Date: Wed, 7 Apr 1999 08:54:35 +0930 From: Greg Lehey <grog@lemis.com> To: FreeBSD Hackers <hackers@freebsd.org> Subject: Separate boot partition? Message-ID: <19990407085435.M2142@lemis.com>
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One of the most asked-for features currently not implemented in Vinum
is to be able to have the root file system running under Vinum. It
looks simple enough, but there's a powerful chicken-and-egg problem in
there: the bootstrap doesn't run Vinum, so it can't read the kernel
from a Vinum volume. There is little provision to remount the root
file system elsewhere than where the bootstrap thinks it is, and since
by this time there are open file descriptors, it's difficult to change
this behaviour.
I've been thinking about this, and the best I can come up with is a
separate boot file system, like some System Vs do. In System V the
interest seems to come from the fact that the bootstraps are too
stupid to understand file systems such as VxFS, but basically they
just contain the kernel. I was thinking of additional information
such as the name of the root file system, though of course that could
be compiled into the kernel. The sequence would then be:
boot loads the kernel from /boot/kernel.
kernel initializes, including Vinum if desired, and
loads the root file system
The kernel data file is still available via a symlink from /kernel
to /boot/kernel, or as a copy somewhere.
Note that the original file from which the kernel is loaded is no
longer needed once the kernel was loaded. Some programs, such as ps,
may use the kernel file to extract information about the kernel, but
this doesn't have to be from the same file as from which the kernel
was loaded: the file just needs the same contents, so a copy would be
OK.
Comments?
Greg
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