I am using MBed OS in a very controlled environment, where every device has its own static IP address. Furthermore there are rather tight restrictions on the application size, so I am looking into reducing the size of the final binary as much as possible.
When looking at the map file I noticed that the DNS part of the ethernet stack does use quite a lot of room. I don’t need DNS, as outlined above, so I had a look into disabling it. As far as I can tell there is no way of doing it other than editing the LWIP options and part of the LWIPInterface class.
Question: Is there a easier way of disabling DNS in the LWIP stack or MBed OS in general? Was this use-case considered at any point?
Further Info: I am currently using Mbed Os 6.2 with the corresponding mbed-cli tools. The development boards I use are the NUCLEO-L552ZE-Q with an external EMAC and the NUCLEO-H743ZI, although other NUCLEO boards are available and could be tested.
I’m afraid disabling DNS operations is not implemented at the moment. If you want to disable it in the LWIP stack, you have to fiddle with liwoptsh and turn it off: #define LWIP_DNS 0 (line 195). As you noted part of the LWIPInterface class have to be modified. To reclaim the most byte out of that change I would also suggest providing conditional guard to the mbed::DNS class. Some changes have to be propagated up to the socket, for example, sendto use gethostbyname.
If you intend to modify your source tree to accommodate such scenario I would suggest opening a pull request in mbed-os repository. We can help you there with the change and it would be committed durably into Mbed OS.
thanks for your input. Currently I am looking for other places where I can restrict the app size. This is mostly due to the many changes you already hinted at.
However I guess at some point I will try to implement this. Thank you for showing the way on how to do this.
