[tlbuild] dvi test?

[Karl Berry]

    When it tries to reread the first page of the dvi file after hitting
    'R', it reads a zero byte

Seems like the system has decided not to (re)open the real file, and
instead to return 0 0 0 0 0 ... as if one had seeked past the end or
some such. Or an earlier error has made the fd invalid. Or ... ?
It presumably has to be something in the OS operation.

Could add some code at the point of the reread (sorry, I don't know
where that is) to just read(2) some bytes and see what you get. I
predict all zeros.

Maybe running strace on the failing invocation (as minimum as possible
-- just the R) to see all syscalls would be of some help. -k