proposal: x/sys/unix: make withData public

[leongross]

Proposal Details

The ifreq functionality through the Ifreq interface and its IoctlIfreq interface currently do not offer the flexibility it could have.
A simple example would be to issue some ioctl where ifr should be a pointer.
There are of course workarounds for that (e.g. issuing raw ioctls via the syscall API and providing a byte slice) but adding a more robust interface like already supposed would be a good idea.
I currently don't see any reason why not to expose this already existing functionality, but maybe I miss a bigger structural point here.

If you do not have enough resources for implementing this change I'd be happy to help you out on that.

The code suggests that @mdlayher once thought about exporting access to IfreqData, but postponed it due accessibility through IoctlGetEthtoolDrvinfo. This although is read only.

[mdlayher]

To clarify: what are you trying to do? IIRC my intent was to avoid exposing an unsafe.Pointer in the API, in favor of exposing type-safe wrappers for each type we need.

[leongross]

I want to issue an ioctl call that passes as an argument an Ifreq struct that holds custom ifr data that is a uintptr. The API calls for Ifreq although only expose methods to SetInet4Addr, SetUint16, SetUint32, none of which is suitable to set a pointer value (64bit) for https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/if.h#L253.

Alternatively, one could add an interface to set 64bit values or even arbitrary byte slices to ifr.raw.Ifru.

[mdlayher]

A pointer to what struct exactly? Is there a concrete C struct we can generate to give you a type safe API for this?