Chaining accept+read

[Ben Noordhuis <info@bnoordhuis.nl>]

I'm trying to chain accept+read but it's not working.

My code looks like this:

    *sqe1 = (struct io_uring_sqe){
      .opcode     = IORING_OP_ACCEPT,
      .flags      = IOSQE_IO_LINK,
      .fd         = listenfd,
      .file_index = 42, // or 42+1
    };
    *sqe2 = (struct io_uring_sqe){
      .opcode     = IORING_OP_READ,
      .flags      = IOSQE_FIXED_FILE,
      .addr       = (u64) buf,
      .len        = len,
      .fd         = 42,
    };
    submit();

Both ops fail immediately; accept with -ECANCELED, read with -EBADF,
presumably because fixed fd 42 doesn't exist at the time of submission.

Would it be possible to support this pattern in io_uring or are there
reasons for why things are the way they are?