I noticed while researching bug #14555 that fd.c contains two separate
cases like
vfdP->seekPos = lseek(vfdP->fd, (off_t) 0, SEEK_CUR);
Assert(vfdP->seekPos != (off_t) -1);
This seems, um, unwise. It might somehow fail to fail in production
builds, because elsewhere it's assumed that -1 means FileUnknownPos,
but it seems like reporting the error would be a better plan.
regards, tom lane