[FFmpeg-devel] [PATCH] lavu/random_seed: use getrandom() when available

[Anton Khirnov]

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 | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/configure b/configure
index 0ab0761011..f8c809e491 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 f167b172f2..92bf9ef8e1 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 +152,18 @@ 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);
+        if (read < 0)
+            return errno == EAGAIN ? AVERROR_EXTERNAL : AVERROR(errno);
+        return read != len ? AVERROR_UNKNOWN : 0;
+    }
+#else
     err = read_random(buf, len, "/dev/urandom");
+#endif
     if (!err)
         return err;
 
-- 
2.40.1