When requesting information about the daemon's configuration through the `/info`
endpoint, missing features (or non-recommended settings) may have to be presented
to the user.
Detecting these situations, and printing warnings currently is handled by the
cli, which results in some complications:
- duplicated effort: each client has to re-implement detection and warnings.
- it's not possible to generate warnings for reasons outside of the information
returned in the `/info` response.
- cli-side detection has to be updated for new conditions. This means that an
older cli connecting to a new daemon may not print all warnings (due to
it not detecting the new conditions)
- some warnings (in particular, warnings about storage-drivers) depend on
driver-status (`DriverStatus`) information. The format of the information
returned in this field is not part of the API specification and can change
over time, resulting in cli-side detection no longer being functional.
This patch adds a new `Warnings` field to the `/info` response. This field is
to return warnings to be presented by the user.
Existing warnings that are currently handled by the CLI are copied to the daemon
as part of this patch; This change is backward-compatible with existing
clients; old client can continue to use the client-side warnings, whereas new
clients can skip client-side detection, and print warnings that are returned by
the daemon.
Example response with this patch applied;
```bash
curl --unix-socket /var/run/docker.sock http://localhost/info | jq .Warnings
```
```json
[
"WARNING: bridge-nf-call-iptables is disabled",
"WARNING: bridge-nf-call-ip6tables is disabled"
]
```
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
