Date: Tue, 21 May 2002 14:44:47 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Robert Watson <rwatson@freebsd.org> Cc: Maxime Henrion <mux@freebsd.org>, arch@freebsd.org Subject: Re: a virtual fs to allow root mounting of any fs without special code Message-ID: <3CEABFCF.35B80817@mindspring.com> References: <Pine.NEB.3.96L.1020521172613.79313X-100000@fledge.watson.org>
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Robert Watson wrote: > > You need to do exactly what you said you don't want people doing, in > > order to achieve proper jails that are indistinguishable by way of the > > root mounts. > > What I'm saying is that if it's a limited-purpose file system that doesn't > follow the normal conventions for vnodes and their relationship to a > struct mount, we need to prevent people from mis-using the file system, as > it will violate existing code assumptions about the presence of a struct > mount under certain circumstances. If we would like people to be able to > mount it just about anywhere following boot (as with any other synthetic > file system), we'll need a heavy-weight struct mount, which rootfs > currently doesn't have. I think if it's integrated, it needs a "struct mount". Personally, I'd like to see the "real" root union mounted over it. > That said, I'm not sure what you're saying applies. There's nothing > special about "rootfs" itself, it's pretty minimalist, what's special > about it is that it gives you a place to stick devfs during the bootstrap > (etc) so that you can get rid of special mountroot mounting procedures for > other file systems. I.e., the magic in Maxime's patch is in the > general-purpose root mounting case in the boot code, not in rootfs itself. I was really torn on this patch, so I didn't say anything previously: it implements part of one of my suggestions, but it tends to encourage people to not implement the correct solution to root vs. non-root mounting, since it offers a workable workaround to doing the right thing (seperating the mount-into-mountlist from the mount-into-fs-hierarchy is the cannonically correct approach). Now that you've implied the very thing I feared, I guess I need to say something. I would be really unhappy if the mount during boot ended up being significantly different than the mounting after boot. 8-(. There really needs to be a new VFSOP "MOUNTEDON", used to set the "last mounted on" information, which is the main difference (from an FS perspective) between root and non-root mounts. The vnode overlay is also a difference, but it's really obvious how this could be handed in an FS independent manner in higher level FS independent code (this is where the mount-into-fs-hierarchy should be done). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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