zfsd should be able to online an L2ARC that disappears and returns
Previously, this didn't work because L2ARC devices' labels don't contain pool
GUIDs. Modify zfsd so that the pool GUID won't be required:
lib/libdevdctl/guid.h
Change INVALID_GUID from a uint64_t constant to a function that
returns an invalid Guid object. Remove the void constructor.
Nothing uses it, and it violates RAII.
cddl/usr.sbin/zfsd/case_file.h
cddl/usr.sbin/zfsd/case_file.cc
Allow CaseFile::Find to match a CaseFile based on Vdev GUID alone.
In CaseFile::ReEvaluate, attempt to online devices even if the newly
arrived device has no pool GUID.
cddl/usr.sbin/zfsd/vdev_iterator.cc
Iterate through a pool's cache devices as well as its regular
devices.
Reported by: avg