna]
  - Assert that the driver name is valid [Hanna]
  - Update "readonly" property name to "read-only" [Hanna]
  - Call blkio_detach_aio_context() in blkio_close() [Hanna]
  - Avoid uint32_t * to int * casts in blkio_refresh_limits() [Hanna]
  - Remove write zeroes and discard from the todo list [Hanna]
  - Use PRIu32 instead of %d for uint32_t [Hanna]
  - Fix error messages with buf-alignment instead of optimal-io-size [Hanna]
  - Call map/unmap APIs since libblkio alloc/free APIs no longer do that
  - Update QAPI schema QEMU version to 7.2
- Patch 5:
  - Expand the BDRV_REQ_REGISTERED_BUF flag passthrough and drop assert(!flags)
    in drivers [Hanna]
- Patch 7:
  - Fix BLK->BDRV typo [Hanna]
  - Make BlockRAMRegistrar handle failure [Hanna]
- Patch 8:
  - Replace memory_region_get_fd() approach with qemu_ram_get_fd()
- Patch 10:
  - Use (void)ret; to discard unused return value [Hanna]
  - libblkio's blkio_unmap_mem_region() API no longer has a return value
  - Check for registered bufs that cross RAMBlocks [Hanna]
- Patch 11:
  - Handle bdrv_register_buf() errors [Hanna]
v3:
- Add virtio-blk-vhost-vdpa for vdpa-blk devices including VDUSE
- Add discard and write zeroes support
- Rebase and adopt latest libblkio APIs
v2:
- Add BDRV_REQ_REGISTERED_BUF to bs.supported_write_flags [Stefano]
- Use new blkioq_get_num_completions() API
- Implement .bdrv_refresh_limits()

This patch series adds a QEMU BlockDriver for libblkio
(https://gitlab.com/libblkio/libblkio/), a library for high-performance block
device I/O. This work was presented at KVM Forum 2022 and slides are available
here:
https://static.sched.com/hosted_files/kvmforum2022/8c/libblkio-kvm-forum-2022.pdf

The second patch adds the core BlockDriver and most of the libblkio API usage.
Three libblkio drivers are included:
- io_uring
- virtio-blk-vhost-user
- virtio-blk-vhost-vdpa

The remainder of the patch series reworks the existing QEMU bdrv_register_buf()
API so virtio-blk emulation efficiently map guest RAM for libblkio - some
libblkio drivers require that I/O buffer memory is pre-registered (think VFIO,
vhost, etc).

Vladimir requested performance results that show the effect of the
BDRV_REQ_REGISTERED_BUF flag. I ran the patches against qemu-storage-daemon's
vhost-user-blk export with iodepth=1 bs=512 to see the per-request overhead due
to bounce buffer allocation/mapping:

Name                                   IOPS   Error
bounce-buf                          4373.81 ± 0.01%
registered-buf                     13062.80 ± 0.67%

The BDRV_REQ_REGISTERED_BUF optimization version is about 3x faster.

See the BlockDriver struct in block/blkio.c for a list of APIs that still need
to be implemented. The core functionality is covered.

Regarding the design: each libblkio driver is a separately named BlockDriver.
That means there is an "io_uring" BlockDriver and not a generic "libblkio"
BlockDriver. This way QAPI and open parameters are type-safe and mandatory
parameters can be checked by QEMU.

Stefan Hajnoczi (12):
  coroutine: add flag to re-queue at front of CoQueue
  blkio: add libblkio block driver
  numa: call ->ram_block_removed() in ram_block_notifer_remove()
  block: pass size to bdrv_unregister_buf()
  block: use BdrvRequestFlags type for supported flag fields
  block: add BDRV_REQ_REGISTERED_BUF request flag
  block: return errors from bdrv_register_buf()
  block: add BlockRAMRegistrar
  exec/cpu-common: add qemu_ram_get_fd()
  stubs: add qemu_ram_block_from_host() and qemu_ram_get_fd()
  blkio: implement BDRV_REQ_REGISTERED_BUF optimization
  virtio-blk: use BDRV_REQ_REGISTERED_BUF optimization hint

 MAINTAINERS                                 |    7 +
 meson_options.txt                           |    2 +
 qapi/block-core.json                        |   53 +-
 meson.build                                 |    9 +
 include/block/block-common.h                |    9 +
 include/block/block-global-state.h          |   10 +-
 include/block/block_int-common.h            |   15 +-
 include/exec/cpu-common.h                   |    1 +
 include/hw/virtio/virtio-blk.h              |    2 +
 include/qemu/coroutine.h                    |   15 +-
 include/sysemu/block-backend-global-state.h |    4 +-
 include/sysemu/block-ram-registrar.h        |   37 +
 block.c                                     |   14 +
 block/blkio.c                               | 1017 +++++++++++++++++++
 block/blkverify.c                           |    4 +-
 block/block-backend.c                       |    8 +-
 block/block-ram-registrar.c                 |   54 +
 block/crypto.c                              |    4 +-
 block/file-posix.c                          |    1 -
 block/gluster.c                             |    1 -
 block/io.c                                  |  101 +-
 block/mirror.c                              |    2 +
 block/nbd.c                                 |    1 -
 block/nvme.c                                |   20 +-
 block/parallels.c                           |    1 -
 block/qcow.c                                |    2 -
 block/qed.c                                 |    1 -
 block/raw-format.c                          |    2 +
 block/replication.c                         |    1 -
 block/ssh.c                                 |    1 -
 block/vhdx.c                                |    1 -
 hw/block/virtio-blk.c                       |   39 +-
 hw/core/numa.c                              |   17 +
 qemu-img.c                                  |    6 +-
 softmmu/physmem.c                           |    5 +
 stubs/physmem.c                             |   13 +
 tests/qtest/modules-test.c                  |    3 +
 util/qemu-coroutine-lock.c                  |    9 +-
 util/vfio-helpers.c                         |    5 +-
 block/meson.build                           |    2 +
 scripts/meson-buildoptions.sh               |    3 +
 stubs/meson.build                           |    1 +
 42 files changed, 1412 insertions(+), 91 deletions(-)
 create mode 100644 include/sysemu/block-ram-registrar.h
 create mode 100644 block/blkio.c
 create mode 100644 block/block-ram-registrar.c
 create mode 100644 stubs/physmem.c

-- 
2.37.3