One of the side effects of calling zvol_create_minors() in
zvol_init() is that all pools listed in the cache file will
be opened. Depending on the state and contents of your pool
this operation can take a considerable length of time.
Doing this at load time is undesirable because the kernel
is holding a global module lock. This prevents other modules
from loading and can serialize an otherwise parallel boot
process. Doing this after module inititialization also
reduces the chances of accidentally introducing a race
during module init.
To ensure that /dev/zvol/<pool>/<dataset> devices are
still automatically created after the module load completes
a udev rules has been added. When udev notices that the
/dev/zfs device has been create the 'zpool list' command
will be run. This then will cause all the pools listed
in the zpool.cache file to be opened.
Because this process in now driven asynchronously by udev
there is the risk of problems in downstream distributions.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #756
Issue #1020
Issue #1234
This rule does not need to be dracut specific. Automatically loading
the zfs module stack when a zfs device is detected is usually desirable.
My only concern is that this might cause trouble for large pools where
we don't want to automatically import the pool until all the disks are
available. However, we'll cross that bridge when we come to it.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Brian Behlendorf
Kyle Fuller