Messages in this thread | | | Date | Sun, 25 Mar 2012 23:33:15 +0100 | From | Al Viro <> | Subject | Re: TTY: tty_port questions |
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On Sun, Mar 25, 2012 at 10:06:10PM +0100, Alan Cox wrote: > Serial had pre-exising gunge not all of which has been cleaned, just as > it still has its own buffers that want to be using kfifo. > > Best examples are probably USB serial and neatest may well be the sdio > serial card driver.
Umm... So we have * tty_port created for each physical device, index assigned to it and tty_register_device() done to create sysfs junk/kick udev/etc. * TTY layer allocates tty on demand (open() time) and feeds them to ->install(), which is where we associate the suckers with tty_port, grabbing a reference to the latter and shoving it into ->driver_data (OK, it or that to struct it's embedded into - all the same) * ->cleanup() is called when TTY layer decided to free tty; drops a reference to port. Nobody will see that tty_struct anymore. * port outlives tty; over the lifetime of the latter associated port remains the same. * ->open()/->close()/->hungup() simply call tty_port_...() [BTW, is there any reason why you do not set ->driver_data to port and use container_of() in the places that want other parts of containing struct? That way you wouldn't need those wrappers at all and while ->write() is certainly called more often, there's no extra cost - compiler is able to figure out that local variable remains equal to argument-constant and turn accesses relative to it into ones relative to argument] * guts of opening the damn thing go into ->activate(), guts of stopping - into ->shutdown(). * removal does tty_unregister_device() + prevents ->install() from finding it + (under port->mutex) does tty_hangup() on associated tty (if any). BTW, I really don't like the look of that place - tty_hangup() is async (otherwise it'd deadlock instantly), so what the devil is protecting tty from being freed before __tty_hangup() is done with it? And when should the actual channel be killed? It appears to be done right after tty_hangup() returns, but since the actual work done by it is async... why is that safe? * ->activate() plays strange games with TTY_IO_ERROR; why do we bother, seeing that it's under port->mutex and anybody trying to open the same tty will wait anyway?
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