* John Baldwin <[EMAIL PROTECTED]> wrote: > On Friday 24 October 2008 12:50:12 am Ed Schouten wrote: > > * John Baldwin <[EMAIL PROTECTED]> wrote: > > > Perhaps have tty drivers sleep in detach until the tty is completely > > > gone? > > > Either that or free the unit number in the tty layer when the tty is > > > abandoned. > > > > Well, I could add a routine to the TTY layer that does that. The reason > > why the TTY layer is a little `lazy' with deallocating TTY unit numbers, > > is because I want to be absolutely sure processes agree they do not use > > the TTY (device name) anymore. > > > > I'll see if I can add a sleepable tty_gone() routine one of these days. > > I think what you want then is for the detach() routines to block until the > tty > is fully drained. This is similar to what we do for other places > (ether_ifdetach() is supposed to sleep until the ifnet is completely > unreferenced from userland for example (it may not fully ensure this yet, but > that is the way the driver should use the API, the driver can't possibly > close that sort of race in its own code). > > Actually, detach() _needs_ to block because when you kldunload a driver, once > detach() returns the code segment for that module can be unmapped. If there > are threads in that driver's tty routines still then you can get kernel page > faults.
Yes. That's true, but the reason why I implemented the way it is right now, is because the current behaviour is *very* pleasant to implement things like pts(4). There is no blocking inside the close() path of a pseudo-terminal master device (which makes no sense) and the tsw_free routine just returns the unit number back to the unrhdr (see ptsdrv_free() in sys/kern/tty_pts.c). But as I said, I will add a routine which does this. Apart from that, drivers could already implement the sleeping themselves, by just sleeping on a conditional variable until tsw_free() has been called. But it's easier to provide a proper routine to do this. -- Ed Schouten <[EMAIL PROTECTED]> WWW: http://80386.nl/
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