On 7/7/2023 7:21 AM, Anton Khirnov wrote:
It is a better interface for /dev/u?random on Linux, which avoids the
issues associated with opening files.
---
configure | 2 ++
libavutil/random_seed.c | 15 +++++++++++++++
2 files changed, 17 insertions(+)
diff --git a/configure b/configure
index d6e78297fe..a4b09577cf 100755
--- a/configure
+++ b/configure
@@ -2310,6 +2310,7 @@ SYSTEM_FUNCS="
getauxval
getenv
gethrtime
+ getrandom
getopt
GetModuleHandle
GetProcessAffinityMask
@@ -6387,6 +6388,7 @@ check_func fcntl
check_func fork
check_func gethrtime
check_func getopt
+check_func_headers "sys/random.h" getrandom
check_func getrusage
check_func gettimeofday
check_func isatty
diff --git a/libavutil/random_seed.c b/libavutil/random_seed.c
index 2980e565e0..9a3a5aa133 100644
--- a/libavutil/random_seed.c
+++ b/libavutil/random_seed.c
@@ -35,6 +35,9 @@
#elif CONFIG_OPENSSL
#include <openssl/rand.h>
#endif
+#if HAVE_GETRANDOM
+#include <sys/random.h>
+#endif
#include <fcntl.h>
#include <math.h>
#include <time.h>
@@ -51,6 +54,7 @@
#define TEST 0
#endif
+#if !HAVE_GETRANDOM
static int read_random(uint8_t *dst, size_t len, const char *file)
{
#if HAVE_UNISTD_H
@@ -70,6 +74,7 @@ static int read_random(uint8_t *dst, size_t len, const char
*file)
return AVERROR(ENOSYS);
#endif
}
+#endif
static uint32_t get_generic_seed(void)
{
@@ -147,7 +152,17 @@ int av_random_bytes(uint8_t* buf, size_t len)
return 0;
#endif
+ // getrandom() is a better interface for /dev/(u)random on Linux,
+ // so it makes no sense to try both
+#if HAVE_GETRANDOM
+ {
+ ssize_t read = getrandom(buf, len, GRND_NONBLOCK);
+ err = read < 0 ? AVERROR(errno) :
+ read != len ? AVERROR_UNKNOWN : 0;
The documentation states
"By default, when reading from the random source, getrandom() blocks if
no random bytes are available, and when reading from the urandom source,
it blocks if the entropy pool has not yet been initialized.If the
GRND_NONBLOCK flag is set, then getrandom() does not block in these
cases, but instead immediately returns -1 with errno set to EAGAIN."
Returning EAGAIN may end up clashing with our usage of said error value
internally (Marton's patch will make use of this function in hls), so
maybe prevent said value from propagating here.
LGTM otherwise.
+ }
+#else
err = read_random(buf, len, "/dev/urandom");
+#endif
if (!err)
return err;
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