Locking a file backed mdconfig into memory

[Garrett Cooper]

On Fri, May 28, 2010 at 2:58 PM, Jeremy Chadwick
<freebsd at jdc.parodius.com> wrote:
> On Fri, May 28, 2010 at 12:26:12PM -0700, Dave Hayes wrote:
>> Jeremy Chadwick <freebsd at jdc.parodius.com> writes:
>> > And I think you meant this for variable names, in addition to what
>> > vfs.root.mountfrom should be (specific to RELENG_8):
>> > mfsroot_load="YES"
>> > mfsroot_type="mfs_root"
>> > mfsroot_name="/some/path/mfsroot"
>>
>> I'm using RELENG_7, but it seems rootfs_* works just like mfsroot_* ...
>> is the former deprecated?
>
> I spent a small bit of time looking through both RELENG_7 and RELENG_8
> source (/usr/src) as well as /boot (for the Forth portion) and I was
> unable to find any reference to "rootfs" aside from actual variable
> names (not loader variables) in C code or include files.  None were
> strings.  There's a strong possibility I'm not looking the right way
> (grep -ri ...).

I vaguely remember reading about rootfs in the past, but it's
definitely mfs_root now.

This is how I do it in my quickie loader.rc:

include /boot/loader.4th
set vfs.root.mountfrom="ufs:/dev/md0"
load /kernel
load -t mfs_root /mfsroot
start

> I can assure you that mfsroot_xxx works on both platforms because I
> wrote the below documentation:
>
> http://jdc.parodius.com/freebsd/pxeboot_serial_install.html
>
>> > vfs.root.mountfrom="ufs:/dev/md0"
>>
>> Hm, 'ufs:md0' currently works. What trouble can be had from using
>> the abbreviated device name?
>
> I have no idea; probably none.  This is just the first time I've seen
> the variable set to something "shorthand".  I would have to review
> the parser code to see how it works.

All depends on how you create the mfsroot. makefs(8) style mfsroots
for instance are like /dev/md0a blah.

It also depends on your version of FreeBSD IIRC, because (again IIRC)
GEOM changed the status quo in either 7.x or 8.x as to how md(4)
devices represented. Again, this is IIRC :P!

HTH,
-Garrett