Date: Wed, 06 Jul 2011 16:55:36 -0700 From: Colin Percival <cperciva@freebsd.org> To: gibbs@freebsd.org Cc: "freebsd-xen@freebsd.org" <freebsd-xen@freebsd.org> Subject: Re: breakage in blkfront with ring_pages > 1 Message-ID: <4E14F5F8.7080108@freebsd.org> In-Reply-To: <4E14E7D2.9040708@FreeBSD.org> References: <4DF18EE5.5090704@freebsd.org> <4DF27EFF.5060005@FreeBSD.org> <4E13B6E9.9070202@freebsd.org> <4E13C2A4.5040202@FreeBSD.org> <4E13CB8F.8000009@freebsd.org> <4E13E111.9070005@freebsd.org> <4E14E7D2.9040708@FreeBSD.org>
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On 07/06/11 15:55, Justin T. Gibbs wrote: > On 7/5/11 10:14 PM, Colin Percival wrote: >> On 07/05/11 19:42, Colin Percival wrote: >>> Yep. Mess or not, shall I go ahead with having a loader tunable > control this, >>> or can you think of a better solution? >> >> Does anyone object to the attached patch? It keeps the differing > behaviour to >> a minimum -- we MUST set ring-ref with a FreeBSD blkback, and we MUST > NOT set >> it with a linux blkback -- but otherwise errs in the direction of > setting more >> variables than are needed, to maximize the possibility of a future blkback >> being compatible with both blkback_is_linux=0 and blkback_is_linux=1. > > It would be better to just change the FreeBSD blkback driver to be > compatible with the RedHat convention. Fine with me, but that will of course break compatibility between pre- and post- patch versions of FreeBSD. Aside from you, how many people use the FreeBSD blkback driver? > I'm still unclear on why the current FreeBSD blkfront driver believes > that it can use more than one page in your configuration given that the > RedHat blkfront doesn't advertise this capability in a way that the FreeBSD > blkfront understands (max-ring-pages isn'te set by blkback). Did you do > something to force blkfront to use more than one page? I'm seeing max-ring-pages set to 4. I don't know what tree EC2 is using on their Dom0 -- I've heard rumours that there's a lot of RedHat going on behind the scenes, but given Amazon's size it's entirely possible that they got a blkback which hasn't been released publicly. I'm sent an email asking where their blkback came from; I'll report back if/when I know something. -- Colin Percival Security Officer, FreeBSD | freebsd.org | The power to serve Founder / author, Tarsnap | tarsnap.com | Online backups for the truly paranoid
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