get error message on kvm descriptor
This function returns a string describing the most recent error condition on the
. The results are undefined if the most
library call did not produce an
error. The string returned is stored in memory owned by
so the message should be copied out and
saved elsewhere if necessary.
This routine cannot be used to access error conditions due to a failed
kvm_openfiles(3) call, since failure
is indicated by returning a
Therefore, errors on open are output to the special error buffer passed to
kvm_openfiles(3). This option is not
available to kvm_open(3).