No ulimit validation in the daemon.json

[fanjiyun]

Description
I found that there was no ulimit validation in the daemon.json, but the dockerd flag has. Why? Are there any special considerations?

Steps to reproduce the issue:

1. Set up the daemon.json as follows. ulimit soft limit is greater than hard limit.

$ cat /etc/docker/daemon.json
{
    "default-ulimits": {
         "core": {
             "Name": "core",
             "Soft": 2048,
             "Hard": 1024
        }
    }
}

2. Start the docker service. Service started successfully.

$ systemctl restart docker
$ systemctl status docker
● docker.service - Docker Application Container Engine
   Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
   Active: active (running) since Mon 2019-11-25 19:58:39 CST; 7s ago
     Docs: https://docs.docker.com
 Main PID: 30454 (dockerd)
    Tasks: 44
   Memory: 41.9M
   CGroup: /system.slice/docker.service
           └─30454 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

3. Stop the docker service. Then, start docked in the following ways, but docked fails to start.

$ dockerd --default-ulimit core=2048:1024
Status: invalid argument "core=2048:1024" for "--default-ulimit" flag: ulimit soft limit must be less than or equal to hard limit: 2048 > 1024
See 'dockerd --help'., Code: 125

1. Set up the daemon.json as follows. "coxxre" is an invalid ulimit type.

$ cat /etc/docker/daemon.json
{
    "default-ulimits": {
         "coxxre": {
             "Name": "coxxre",
             "Soft": 1024,
             "Hard": 2048
        }
    }
}

2. Start the docker service. Service started successfully.

$ systemctl restart docker
$ systemctl status docker
● docker.service - Docker Application Container Engine
   Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
   Active: active (running) since Mon 2019-11-25 19:57:12 CST; 5s ago
     Docs: https://docs.docker.com
 Main PID: 29960 (dockerd)
    Tasks: 37
   Memory: 41.7M
   CGroup: /system.slice/docker.service
           └─29960 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

3. Stop the docker service. Then, start docked in the following ways, but docked fails to start.

$ dockerd --default-ulimit coxxre=1024:2048
Status: invalid argument "coxxre=1024:2048" for "--default-ulimit" flag: invalid ulimit type: coxxre
See 'dockerd --help'., Code: 125

Describe the results you received:
As shown above.

Describe the results you expected:
Perhaps, the best result is that docker service fails to start (similar to docked flag) when the invalid ulimit is set in the daemon.json,

Output of docker version:

# docker version
Client: Docker Engine - Community
 Version:           19.03.5-rc1
 API version:       1.40
 Go version:        go1.12.12
 Git commit:        3e40132
 Built:             Wed Nov  6 07:29:27 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          19.03.5-rc1
  API version:      1.40 (minimum version 1.12)
  Go version:       go1.12.12
  Git commit:       3e40132
  Built:            Wed Nov  6 07:28:04 2019
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v1.2.8
  GitCommit:        a4bc1d432a2c33aa2eed37f338dceabb93641310
 runc:
  Version:          029124da7af7360afa781a0234d1b083550f797c
  GitCommit:        029124da7af7360afa781a0234d1b083550f797c
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683