Horrible ugliness in V.2 readi/writei.

[Phil Chadwick]

In article <150 at neology.OZ> chris at neology.OZ (Chris Maltby) says:

    >The problem turned out to be this
    >revolting code in the 5.2 readi/writei code:
    >
    >	if (cdevsw[major(dev)].d_tty != NULL)
    >	{
    >		tp = &cdevsw[major(dev)].d_tty[minor(dev)];
    >		(*linesw[tp->t_ldisc].l_write)(tp);
    >	}
    >	else
    >		(*cdevsw[major(dev)].d_write)(minor(dev));
    >
    >This part of the system has no right to assume what the code in a
    >driver's read/write routine does, even if it seems to be a tty driver.

Here, here!

I tripped over this some time ago while writing a pseudo dn11 driver.
Code put into the tty's write routine did nothing (not surprising -
once you realise it's being bypassed).  To the best of my recollection
it's been there since the very first System V release.

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