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author | George Spelvin <linux@horizon.com> | 2013-02-10 04:08:32 -0500 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-02-13 09:40:35 -0800 |
commit | 513b032c98b4b9414aa4e9b4a315cb1bf0380101 (patch) | |
tree | 3483659abdcc63cb831bf9ded62e981de3ffd5e3 /drivers/pps | |
parent | 6d53c3b71d32da665dc2742c1e8663741f27d3cd (diff) | |
download | linux-3.10-513b032c98b4b9414aa4e9b4a315cb1bf0380101.tar.gz linux-3.10-513b032c98b4b9414aa4e9b4a315cb1bf0380101.tar.bz2 linux-3.10-513b032c98b4b9414aa4e9b4a315cb1bf0380101.zip |
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/pps')
-rw-r--r-- | drivers/pps/pps.c | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c index 2420d5af058..a70e384262e 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 */ |