Date: Wed, 26 Apr 2000 15:28:52 -0400 (EDT) From: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> To: "C. Stephen Gunn" <csg@waterspout.com> Cc: Archie Cobbs <archie@whistle.com>, freebsd-net@FreeBSD.ORG, luigi@FreeBSD.ORG, remy@boostworks.com, pavel@alum.mit.edu, nsayer@sftw.com, juliam@elischer.org Subject: Re: Proposal for ethernet, bridging, netgraph Message-ID: <200004261928.PAA44573@khavrinen.lcs.mit.edu> In-Reply-To: <20000426011134.A768@waterspout.com> References: <20000425164027.A2553@waterspout.com> <200004260003.RAA55104@bubba.whistle.com> <20000426011134.A768@waterspout.com>
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<<On Wed, 26 Apr 2000 01:11:34 -0500, "C. Stephen Gunn" <csg@waterspout.com> said: > Like Garrett said, apparently some Ethernet hardware (the "better" > cards mind you) can DMA to any address, others can only do it on > 16-bit or 32-bit boundaries, hence the flaming hoops. 16-bit is not a problem (unless some loser invents a link layer with odd-length headers). 32-bit is a problem, for the reasons which have already been developed. > From reading the code, the driver doesn't have to operate this way. > It just allocates an ether_header seperate from the mbuf chain. This > data could be in the mbuf (with some alignment haggling) with very > little drop in performance. Speaking as the perpetrator of that driver (although I will disclaim all knowledge if you ask me questions), I probably did that because I didn't know anything at the time about writing network interface drivers (or indeed UNIX device drivers at all). -GAWollman -- Garrett A. Wollman | O Siem / We are all family / O Siem / We're all the same wollman@lcs.mit.edu | O Siem / The fires of freedom Opinions not those of| Dance in the burning flame MIT, LCS, CRS, or NSA| - Susan Aglukark and Chad Irschick To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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