[ZFS][PATCH] Read-only root file system prevents SPA

[grarpamp]

Justin, et al...

>From a user perspective, sounds great!

Always thought the cachefile was a pain. For example, some systems
use encrypted pools, for which ZFS is rightly unaware of them until
the cleartext devices are attached. ZFS SPA's attempts to manage
it early in the process were annoying too.

On lots of machines, the root fs (/) is read-only from power on.
If a cache is desired, the cachefile parameter is set to either a
tiny ufs state partition or mfs. Or /boot/zfs is mounted on the
either of same via fstab. If not, cachefile=none :) zpool import
-a still works regardless of the cache because it tastes all the
devices, including CD-ROM's, heh. Works for me.

With the configuration on disk as a design feature of ZFS, I'm not
really sure of the need for a cachefile anyways. Other than maybe
to limit tasting for a specific pool to select devices. Or having
the kernel automagically do the zpool import -a (actually whatever
subset of pools was in use previously) part for you on boot.

BTW, there is no "zfs import" command. Nor is there a plain "zpool
import" that does an import without further arguments. Though it
does do the tasting and listing.

And I'm not sure if, as with the un-writeable case, setting
cachefile=none would also erroneously prevent needed events from
occuring. If so, that should be fixed as well.

Having vfs.zfs.ccw_retry_interval=0 meaning 'never update' would
be fine.