similar patch has been in 4.x for a while, but is more hacky there.)
For this to work, vinum has to be loaded early (e. g. from
boot/loader), for obvious reasons. If the kernel env variable
(aka. loader variable) "vinum.autostart" is set, vinum then asks the
sysctl kern.disks for all available disks in the system, and scans
them for possible vinum headers.
For statically compiled kernels, this behaviour can be obtained even
without boot/loader by using "options VINUM_AUTOSTART" (though this is
not the recommended way).
Alternatively, the 4.x way to specify "vinum.drives" is also supported.
No further hacks (like the 4.x "vinum.root" variable) are needed,
since in 5.x, mountroot() asks back at the drivers to have them
resolve the name of the root FS into a dev_t (using the dev_clone
eventhandler).
(The MFC reminder below is for a partial MFC for vinum.autostart, the
rest is already there in 4.x.)
Timed out on: grog
MFC after: 2 weeks
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