Date: Fri, 12 Dec 2014 19:06:55 -0600 From: Mike Karels <mike@karels.net> To: John Baldwin <john@baldwin.cx> Cc: Adrian Chadd <adrian@freebsd.org>, Rui Paulo <rpaulo@me.com>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Eric Joyner <erj@erj.cc>, Jack Vogel <jfvogel@gmail.com>, freebsd-arch@freebsd.org Subject: Re: Adding new media types to if_media.h Message-ID: <201412130106.sBD16tgl072730@mail.karels.net> In-Reply-To: Your message of Fri, 12 Dec 2014 15:31:06 -0500. <2116096.l1vR0RuKRU@ralph.baldwin.cx>
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> 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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