dracut mangles the spl_hostid parameter

[dajhorn]

dracut/90zfs/parse-zfs.sh incorrectly sets the /etc/hostid file like this:

 # Let the command line override our host id.
 spl_hostid=`getarg spl_hostid=`
 if [ "${spl_hostid}" != "" ] ; then
         info "ZFS: Using hostid from command line: ${spl_hostid}"
         echo "${spl_hostid}" > /etc/hostid
 elif [ -f /etc/hostid ] ; then
         info "ZFS: Using hostid from /etc/hostid: `cat /etc/hostid`"
 else
         warn "ZFS: No hostid found on kernel command line or /etc/hostid.  "
         warn "ZFS: Pools may not import correctly."
 fi

This is incorrect because /etc/hostid is a binary file and the ${spl_hostid} kernel parameter is usually a hexadecimal string.

Currently, if spl_hostid=0x12345678 is set as a kernel parameter, then the module gets $spl_hostid[2..3], which is only eight bits of actual uniqueness. It follows that the value cannot be reversed for comparison against a generated gethostid() result, which could cause side-effects for issue #398.

The scripting contortion in commit openzfs/spl@79593b0 is required for all 32-bits of the value to be usable.

[behlendorf]

dajhorn do you have any objections to me moving the openzfs/spl@79593b0 change from the spl %post in to the zfs dracut/90zfs/module-setup.sh script. This needs to be done to resolve issue described in comment #98. I can update parse-zfs.sh as described in this issue while I'm at it.

[dajhorn]

No objections.