Draft: io_uring: introduce a generic samba_io_uring layer and convert vfs_io_uring to use it

Stefan Metzmacherrequested to merge
samba-team/devel/samba:metze-vfs-io-uring into master

This makes the code independent of the system liburing and adds some infrastructure to detect the available kernel features instead.

It means when the kernel provides io_uring, each tevent_context from samba_tevent_context_init() will be able to provide io_uring calls in a generic way.

We convert vfs_io_uring to use this generic layer and add 'io_uring:force_async_{read,write}_threshold' options in order to force IOSQE_ASYNC in order to offload memcpy to helper threads.

In future we'll use it for the smb client and server to offload sendmsg/recvmsg to IORING_OP_SENDMSG/RECVMSG with IOSQE_ASYNC to move memcpy to a helper thread.

Checklist

  • Commits have Signed-off-by: with name/author being identical to the commit author
  • (optional) This MR is just one part towards a larger feature.
  • (optional, if backport required) Bugzilla bug filed and BUG: tag added
  • Test suite updated with functionality tests
  • Test suite updated with negative tests
  • Documentation updated
  • CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

  • There is a test suite reasonably covering new functionality or modifications
  • Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
  • This feature/change has adequate documentation added
  • No obvious mistakes in the code

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