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io_uring: CMD_FUSE_KBUF - Coggle Diagram

- - - - the 1st command is for seting up kernel bvec based buffer
      - the 2nd SQE consumes the kernel buffer
    - - it is actually one OP from user viewpoint
  - - - generic plugin callback
        
        ->provide_resource()
        
        ->consume_resource()
- - - - the 1st command should be done in sync submission in current context
    - - define ->prep_fuse_kbuf() cb for supported slave OPs
      - the callback is called inside fuse_kbuf_cmd->issue()
    - - if the 1st req is failed, the 2nd one won't be started
        
        io_uring already handle in this way
        
        req_set_fail
  - - - the 2nd req won't be issued if the 1st one is failed, so no cqe for 2nd req if the 1st cmd is failed
    - - then driver can complete this request
        
        need to export API for driver
      - just like send_zc's buffer notificaiton
  - - - link them together
        
        io_uring command is always prepared/issued before preparing/issuing the 2nd req
      - the 2nd req is populated with command's sqe payload
    - - 1st req is failed
      - the 2nd req is failed