sam/_libc.h has: OREAD = 0, OWRITE = 1, ORDWR = 2, OCEXEC = 4,
but it looks like nothing #includes that file, so perhaps that doesn't have to be patched. Have you tested sam on the Hurd? If these flags are sent in the Topen and Tcreate requests of the 9P protocol, then changing their values breaks compatibility between network hosts that run different implementations. Do the Debian packages support that protocol?