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@xxxxxxxxxxx>
---
drivers/pps/pps.c | 35 +++++++++++++++++++++++++++++++++++
include/linux/pps_kernel.h | 17 ++++++++++++++---
2 files changed, 49 insertions(+), 3 deletions(-)
diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 2420d5a..9a87565 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -357,6 +357,41 @@ void pps_unregister_cdev(struct pps_device *pps)
}
/*
+ * 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.
+ *
+ * A very important usage note is that the list used is the same as the
+ * list of assigned minor numbers. Thus, a pps device can be looked up
+ * after pps_unregister_source time if there are open file handles preventing
+ * it from being deallocated.
+ *
+ * To ensure that this does not lead to duplicate cookies (which Would
+ * Be Bad), also set the cookie to NULL before unregistering.
+ */
+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
*/
diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h
index 0cc45ae..7db3eb9 100644
--- a/include/linux/pps_kernel.h
+++ b/include/linux/pps_kernel.h
@@ -43,7 +43,7 @@ struct pps_source_info {
int event, void *data); /* PPS echo function */
struct module *owner;
- struct device *dev;
+ struct device *dev; /* Parent device for device_create */
};
struct pps_event_time {
@@ -69,6 +69,7 @@ struct pps_device {
wait_queue_head_t queue; /* PPS event queue */
unsigned int id; /* PPS source unique ID */
+ void const *lookup_cookie; /* pps_lookup_dev only */
struct cdev cdev;
struct device *dev;
struct fasync_struct *async_queue; /* fasync method */
@@ -82,16 +83,26 @@ struct pps_device {
extern struct device_attribute pps_attrs[];
/*
+ * Internal functions.
+ *
+ * These are not actually part of the exported API, but this is a
+ * convenient header file to put them in.
+ */
+
+extern int pps_register_cdev(struct pps_device *pps);
+extern void pps_unregister_cdev(struct pps_device *pps);
+
+/*
* Exported functions
*/
extern struct pps_device *pps_register_source(
struct pps_source_info *info, int default_params);
extern void pps_unregister_source(struct pps_device *pps);
-extern int pps_register_cdev(struct pps_device *pps);
-extern void pps_unregister_cdev(struct pps_device *pps);
extern void pps_event(struct pps_device *pps,
struct pps_event_time *ts, int event, void *data);
+/* Look up a pps device by magic cookie */
+struct pps_device *pps_lookup_dev(void const *cookie);
static inline void timespec_to_pps_ktime(struct pps_ktime *kt,
struct timespec ts)
--
1.8.1.2
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