Date: Fri, 7 Oct 2011 16:37:38 -0400 From: Arnaud Lacombe <lacombar@gmail.com> To: Warren Block <wblock@wonkity.com> Cc: Garrett Cooper <yanegomi@gmail.com>, Glen Barber <gjb@freebsd.org>, Poul-Henning Kamp <phk@phk.freebsd.dk>, freebsd-current@freebsd.org, Benjamin Kaduk <kaduk@mit.edu> Subject: Re: aliasing (or renaming) kern.geom.debugflags Message-ID: <CACqU3MV2cMxRHuqLCk5wmETB%2B3_fpxt-nYz_zy9rdL%2BF-8oypg@mail.gmail.com> In-Reply-To: <alpine.BSF.2.00.1110071352210.2450@wonkity.com> References: <81477.1318015137@critter.freebsd.dk> <4E8F55CC.3060302@FreeBSD.org> <alpine.BSF.2.00.1110071352210.2450@wonkity.com>
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Hi, On Fri, Oct 7, 2011 at 4:27 PM, Warren Block <wblock@wonkity.com> wrote: > On Fri, 7 Oct 2011, Glen Barber wrote: > >> Hi, >> >> On 10/7/11 3:18 PM, Poul-Henning Kamp wrote: >>>> >>>> My guess is that GEOM isn't letting go of the GPT table and you have >>>> multiple partitions in the GPT table and you're not destroying them >>>> hierarchically in a proper manner.. but again, that's just a guess >>>> based on hazy recollection. >>> >>> If none of the GPT partitions are open, you should be able to >>> open /dev/da0. If not, the GPT geom class is buggy. >>> >> >> In my experience, without kern.geom.debugflags=16, the MBR will not be >> written to the memstick, leaving you with what would effectively be a >> coaster in the not-so-distant past. > > Tried it just now with the 9.0-BETA3 memstick image. > > # dd if=/tmp/FreeBSD-9.0-BETA3-amd64-memstick.img of=/dev/da0 bs=64k > 10463+1 records in > 10463+1 records out > 685731840 bytes transferred in 52.614157 secs (13033219 bytes/sec) > # mount /dev/da0p2 /mnt > # dd if=/tmp/FreeBSD-9.0-BETA3-amd64-memstick.img of=/dev/da0 bs=64k > dd: /dev/da0: Operation not permitted > # sysctl kern.geom.debugflags=16 > kern.geom.debugflags: 0 -> 16 > # dd if=/tmp/FreeBSD-9.0-BETA3-amd64-memstick.img of=/dev/da0 bs=64k > 10463+1 records in > 10463+1 records out > 685731840 bytes transferred in 52.915362 secs (12959031 bytes/sec) > in the mean time, some background application issued a sync(2), corrupting part of what you just wrote, if not crashing the kernel. > Followed by removing the memory stick without unmounting it to avoid > overwriting part of the image. No obvious problems, but no, it's not > polite. (I'm thinking "automounter" here.) > > We could make the normal procedure just the dd, followed by a note: > > If this gives an 'Operation not permitted' error, make sure that the > target device is not in use or being automounted by some helpful > utility program. > > And maybe > > If the error still appears and no other options are available, > sysctl kern.geomflags.debug=16 > will override the system safety and allow writes to the device. > Then you can start to introduce backdoor for every single kernel-enforced policy. `kern.geomflags.debug=16' should not be used by the lambda user. - Arnaudhelp
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