Date: Fri, 16 Oct 2009 11:38:08 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Andriy Gapon <avg@icyb.net.ua> Cc: Alexander Best <alexbestms@math.uni-muenster.de>, freebsd-current@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org> Subject: Re: panic when mounting device >= 2 times Message-ID: <20091016083808.GO27077@deviant.kiev.zoral.com.ua> In-Reply-To: <4AD82F80.2050302@icyb.net.ua> References: <permail-2009101411215080e26a0b00001bea-a_best01@message-id.uni-muenster.de> <4AD5BD00.4050700@icyb.net.ua> <20091014204657.GB1727@garage.freebsd.pl> <4AD82F80.2050302@icyb.net.ua>
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[-- Attachment #1 --] On Fri, Oct 16, 2009 at 11:32:00AM +0300, Andriy Gapon wrote: > on 14/10/2009 23:46 Pawel Jakub Dawidek said the following: > > I've this patch that is suppose to fix it: > > > > http://people.freebsd.org/~pjd/patches/geom_vfs.c.patch > > > > But AFAIR its not complete. I think it is still possible to remount one > > of the read-only mounts to read-write. > > > > Another possibility that comes to my mind is to keep list/array of > > consumers in bo_private instead of using one consumer only. This would > > be better in terms of access management. > > This looks very good for at least preventing the most common accidents. > I've been thinking about something like creating a cloned vnode for the device > vnode and giving a private copy to each filesystem. But I currently lack a lot > knowledge in this area, so I can't even say if it could be feasible, let alone > implement it. I suspect this is pretty much bad idea. The reason is that buffer list is managed by buffer object that has 1:1 correspondence with the vnode. You will end up with aliased buffers. Actually, this could happen without the proposed change as well, I believe. It is enough to mount devfs several times and then use different devfs vnodes for the same device. But since people usually mount filesystems using /dev, this does not happen in practice. For multiple ro mounts to work, we need to find a way to push the buffer object to cdev. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEYEARECAAYFAkrYMPAACgkQC3+MBN1Mb4j9pACdFiiomSB6/hKkk81VuQ1ELERr Qz8AnAt3rNHt2F/URcnAsR9hO0+bIijn =oyl6 -----END PGP SIGNATURE-----help
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