Date: Tue, 29 Sep 2009 14:12:56 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: xcllnt@mac.com Cc: marcel@freebsd.org, jhb@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, rwatson@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r197608 - head/sys/geom/part Message-ID: <20090929.141256.-981704958.imp@bsdimp.com> In-Reply-To: <EF993D67-F575-45CC-98EC-A1163EF15B50@mac.com> References: <1F22EA6A-2793-45CE-9669-3FFD550CF4E2@mac.com> <alpine.BSF.2.00.0909291759180.94746@fledge.watson.org> <EF993D67-F575-45CC-98EC-A1163EF15B50@mac.com>
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In message: <EF993D67-F575-45CC-98EC-A1163EF15B50@mac.com>
Marcel Moolenaar <xcllnt@mac.com> writes:
:
: On Sep 29, 2009, at 10:00 AM, Robert Watson wrote:
:
: >
: > On Tue, 29 Sep 2009, Marcel Moolenaar wrote:
: >
: >>> Why do you check for zeros at all? AFAIK, the only real check is
: >>> for AA55 at the end of the sector (and having an MBR or other
: >>> Extended MBR partition entry point at the sector in question).
: >>> The '96' thing seems rather arbitrary in the code, and I think the
: >>> zero's check is overly restrictive.
: >>
: >> Only checking for a signature that 99% of the boot blocks have
: >> isn't enough. The msdos file system has that signature and the
: >> check for all-zeroes is to prevent false positives there.
: >
: > And, as I recall, the msdosfs check has been gradually getting
: > weaker over time as the constraints it places on things like
: > cylinder counts become obsolete. It's not quite that we'll mount
: > msdosfs on any random pile of bytes, but it might be getting there...
:
: We really need to get to a point where we treat partition types
: seriously and
: use it to help avoid false positives. Reducing or eliminating false
: positives
: is critical if we ever want to go towards DWIM or auto-mounting. With
: the
: partition type taken into consideration, we may be able to eliminate
: ad hoc
: checks, like the zero check in g_part_ebr, without creating false
: positives.
Part of the problem too is that the msdosfs code checks too many
things, making it hard to use on raw images :( Of course, I'm about
12 sigma from the mean on the images I use, but still...
Warner
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