Date: Sat, 25 Feb 2012 11:23:00 -0700 From: Ian Lepore <freebsd@damnhippie.dyndns.org> To: Juergen Lock <nox@jelal.kn-bremen.de> Cc: freebsd-stable@freebsd.org Subject: Re: geom vs. removable disks/cards (was: Re: random problem with 8.3 from yesterday) Message-ID: <1330194180.7317.64.camel@revolution.hippie.lan> In-Reply-To: <201202250655.q1P6tiSU015359@triton8.kn-bremen.de> References: <201202221334.36484.erich@alogreentechnologies.com> <64FF3DF7-6EEA-480D-85AA-5784AF013EA8@lassitu.de> <201202241350.56933.erichfreebsdlist@ovitrap.com> <1330100633.7317.41.camel@revolution.hippie.lan> <4F4811B4.4000701@FreeBSD.org> <201202250655.q1P6tiSU015359@triton8.kn-bremen.de>
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On Sat, 2012-02-25 at 07:55 +0100, Juergen Lock wrote: > In article <1330126840.7317.60.camel@revolution.hippie.lan> you write: > >On Sat, 2012-02-25 at 00:39 +0200, Andriy Gapon wrote: > >> on 24/02/2012 18:23 Ian Lepore said the following: > >> > I've always > >> > suspected something in the geom layer isn't noticing that a CF or SD > >> > card in the reader got removed/inserted/reformatted, and un-/re-plugging > >> > the whole reader (making the cam layer destroy and recreate the devices) > >> > makes geom aware of the change. > >> > >> This is a fact, actually. Nothing in GEOM layer (and below it) notices a silent > >> card change, since most hardware doesn't have any notification for the change > >> and FreeBSD disk stack doesn't do any polling for changes. > >> > > > >If the hardware did have change notification, is there a mechanism that > >would communicate that to geom? That's a precursor question to my real > >question: is there a way to manually kick geom when necessary? If the > >api exists but there's no userland app to make the needed calls, I'll > >write some code -- just point me at a manpage or header file. > > scsi has a mechanism called unit attention to report things like > media changes, not sure usb devices use that tho since the host can > only poll them... > > Anyway, the usual workaround is to force a geom retaste by opening > the device for writing without actually writing anything, e.g.: > > # : >/dev/da0 > > Btw this can't be Erich's problem I'd say since he said he's > plugging in a thumbdrive not a card into a reader (and also writing > /dev/zero to it) so geom _should_ already taste it. (Unless the > write fails since the thumbdrive is too slow initializing or something > like that...) > > HTH, > Juergen I was a bit concerned that the similarities between Erich's symptoms and mine were purely superficial, with different underlying causes. I've never seen the stale geom data problem I described on a thumb drive, except when I've used dd to zero out the beginning of a drive that was gpt-formatted but left the backup partition table at the end of the drive -- that always causes me problems that only get fixed by using gpart destroy -F. Thanks for the tip about forcing a re-taste, I think I'll be using that a bunch. -- Ian
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