On 2020-04-23 01:42, Dan Gora wrote:
> The getentropy() function was introduced into glibc v2.25 and so is
> not available on all supported platforms. Previously, if DPDK was
> compiled (using meson) on a system which has getentropy(), it would
> introduce a dependency on glibc v2.25 which would prevent that binary
> from running on a system with an older glibc. Similarly if DPDK was
> compiled on a system which did not have getentropy(), getentropy()
> could not be used even if the execution system supported it.
>
> Introduce a new static function, __rte_getentropy() to emulate the
> glibc getentropy() function by reading from /dev/urandom to remove
> this dependency on the glibc version.
>
> Since __rte_genentropy() should never fail, the rdseed method is
> tried first.
>
> Signed-off-by: Dan Gora <d...@adax.com>
> ---
> lib/librte_eal/common/rte_random.c | 62 ++++++++++++++++++++++++++----
> lib/librte_eal/meson.build | 3 --
> 2 files changed, 54 insertions(+), 11 deletions(-)
>
> diff --git a/lib/librte_eal/common/rte_random.c
> b/lib/librte_eal/common/rte_random.c
> index 2c84c8527..f043adf03 100644
> --- a/lib/librte_eal/common/rte_random.c
> +++ b/lib/librte_eal/common/rte_random.c
> @@ -7,6 +7,7 @@
> #endif
> #include <stdlib.h>
> #include <unistd.h>
> +#include <fcntl.h>
>
> #include <rte_branch_prediction.h>
> #include <rte_cycles.h>
> @@ -176,20 +177,61 @@ rte_rand_max(uint64_t upper_bound)
> return res;
> }
>
> +/* Emulate glibc getentropy() using /dev/urandom */
> +static int
> +__rte_getentropy(void *buffer, size_t length)
> +{
> + uint8_t *start = buffer;
> + uint8_t *end;
> + ssize_t bytes;
> + int fd;
> + int rc = -1;
> +
> + if (length > 256) {
> + errno = EIO;
First of all; only the return code is needed, so why bother with errno?
If you would, I suspect it should be rte_errno and not errno (which is
already set).
> + return -1;
> + }
> +
> + fd = open("/dev/urandom", O_RDONLY);
> + if (fd < 0) {
> + errno = ENODEV;
See above.
> + return -1;
> + }
> +
> + end = start + length;
> + while (start < end) {
> + bytes = read(fd, start, end - start);
> + if (bytes < 0) {
> + if (errno == EINTR)
> + /* Supposedly cannot be interrupted by
> + * a signal, but just in case...
> + */
> + continue;
> + else
> + goto out;
> + }
> + if (bytes == 0) {
> + /* no more bytes available, should not happen under
> + * normal circumstances.
> + */
> + errno = EIO;
> + goto out;
> + }
> + start += bytes;
> + }
There's no need for this loop. A /dev/urandom read() is guaranteed to
return as many bytes as requested, up to 256 bytes. See random(4) for
details.
> + rc = 0;
> + errno = 0;
Why are you changing errno? You should never touch errno on success.
> +out:
> + close(fd);
> + return rc;
> +}
> +
> static uint64_t
> __rte_random_initial_seed(void)
> {
> -#ifdef RTE_LIBEAL_USE_GETENTROPY
> - int ge_rc;
> uint64_t ge_seed;
>
> - ge_rc = getentropy(&ge_seed, sizeof(ge_seed));
> -
> - if (ge_rc == 0)
> - return ge_seed;
> -#endif
> #if defined(RTE_ARCH_X86)
> - /* first fallback: rdseed instruction, if available */
> if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_RDSEED)) {
> unsigned int rdseed_low;
> unsigned int rdseed_high;
> @@ -200,6 +242,10 @@ __rte_random_initial_seed(void)
> ((uint64_t)rdseed_high << 32);
> }
> #endif
> + /* first fallback: read from /dev/urandom.. */
Remove "..".
> + if (__rte_getentropy(&ge_seed, sizeof(ge_seed)) == 0)
> + return ge_seed;
> +
> /* second fallback: seed using rdtsc */
> return rte_get_tsc_cycles();
> }
> diff --git a/lib/librte_eal/meson.build b/lib/librte_eal/meson.build
> index 0267c3b9d..748359b8c 100644
> --- a/lib/librte_eal/meson.build
> +++ b/lib/librte_eal/meson.build
> @@ -15,9 +15,6 @@ deps += 'kvargs'
> if dpdk_conf.has('RTE_USE_LIBBSD')
> ext_deps += libbsd
> endif
> -if cc.has_function('getentropy', prefix : '#include <unistd.h>')
> - cflags += '-DRTE_LIBEAL_USE_GETENTROPY'
> -endif
> if cc.has_header('getopt.h')
> cflags += ['-DHAVE_GETOPT_H', '-DHAVE_GETOPT', '-DHAVE_GETOPT_LONG']
> endif
