Date: Tue, 6 Jan 2015 14:50:28 -0800 From: Eric Joyner <erj@erj.cc> To: mike@karels.net Cc: Adrian Chadd <adrian@freebsd.org>, Rui Paulo <rpaulo@me.com>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Eric Joyner <erj@erj.cc>, John Baldwin <john@baldwin.cx>, Jack Vogel <jfvogel@gmail.com>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: Adding new media types to if_media.h Message-ID: <CA%2Bb0zg9ZiGiVQvLyOmO40_8qwtLU1z3RPW4xjZ16qTQcXZAEPA@mail.gmail.com> In-Reply-To: <201412130106.sBD16tgl072730@mail.karels.net> References: <2116096.l1vR0RuKRU@ralph.baldwin.cx> <201412130106.sBD16tgl072730@mail.karels.net>
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Then going with what Mike says about leaving backwards compatibility, I suppose we should do something like what Adrian suggested, and add a separate struct. We can indicate that the separate struct exists by setting the media type value in the if_media word to 0xc0, since that's the last unused value. Then existing programs won't have to support any new features if they don't want to. Adrian -- where can I look for more information on what net80211 does for media types? Do you mean what it does with MCS values, or something more; I've looked at it a bit, but I don't know very much about how Wi-Fi works. - Eric On Fri, Dec 12, 2014 at 5:06 PM, Mike Karels <mike@karels.net> wrote: > > On Friday, December 12, 2014 12:26:24 PM Jack Vogel wrote: > > > I think I'd go along with Mike, keeping it simpler seems like a good > idea. > > > > > > Jack > > > If the userland ABI impact isn't too broad I think this is fine. Mike, > do you > > know off hand how many user-facing things would be affected? > > I didn't know off hand, but I have a glimpse index at $WORK (it's for > McAfee > Firewall Enterprise, aka Sidewinder, based on 8.2). I found 45 references > to > if_media.h at user level, including "ports" that we use, and excluding our > own software. The list includes libpcap, snmpd, dhclient, quagga, xorp, > atm, devd, and rtsold. fwiw, I found about 260 inclusions of if_media.h > in the kernel. > > This suggests that we should preserve a backward-compatible user API, even > if it has limits. Unfortunately, the media word I mentioned is a plain > int, > not a typedef. I would propose a similar API that is not limited, but easy > to convert (e.g. using a new typedef). I'd be willing to sketch out > something > like that. > > > > On Fri, Dec 12, 2014 at 6:39 AM, Mike Karels <mike@karels.net> wrote: > > > > > Any other thoughts, or should I start looking at seeing what I can > take > > > > > copy from net80211? > > > > > > > > > > Also adding -net, since this is pretty relevant. > > > > > > > > I had the same reaction as Adrian initially, as an int with numerous > > > > fields > > > > seems really messy. However, I don't think we have the challenges of > > > > 802.11, > > > > and the only real problem is that the subtype field has run out of > bits. > > > > And both ifconfig and the drivers are cast in the form of a scalar > "media > > > > word", with parameters to ifmedia_add like IFM_ETHER | IFM_1000_T | > > > > IFM_FDX > > > > (assuming that all the bits are in a scalar). > > > > > > > > Instead, I would propose that we simply change the media word from > 32 bits > > > > to 64, and move the subtype from its current location to a new field > (e.g. > > > > 16 bits) in the new space. I believe this can be KPI compatible, > and it > > > > is relatively easy to provide a backward-compatible ABI. There > should be > > > > a reserved subtype for "other" that can be encoded in the existing > field > > > > for use when the subtype can't fit in the old field. This seems much > > > > easier, > > > > can be KPI compatible, and will make it much easier to backport > drivers. > > > > A backport could simply define the new subtypes as "other", and the > KPI > > > > would still be compatible. > > > > > > > > Thoughts? > > > > > > > > Mike > > > -- > > John Baldwin > > Mike >
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