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authorGeorge Spelvin <linux@horizon.com>2013-02-10 04:08:32 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-02-13 09:40:35 -0800
commit513b032c98b4b9414aa4e9b4a315cb1bf0380101 (patch)
tree3483659abdcc63cb831bf9ded62e981de3ffd5e3 /drivers
parent6d53c3b71d32da665dc2742c1e8663741f27d3cd (diff)
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 <linux@horizon.com> Acked-by: Rodolfo Giometti <giometti@enneenne.com> Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/pps/pps.c33
1 files changed, 33 insertions, 0 deletions
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
@@ -352,11 +352,44 @@ 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
*/