Multipath devnode blacklist

hi all,

there�s one thing i dont understand ...

in the file /etc/multipath.conf, why do we incluide "dm-" ??? a device mapper dm- is not supposed to be a multipath part that will be used after configuring mutipath dm??

devnode_blacklist {
        devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
        devnode "^hd[a-z]"
        devnode "^cciss!c[0-9]d[0-9]*"
        devnode "^sd[a-z]"