x/sys/unix: add consts, structs and ioctl calls from `<mtd/mtd-user.h>`

[lhl2617]

What did you expect to see?

It would be convenient to have MTD user space constants, utils and ioctl operations in the package.
An example use case is in Facebook's OpenBMC repo here.

The proposed addition entails:

• Adding #include <mtd/mtd-user.h> in unix/mkerrors.sh with the sufficient regex changes
• Adding #include <mtd/mtd-user.h> in unix/linux/types.go with the necessary bindings (C.struct_XXX for structs, constants for enum)
• Adding the necessary ioctl functions in unix/ioctl.go for unique types.

[gopherbot]

Change https://golang.org/cl/318211 mentions this issue: x/sys/unix: add consts, structs and ioctl calls for <mtd/mtd-user.h>

[lhl2617]

According to @robpike in #14873:

My point is that I don't want to see ioctl get helpers to make it look nice. It really doesn't need int and uint and *Termio and *Whatever helpers. The caller can do the conversion. It may be uglier but it will actually be faster, and anyway ioctl is hideous and I prefer not to hide that fact.

If necessary I will back off the ioctl functions change in unix/ioctl.go and leave the conversions to the caller. Opinions?

[ianlancetaylor]

For better or for worse, I think that golang.org/x/sys/unix has clearly gone in a different direction since Rob's comment from five years ago.

[robpike]

Oh, worse. Yes, worse.

[lhl2617]

I've backed out the ioctl wrappers in
https://go-review.googlesource.com/c/sys/+/318211/

I'll be happy to maintain another package using these structs and constants--easier and better to not further pollute x/sys

[ianlancetaylor]

This doesn't need to be a proposal. It's fine to add constants and types from system header files to x/sys/unix without writing a separate proposal for each set.