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Re: [Xen-devel] [PATCH] xencons missing string allocation

On Fri, 2005-12-09 at 20:54 +0200, Muli Ben-Yehuda wrote:
> On Fri, Dec 09, 2005 at 11:37:31AM -0700, Alex Williamson wrote:
> > 
> >    I was trying to boot dom0 w/ "xencons=ttyS1 console=ttyS1".  It gives
> > some weird error messages:
> > 
> > Warning: dev (ttyS2) tty->count(2) != #fd's(1) in release_dev
> > Warning: dev (ttyS2) tty->count(3) != #fd's(1) in tty_open
> > 
> > And blows up with a page fault.  The page fault is because we don't
> > actually allocate a buffer for the tty driver name.
> Errr... the patch looks curious. Why does it work when ->name points
> to the heap but not when it points to the data segment? they should be
> equivalent and many tty drivers appear to set ->name to the data
> segment. Is something trying to modify xencons_driver->name later?

   You're right, I guess a lot of tty/char drivers seem to have the name
on the heap.  However, it would suggest there's a path where the name is
referenced outside of the context of that function since it prevents a
page fault.  I'll keep looking to make sure I'm not just getting lucky.

> (also, do you know why do we need the fugly DRV() macro in that code?)

   No idea, I'm not a fan either.  Thanks,


Alex Williamson                             HP Linux & Open Source Lab

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