Date: Mon, 11 Oct 2010 09:46:42 +0200 From: =?iso-8859-1?Q?S=F8ren_Schmidt?= <soren.schmidt@gmail.com> To: Alexander Motin <mav@FreeBSD.ORG> Cc: sos@FreeBSD.ORG, FreeBSD-Current <freebsd-current@FreeBSD.ORG>, Pawel Jakub Dawidek <pjd@FreeBSD.ORG>, Andriy Gapon <avg@icyb.net.ua>, phk@FreeBSD.ORG Subject: Re: letting glabel recognise a media change Message-ID: <358D7DEF-4EEB-4E22-A251-DC383FF57BCD@gmail.com> In-Reply-To: <4CB22833.70304@FreeBSD.org> References: <4CA3BD7C.9080306@feral.com> <mailpost.1285845776.1043534.73790.mailing.freebsd.current@FreeBSD.cs.nctu.edu.tw> <4CA4CCE3.9060408@FreeBSD.org> <20101010155340.GQ1733@garage.freebsd.pl> <4CB22833.70304@FreeBSD.org>
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On 10/10/2010, at 22.55, Alexander Motin wrote: > Pawel Jakub Dawidek wrote: >> On Thu, Sep 30, 2010 at 08:46:11PM +0300, Alexander Motin wrote: >>> Andriy Gapon wrote: >>>> on 30/09/2010 01:28 Matthew Jacob said the following: >>>>> If something like that was in place, I assure you that things = would start to use >>>>> it very quickly. >>>> I am not sure about this. >>>> Because, e.g. I don't see an easy way to know that media is changed = in scsi_cd >>>> driver. That is, without polling. I don't consider polling to be = an easy way for >>>> a number of reasons. >>> SATA specification defines concept of Asynchronous Notification. It = is >>> already used by port multipliers to report about PHY events. It is = also >>> supposed to be used by CD drives to report media change. I haven't = seen >>> such devices yet, but hope they may appear sometimes. >>>=20 >>> And even without AN support it would be nice to implement proper >>> handling for SCSI "UA - media changed" errors within CAM. It still = won't >>> be perfect without using polling, but probably still something. >>=20 >> I'd like to know the original reason why CD device is represented by >> GEOM provider and not CD media. For my naive thinking CD media should = be >> GEOM provider that we taste once the media is inserted and orphan = once >> the media is removed. I don't see any reasons for CD device to be = useful >> GEOM provider, but maybe I'm overlooking something. >>=20 >> Poul-Henning or Soren, do you remember who made and why this design = choice? >=20 > SCSI drivers receive no notification on media insertion. Somebody = should > poll device. At this moment it is handled by consumers. Indeed not = sure > it is the best idea. If we want driver to bother with this polling - = we > may do as you propose. Actually in sdhci(4) driver I am doing this way = - > mmcsdX device appears when card inserted and disappears on removal. >=20 > I think first thing that may brake if there will be no cdX device - > loading the media with some commands. Also it may be non-intuitive = that > drive is present, but disk is not registered in GEOM. Think burning data on empty media. -S=F8ren "Any sufficiently advanced technology is indistinguishable from magic." --
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