CHN_F_VCHAN_PASSTHROUGH
#define CHN_F_VCHAN_DYNAMIC (CHN_F_VCHAN_PASSTHROUGH | CHN_F_VCHAN_ADAPTIVE)
if (*vchanmode & CHN_F_VCHAN_PASSTHROUGH)
dflags = CHN_F_VCHAN_PASSTHROUGH;
parent->flags |= CHN_F_VCHAN_PASSTHROUGH;