From 513b032c98b4b9414aa4e9b4a315cb1bf0380101 Mon Sep 17 00:00:00 2001 From: George Spelvin Date: Sun, 10 Feb 2013 04:08:32 -0500 Subject: pps: Add pps_lookup_dev() function The PPS serial line discipline wants to attach a PPS device to a tty without changing the tty code to add a struct pps_device * pointer. Since the number of PPS devices in a typical system is generally very low (n=1 is by far the most common), it's practical to search the entire list of allocated pps devices. (We capture the timestamp before the lookup, so the timing isn't affected.) It is a bit ugly that this function, which is part of the in-kernel PPS API, has to be in pps.c as opposed to kapi,c, but that's not something that affects users. Signed-off-by: George Spelvin Acked-by: Rodolfo Giometti Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/pps/pps.c | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'drivers/pps') diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c index 2420d5af0583..a70e384262e5 100644 --- a/drivers/pps/pps.c +++ b/drivers/pps/pps.c @@ -352,10 +352,43 @@ free_idr: void pps_unregister_cdev(struct pps_device *pps) { + pps->lookup_cookie = NULL; device_destroy(pps_class, pps->dev->devt); cdev_del(&pps->cdev); } +/* + * Look up a pps device by magic cookie. + * The cookie is usually a pointer to some enclosing device, but this + * code doesn't care; you should never be dereferencing it. + * + * This is a bit of a kludge that is currently used only by the PPS + * serial line discipline. It may need to be tweaked when a second user + * is found. + * + * There is no function interface for setting the lookup_cookie field. + * It's initialized to NULL when the pps device is created, and if a + * client wants to use it, just fill it in afterward. + * + * The cookie is automatically set to NULL in pps_unregister_source() + * so that it will not be used again, even if the pps device cannot + * be removed from the idr due to pending references holding the minor + * number in use. + */ +struct pps_device *pps_lookup_dev(void const *cookie) +{ + struct pps_device *pps; + unsigned id; + + rcu_read_lock(); + idr_for_each_entry(&pps_idr, pps, id) + if (cookie == pps->lookup_cookie) + break; + rcu_read_unlock(); + return pps; +} +EXPORT_SYMBOL(pps_lookup_dev); + /* * Module stuff */ -- cgit v1.2.3