Can I use a (modified) LGPL-2.1 library in my MIT-licensed library?

Question

I am developing a Modbus library for use on microcontrollers.

Internally, I am using an (apparently) heavily-modified version of libmodbus (slightly-modified from the version that comes with ArduinoModbus) and a slightly-modified version of ArduinoRS485.
Both of these libraries are licensed under LGPL-2.1.
They are stored under my src directory, and #included into my library's source files.

I assume, then, that this does not count as "linking to the library"? (only linking to the library makes you work exempt)
Which means that I have to license my entire library under LGPL-2.1 or 3.0?

I really don't like how restrictive the LGPL is, and I would prefer MIT.

Answer 1

As I read it, you are right, your library must be released under LGPLv2.1(+). You've based it squarely on the libmodbus code, which is indeed LGPLv2.1+, and by s2c you must release your modified version of the library under the same license.

I'm sorry you'd prefer to write an MIT-licensed library, but you chose to modify LGPL code, and so the old adage applies: if you want to get to there, don't start from here.