SSL: SSL_sendfile() support with kernel TLS. Requires OpenSSL 3.0 compiled with "enable-ktls" option. Further, KTLS needs to be enabled in kernel, and in OpenSSL, either via OpenSSL configuration file or with "ssl_conf_command Options KTLS;" in nginx configuration. On FreeBSD, kernel TLS is available starting with FreeBSD 13.0, and can be enabled with "sysctl kern.ipc.tls.enable=1" and "kldload ktls_ocf" to load a software backend, see man ktls(4) for details. On Linux, kernel TLS is available starting with kernel 4.13 (at least 5.2 is recommended), and needs kernel compiled with CONFIG_TLS=y (with CONFIG_TLS=m, which is used at least on Ubuntu 21.04 by default, the tls module needs to be loaded with "modprobe tls").

--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -1683,9 +1683,6 @@ ngx_http_upstream_ssl_init_connection(ng
         return;
     }
 
-    c->sendfile = 0;
-    u->output.sendfile = 0;
-
     if (u->conf->ssl_server_name || u->conf->ssl_verify) {
         if (ngx_http_upstream_ssl_name(r, u, c) != NGX_OK) {
             ngx_http_upstream_finalize_request(r, u,
@@ -1791,6 +1788,11 @@ ngx_http_upstream_ssl_handshake(ngx_http
             }
         }
 
+        if (!c->ssl->sendfile) {
+            c->sendfile = 0;
+            u->output.sendfile = 0;
+        }
+
         c->write->handler = ngx_http_upstream_handler;
         c->read->handler = ngx_http_upstream_handler;