[Bug 1884719] Re: Function not implemented when using libaio

[Laurent Vivier]

Martin,

after a first look, I can see that asynchronicity introduces more
complexity in QEMU than usual ...

I'm going to try to write the patches. I will ask you some help to test
them.

I've already implemented io_setup and io_destroy, but io_submit
introduces more complexity because we can only cleanup qemu internal
buffers when the I/O are done. To do that we need to intercept events at
io_getevents level.


I will push my patches here:

https://github.com/vivier/qemu/commits/linux-user-libaio

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https://bugs.launchpad.net/bugs/1884719

Title:
  Function not implemented when using libaio

Status in QEMU:
  New

Bug description:
  Hello

  I experience "Function not implemented" errors when trying to use
  Linux libaio library in foreign architecture, e.g. aarch64.

  I've faced this problem while using 
https://github.com/multiarch/qemu-user-static, i.e. Docker+QEMU. 
  I understand that I do not use plain QEMU and you may count this report as a 
"distribution of QEMU"! Just let me know what are the steps to test it with 
plain QEMU and I will test and update this ticket!

  
  Here are the steps to reproduce the issue:

  1) On x86_64 machine register QEMU:

      `docker run -it --rm --privileged multiarch/qemu-user-static
  --reset --credential yes --persistent yes`

  2) Start a Docker image with foreign CPU architecture, e.g. aarch64

      `docker run -it arm64v8/centos:8 bash`

  3) Inside the Docker container install GCC and libaio

      `yum install gcc libaio libaio-devel`

  4) Compile the following C program

  ```
  #include <stdio.h>
  #include <errno.h>
  #include <libaio.h>
  #include <stdlib.h>

  struct io_control {
      io_context_t ioContext;
  };

  int main() {
      int queueSize = 10;

      struct io_control * theControl = (struct io_control *) 
malloc(sizeof(struct io_control));
      if (theControl == NULL) {
          printf("theControl is NULL");
          return 123;
      }

      int res = io_queue_init(queueSize, &theControl->ioContext);
      io_queue_release(theControl->ioContext);
      free(theControl);
      printf("res is: %d", res);
  }
  ```

      ```
      cat > test.c
          [PASTE THE CODE ABOVE HERE]
      ^D
      ```

      `gcc test.c -o out -laio && ./out`

  
  When executed directly on aarch64 machine (i.e. without emulation) or on 
x86_64 Docker image (e.g. centos:8) it prints `res is: 0`, i.e. it successfully 
initialized a LibAIO queue.

  But when executed on Docker image with foreign/emulated CPU
  architecture it prints `res is: -38` (ENOSYS). `man io_queue_init`
  says that error ENOSYS is returned when "Not implemented."

  Environment:

  QEMU version: 5.0.0.2  
(https://github.com/multiarch/qemu-user-static/blob/master/.travis.yml#L24-L28)
  Container application: Docker
  Output of `docker --version`:

  ```
  Client:
   Version:           19.03.8
   API version:       1.40
   Go version:        go1.13.8
   Git commit:        afacb8b7f0
   Built:             Wed Mar 11 23:42:35 2020
   OS/Arch:           linux/amd64
   Experimental:      false

  Server:
   Engine:
    Version:          19.03.8
    API version:      1.40 (minimum version 1.12)
    Go version:       go1.13.8
    Git commit:       afacb8b7f0
    Built:            Wed Mar 11 22:48:33 2020
    OS/Arch:          linux/amd64
    Experimental:     false
   containerd:
    Version:          1.3.3-0ubuntu2
    GitCommit:        
   runc:
    Version:          spec: 1.0.1-dev
    GitCommit:        
   docker-init:
    Version:          0.18.0
    GitCommit:        
  ```

  Same happens with Ubuntu (arm64v8/ubuntu:focal).

  I've tried to `strace` it but :

  ```
  /usr/bin/strace: ptrace(PTRACE_TRACEME, ...): Function not implemented
  /usr/bin/strace: PTRACE_SETOPTIONS: Function not implemented
  /usr/bin/strace: detach: waitpid(112): No child processes
  /usr/bin/strace: Process 112 detached
  ```

  Here are the steps to reproduce the problem with strace:

       ```
       docker run --rm -it --security-opt seccomp:unconfined --security-opt 
apparmor:unconfined --privileged --cap-add ALL arm64v8/centos:8 bash

       yum install -y strace`

       strace echo Test
       ```

  Note: I used --privileged, disabled seccomp and apparmor, and added
  all capabilities

  Disabling security solves the "Permission denied" problem but then
  comes the "Not implemented" one.

  
  Any idea what could be the problem and how to work it around ?
  I've googled a lot but I wasn't able to find any problems related to libaio 
on QEMU.

  Thank you!
  Martin

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