[PATCH libinput 1/2] util: introduce ratelimit helpers

David Herrmann dh.herrmann at gmail.com
Wed Nov 5 03:30:32 PST 2014


Hi

On Wed, Nov 5, 2014 at 6:11 AM, Peter Hutterer <peter.hutterer at who-t.net> wrote:
> On Tue, Nov 04, 2014 at 09:35:37AM +0100, David Herrmann wrote:
>> This adds "struct ratelimit" and "ratelimit_test()". It's a very simple
>> rate-limit helper modeled after Linux' lib/ratelimit.c by Dave Young.
>>
>> This comes in handy to limit log-messages in possible busy loops etc..
>>
>> Signed-off-by: David Herrmann <dh.herrmann at gmail.com>
>> ---
>>  src/libinput-util.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  src/libinput-util.h | 19 +++++++++++++++++++
>>  test/misc.c         | 37 +++++++++++++++++++++++++++++++++++++
>>  3 files changed, 104 insertions(+)
>>
>> diff --git a/src/libinput-util.c b/src/libinput-util.c
>> index eeb9786..19594e3 100644
>> --- a/src/libinput-util.c
>> +++ b/src/libinput-util.c
>> @@ -65,3 +65,51 @@ list_empty(const struct list *list)
>>  {
>>       return list->next == list;
>>  }
>> +
>> +/*
>> + * Perform rate-limit test. Returns true if the rate-limited action is still
>> + * allowed, false if it should be suppressed.
>> + *
>> + * The ratelimit object must be initialized via RATELIMIT_INIT().
>> + *
>> + * Modelled after Linux' lib/ratelimit.c by Dave Young
>> + * <hidave.darkstar at gmail.com>, which is licensed GPLv2.
>> + */
>> +bool ratelimit_test(struct ratelimit *r)
>
> libinput style is: return type on a separate line

Fixed.

>> +{
>> +     struct timespec ts;
>> +     uint64_t utime;
>> +
>> +     if (r->interval <= 0 || r->burst <= 0)
>> +             return true;
>> +
>> +     clock_gettime(CLOCK_MONOTONIC, &ts);
>> +     utime = ts.tv_sec * 1000 * 1000 + ts.tv_nsec / 1000;
>> +
>> +     if (r->begin <= 0 || r->begin + r->interval < utime) {
>> +             /* reset counter */
>> +             r->begin = utime;
>> +             r->num = 1;
>> +             return true;
>> +     } else if (r->num < r->burst) {
>> +             /* continue burst */
>> +             r->num++;
>> +             return true;
>> +     }
>> +
>> +     /* rate-limit with overflow check */
>> +     if (r->num + 1 > r->num)
>> +             ++r->num;
>> +
>> +     return false;
>> +}
>> +
>> +/*
>> + * Return true if the ratelimit counter just crossed the cutoff value. That is,
>> + * this function returns true iff the last call to ratelimit_test() was the
>
> s/iff/if/

"Iff" is widely used for "if, and only if," [1]. Should I still change it?

>> + * first call to exceed the burst value in this interval.
>> + */
>> +bool ratelimit_cutoff(struct ratelimit *r)
>
> bool on separate line please

Fixed.

>> +{
>> +     return r->num == r->burst + 1;
>> +}
>
>
> I'm wondering: why have two separate functions here?
>
> how about an
> enum ratelimit {
>         RATELIMIT_PASS,
>         RATELIMIT_THRESHOLD,
>         RATELIMIT_EXCEEDED,
> };
>
> then return that from ratelimit_test and then use the return value to
> decide on the rest of the handling?
> so the dispatch code would be:
> if ((rc = ratelimit_test(...)) != RATELIMIT_EXCEEDED)) {
>      log_info("SYN_DROPPED....");
>      if (rc == RATELIMIT_THRESHOLD) {
>         log_info("SYN_DROPPED flood");
>      }
> }
>
> or the same with a switch statement.

Sure, can do that.

>> diff --git a/src/libinput-util.h b/src/libinput-util.h
>> index 51759e8..8ff8778 100644
>> --- a/src/libinput-util.h
>> +++ b/src/libinput-util.h
>> @@ -25,6 +25,7 @@
>>
>>  #include <unistd.h>
>>  #include <math.h>
>> +#include <stdbool.h>
>>  #include <string.h>
>>  #include <time.h>
>>
>> @@ -280,4 +281,22 @@ matrix_to_farray6(const struct matrix *m, float out[6])
>>       out[5] = m->val[1][2];
>>  }
>>
>> +struct ratelimit {
>> +     uint64_t interval;
>> +     uint64_t begin;
>> +     unsigned burst;
>> +     unsigned num;
>
> unsigned int please

Fixed.

>> +} RateLimit;
>
> well, hello. what are you doing here? are you lost? :)

Weird.. gcc didn't warn me about this unused variable.. Fixed.

>> +
>> +#define RATELIMIT_INIT(_interval, _burst)            \
>> +     ((struct ratelimit){                            \
>> +             .interval = (_interval),                \
>> +             .begin = 0,                             \
>> +             .burst = (_burst),                      \
>> +             .num = 0,                               \
>> +     })
>
> any reason you didn't make this into a function of
> void ratelimit_init(struct ratelimit *rl)?
> I don't see a lot of benefits having this as a macro given that it's only
> called once anyway (per context).

If you want it as global variable, you cannot use a function to
initialize it. I usually prefer literals to initialize objects as it
can be optimized by the compiler. But I can provide ratelimit_init(),
if you want. For the single use-case we have, both are fine.

>> +
>> +bool ratelimit_test(struct ratelimit *r);
>> +bool ratelimit_cutoff(struct ratelimit *r);
>> +
>>  #endif /* LIBINPUT_UTIL_H */
>> diff --git a/test/misc.c b/test/misc.c
>> index 1512180..70b3e57 100644
>> --- a/test/misc.c
>> +++ b/test/misc.c
>> @@ -508,6 +508,42 @@ START_TEST(matrix_helpers)
>>  }
>>  END_TEST
>>
>> +START_TEST(ratelimit_helpers)
>> +{
>> +     /* 10 attempts every 10ms */
>> +     struct ratelimit rl = RATELIMIT_INIT(10000, 10);
>> +     unsigned int i, j;
>> +
>> +     for (j = 0; j < 100; ++j) {
>> +             /* a burst of 10 attempts must succeed */
>> +             for (i = 0; i < 10; ++i) {
>> +                     ck_assert(ratelimit_test(&rl));
>> +                     ck_assert(!ratelimit_cutoff(&rl));
>> +             }
>> +
>> +             /* ..then further attempts must fail.. */
>> +             ck_assert(!ratelimit_test(&rl));
>> +             ck_assert(ratelimit_cutoff(&rl));
>
> you could just drop the above two lines and merge the comments into one.

Ugh? I cannot drop them, as the _cutoff() is only true here, not in
the loop below.

>> +
>> +             /* ..regardless of how often we try. */
>> +             for (i = 0; i < 100; ++i) {
>> +                     ck_assert(!ratelimit_test(&rl));
>> +                     ck_assert(!ratelimit_cutoff(&rl));
>> +             }
>> +
>> +             /* ..even after waiting 5ms */
>> +             usleep(5000);
>
> msleep(5) for consistency with the rest of the code please.

Sure, fixed!

>> +             for (i = 0; i < 100; ++i) {
>> +                     ck_assert(!ratelimit_test(&rl));
>> +                     ck_assert(!ratelimit_cutoff(&rl));
>> +             }
>> +
>> +             /* but after 10ms the counter is reset */
>> +             usleep(6000); /* +1ms to account for time drifts */
>
> same here

Fixed.

>> +     }
>> +}
>> +END_TEST
>> +
>>  int main (int argc, char **argv) {
>>       litest_add_no_device("events:conversion", event_conversion_device_notify);
>>       litest_add_no_device("events:conversion", event_conversion_pointer);
>> @@ -519,5 +555,6 @@ int main (int argc, char **argv) {
>>       litest_add_no_device("config:status string", config_status_string);
>>
>>       litest_add_no_device("misc:matrix", matrix_helpers);
>> +     litest_add_no_device("misc:ratelimit", ratelimit_helpers);
>
> while you're at it, please add an empty line before the return here.

Fixed.

Thanks
David

[1] http://en.wikipedia.org/wiki/If_and_only_if

>>       return litest_run(argc, argv);
>>  }
>> --
>> 2.1.3
>>


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