BTW curl does seem to do what i wrote above, for example `curl_easy_init` returns a `CURL` object on success or NULL if there was an error [1] and `curl_easy_perform` returns a `CURLcode` value [2] that looks like it is used across the API to indicate errors.
If you have a kernel function returning a pointer and you think that you're supposed to check for NULL when it actually returns a ERR_PTR in case of errors you will not only fail to do the check but on top of that end up with a garbage pointer somewhere in your program. If you have a MMU and you try to de-reference the pointer you'll have a violent crash, which at least shouldn't be too hard to debug. If you feed the pointer to some hardware module or if you're working on an MMU-less system then Good Luck; Have Fun.
C doesn't have your back here. It doesn't let you signal how a function reports errors, it doesn't even let you tag nullable pointers.
C error handling ergonomics are non-existent which means that everybody bakes ad-hoc library-specific conventions that are extremely error-prone.
You could argue that they're doing it wrong and you might have a point but if almost everybody gets it wrong maybe it's fair to blame the language itself a little bit.