Many performance tests use rte_rand() and the random number can perturb the results. Add an ability to override the automatic random seed on DPDK startup.
This is not a security problem since rte_rand() is documented as not being cryptographically secure. Signed-off-by: Stephen Hemminger <[email protected]> Reviewed-by: Morten Brørup <[email protected]> --- v2 - fix header inclusion - add docbook comment lib/eal/common/rte_random.c | 14 +++++++++++++- lib/eal/include/rte_random.h | 8 +++++--- 2 files changed, 18 insertions(+), 4 deletions(-) diff --git a/lib/eal/common/rte_random.c b/lib/eal/common/rte_random.c index 576a32a46c..3cc0e3ec5f 100644 --- a/lib/eal/common/rte_random.c +++ b/lib/eal/common/rte_random.c @@ -8,6 +8,7 @@ #endif #endif #include <unistd.h> +#include <stdlib.h> #include <rte_bitops.h> #include <rte_branch_prediction.h> @@ -247,7 +248,18 @@ eal_rand_init(void) RTE_LCORE_VAR_ALLOC(rand_state); - seed = __rte_random_initial_seed(); + const char *env = getenv("DPDK_RANDOM_SEED"); + if (env != NULL && *env != '\0') { + char *end; + + errno = 0; + seed = strtoull(env, &end, 0); + if (errno != 0 || *end != '\0') + rte_exit(EXIT_FAILURE, + "invalid DPDK_RANDOM_SEED: %s\n", env); + } else { + seed = __rte_random_initial_seed(); + } rte_srand(seed); } diff --git a/lib/eal/include/rte_random.h b/lib/eal/include/rte_random.h index 15cbe6215a..bdd4001e78 100644 --- a/lib/eal/include/rte_random.h +++ b/lib/eal/include/rte_random.h @@ -20,9 +20,11 @@ extern "C" { /** * Seed the pseudo-random generator. * - * The generator is automatically seeded by the EAL init with a timer - * value. It may need to be re-seeded by the user with a real random - * value. + * The generator is automatically seeded by the EAL init with + * a system provided random entropy source. But for testing + * it can be useful to force a repeatable starting point by + * setting the initial seed. This can be done by setting + * the `DPDK_RANDOM_SEED` environment variable. * * This function is not multi-thread safe in regards to other * rte_srand() calls, nor is it in relation to concurrent rte_rand(), -- 2.53.0
