Introduced strerrordesc_np() support.

The strerrordesc_np() function, introduced in glibc 2.32, provides an
async-signal-safe way to obtain error messages.  This makes it possible
to avoid copying error messages.

auto/unix

@@ -727,17 +727,33 @@ ngx_feature_test="char buf[1]; struct iovec vec[1]; ssize_t n;
 . auto/feature
 
 
-ngx_feature="sys_nerr"
-ngx_feature_name="NGX_SYS_NERR"
-ngx_feature_run=value
-ngx_feature_incs='#include <errno.h>
-                  #include <stdio.h>'
+# strerrordesc_np(), introduced in glibc 2.32
+
+ngx_feature="strerrordesc_np()"
+ngx_feature_name="NGX_HAVE_STRERRORDESC_NP"
+ngx_feature_run=no
+ngx_feature_incs='#include <string.h>'
 ngx_feature_path=
 ngx_feature_libs=
-ngx_feature_test='printf("%d", sys_nerr);'
+ngx_feature_test="char *p; p = strerrordesc_np(0);
+                  if (p == NULL) return 1"
 . auto/feature
 
 
+if [ $ngx_found = no ]; then
+
+    ngx_feature="sys_nerr"
+    ngx_feature_name="NGX_SYS_NERR"
+    ngx_feature_run=value
+    ngx_feature_incs='#include <errno.h>
+                      #include <stdio.h>'
+    ngx_feature_path=
+    ngx_feature_libs=
+    ngx_feature_test='printf("%d", sys_nerr);'
+    . auto/feature
+fi
+
+
 if [ $ngx_found = no ]; then
 
     # Cygiwn defines _sys_nerr

src/os/unix/ngx_errno.c

@@ -9,6 +9,49 @@
 #include <ngx_core.h>
 
 
+static ngx_str_t   ngx_unknown_error = ngx_string("Unknown error");
+
+
+#if (NGX_HAVE_STRERRORDESC_NP)
+
+/*
+ * The strerrordesc_np() function, introduced in glibc 2.32, is
+ * async-signal-safe.  This makes it possible to use it directly,
+ * without copying error messages.
+ */
+
+
+u_char *
+ngx_strerror(ngx_err_t err, u_char *errstr, size_t size)
+{
+    size_t       len;
+    const char  *msg;
+
+    msg = strerrordesc_np(err);
+
+    if (msg == NULL) {
+        msg = (char *) ngx_unknown_error.data;
+        len = ngx_unknown_error.len;
+
+    } else {
+        len = ngx_strlen(msg);
+    }
+
+    size = ngx_min(size, len);
+
+    return ngx_cpymem(errstr, msg, size);
+}
+
+
+ngx_int_t
+ngx_strerror_init(void)
+{
+    return NGX_OK;
+}
+
+
+#else
+
 /*
  * The strerror() messages are copied because:
  *
@@ -26,7 +69,6 @@
 
 
 static ngx_str_t  *ngx_sys_errlist;
-static ngx_str_t   ngx_unknown_error = ngx_string("Unknown error");
 static ngx_err_t   ngx_first_error;
 static ngx_err_t   ngx_last_error;
 
@@ -164,3 +206,5 @@ failed:
 
     return NGX_ERROR;
 }
+
+#endif