mwifiex_get_random_ba_threshold() uses a complex homegrown implementation
to generate a pseudo-random number from the current time as returned
from do_gettimeofday().
This currently requires two 32-bit divisions plus a couple of other
computations that are eventually discarded as only eight bits of
the microsecond portion are used at all.
We could replace this with a call to get_random_bytes(), but that
might drain the entropy pool too fast if this is called for each
packet.
Instead, this patch converts it to use ktime_get_ns(), which is a
bit faster than do_gettimeofday(), and then uses a similar algorithm
as before, but in a way that takes both the nanosecond and second
portion into account for slightly-more-but-still-not-very-random
pseudorandom number.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Amitkumar Karwar <akarwar@xxxxxxxxxxx>
Cc: Nishant Sarmukadam <nishants@xxxxxxxxxxx>
Cc: Kalle Valo <kvalo@xxxxxxxxxxxxxx>
Cc: linux-wireless@xxxxxxxxxxxxxxx
---
drivers/net/wireless/mwifiex/wmm.c | 15 ++++-----------
1 file changed, 4 insertions(+), 11 deletions(-)
diff --git a/drivers/net/wireless/mwifiex/wmm.c b/drivers/net/wireless/mwifiex/wmm.c
index 173d3663c2e0..878d358063dc 100644
--- a/drivers/net/wireless/mwifiex/wmm.c
+++ b/drivers/net/wireless/mwifiex/wmm.c
@@ -117,22 +117,15 @@ mwifiex_wmm_allocate_ralist_node(struct mwifiex_adapter *adapter, const u8 *ra)
*/
static u8 mwifiex_get_random_ba_threshold(void)
{
- u32 sec, usec;
- struct timeval ba_tstamp;
- u8 ba_threshold;
-
+ u64 ns;
/* setup ba_packet_threshold here random number between
* [BA_SETUP_PACKET_OFFSET,
* BA_SETUP_PACKET_OFFSET+BA_SETUP_MAX_PACKET_THRESHOLD-1]
*/
+ ns = ktime_get_ns();
+ ns += (ns >> 32) + (ns >> 16);
- do_gettimeofday(&ba_tstamp);
- sec = (ba_tstamp.tv_sec & 0xFFFF) + (ba_tstamp.tv_sec >> 16);
- usec = (ba_tstamp.tv_usec & 0xFFFF) + (ba_tstamp.tv_usec >> 16);
- ba_threshold = (((sec << 16) + usec) % BA_SETUP_MAX_PACKET_THRESHOLD)
- + BA_SETUP_PACKET_OFFSET;
-
- return ba_threshold;
+ return ((u8)ns % BA_SETUP_MAX_PACKET_THRESHOLD) + BA_SETUP_PACKET_OFFSET;
}
/*
--
2.1.0.rc2
--
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