Subject: Changes to if_media for sysinst on NetBSD/sparc 1.4
To: None <,>
From: David Brownlee <>
List: tech-net
Date: 04/29/1999 10:12:58
	I have sysinst working on sparc, bar 'media selection' on an ss2.
	sysinst tries 'ifconfig le0 ... media 10base5', which fails.	
	10base5 is the only supported media, so from a user perspective
	this _should_ work, albeit being a NOP.

	I'd like to get a fix under the wire for 1.4 - help needed.
	Some options at the end - my preferred option would be b) or c).

    Details: (what I believe is happening)
	Lance init call ifmedia_set() which sets sc->sc_media->ifm_cur to
	the appropriate ifmedia_entry *, but leaves sc->sc_media.ifm_media
	(the user selected media word) at 0.

	'ifconfig le0 media 10base5' calls SIOCSIFMEDIA ioctl() which
	passes the media word to ifmedia_ioctl(), which makes the
	following check to see if it needs to take action:

	    if ((IFM_SUBTYPE(newmedia) != IFM_AUTO) &&
		(newmedia == ifm->ifm_media) &&
		(match == ifm->ifm_cur))
		    return 0;

	The first and third checks are OK, but the second check fails because
	newmedia==0x25, while ifm->ifm_media is still 0 from the init routine.

	ifmedia_ioctl() then calls ifm->ifm_change (lance_mediachange())
	which performs:

	    if (sc->sc_mediachange)
		    return ((*sc->sc_mediachange)(sc));
	    return (EINVAL);

	Since sc->sc_mediachange is not set by leattach_sbus() in if_le.c,
	we fail with EINVAL and sysinst chokes.
    Some options:
     a) Implement sc->sc_mediachange in if_le.c which does nothing but
	return success. Easy, but duplicated code in all single media
	drivers, and feels wrong.

     b) Change the check in ifmedia_ioctl() from 
	    (newmedia == ifm->ifm_media)
	    (ifm->ifm_media == 0 || newmedia == ifm->ifm_media)

	This fixes my case, but would change the behaviour for drivers
	that support multiple media, when the first SIOCSIFMEDIA ioctl()
	re-selects the default media (ifm->ifm_change would not be called).

     c) Same as b), except only affect drives with only one media type:
	    (newmedia == ifm->ifm_media || (ifm->ifm_media == 0 &&
	    LIST_NEXT(ifm->ifm_list.lh_first,ifm_list)==0)) &&
	Only affects single media drivers, and a media change on a single
	media driver _should_ be a NOP. I can't find a cleaner way to
	check for a single media driver in ifmedia_ioctl().

     d) Modify sysinst to not set media if only one media supported


	"You think you're God's gift to the opposite sex"
	"Maybe... if you believe in a malevolent God."