[LINUX] Programs that use io_uring do not work with Docker on CentOS 8

There is an asynchronous IO kernel function called io_uring introduced from Linux kernel 5.1, but the Docker image that uses it does not work on CentOS 8. Well, for those who know it, that's right.

As a rationale if you want to argue that the portability of Docker/Linux containers isn't all-purpose.

io_uring Create a program to use on Ubuntu 20.10.

1. 1. Create a virtual machine with an OS of Ubuntu 20.10. https://ubuntu.com/download
2. 2. Install Docker. https://docs.docker.com/engine/install/ubuntu/
3. 3. Launch the Ubuntu 20.10 image on Docker.

20.10 bash

 4. For the time being, check the kernel in use with uname -a.
```(c)# uname -a```

(Execution result) root@17003dd74a2f:/liburing/examples# uname -a Linux 17003dd74a2f 5.8.0-33-generic #36-Ubuntu SMP Wed Dec 9 09:14:40 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

 5. Install gcc and io_uring libraries, git.
```(c)# apt-get update```
```(c)# apt-get install -y build-essential liburing-dev git```

 6. Get the sample program of io_uring.
https://blogs.oracle.com/linux/an-introduction-to-the-io_uring-asynchronous-io-framework

#### **`(c)# git clone https://github.com/axboe/liburing.git`**

7. Compile the sample program. (c)# cd liburing/examples

(c)# gcc -Wall -O2 -D_GNU_SOURCE -o io_uring-test io_uring-test.c -luring

 8. Run the program. Of course, this works.

#### **`(c)# ./io_uring-test io_uring-test.c`**

(Execution result)
root@08ad6f4c804c:/liburing/examples# ./io_uring-test io_uring-test.c
Submitted=1, completed=1, bytes=2256

9. Detach (C-p, C-q) from the container, commit, and save the image. # docker commit io_uring-test io_uring-test

# docker save io_uring-test -o io_uring-test.tar

# Run the program on CentOS 8 Docker

 1. 1. Create a virtual machine whose OS is CentOS 8.3.
https://www.centos.org/download/

 2. 2. Install Docker.
https://docs.docker.com/engine/install/centos/

 3. 3. Copy the previous Docker image (io_uring-test.tar) to your CentOS 8 machine and load it.

#### **`# docker load -i io_uring-test.tar`**
```tar


 4. Start the container.
```# docker run -it --rm io_uring-test bash```

 5. For the time being, check the kernel in use with uname -a. It should be 4.18, the same as the host CentOS 8.
```(c)# uname -a```

(Execution result) root@824c737193b6:/# uname -a Linux 824c737193b6 4.18.0-240.1.1.el8_3.x86_64 #1 SMP Thu Nov 19 17:20:08 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

(By the way) root@824c737193b6:/liburing/examples# cat /etc/os-release NAME="Ubuntu" VERSION="20.10 (Groovy Gorilla)" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 20.10" VERSION_ID="20.10" HOME_URL="https://www.ubuntu.com/" SUPPORT_URL="https://help.ubuntu.com/" BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/" PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy" VERSION_CODENAME=groovy UBUNTU_CODENAME=groovy

 5. Run the sample program.
```(c)# cd liburing/examples/```

#### **`(c)# ./io_uring-test io_uring-test.c`**

(Execution result)
root@824c737193b6:/liburing/examples# ./io_uring-test io_uring-test.c
queue_init: Function not implemented

Well, it doesn't work.