From bd4a357b3d27fe4cc292bc915f9d022feb9dc499 Mon Sep 17 00:00:00 2001
From: "Shuowang (Wayne) Zhang" <shuowang.zhang@ibm.com>
Date: Wed, 9 Dec 2020 12:19:26 -0500
Subject: [PATCH] zos: implement uv_get_constrained_memory()

Implementation is based on RLIMIT_MEMLIMIT.

Co-authored-by: Igor Todorovski <itodorov@ca.ibm.com>
PR-URL: https://github.com/libuv/libuv/pull/3133
Reviewed-By: Richard Lau <rlau@redhat.com>
---
 docs/src/misc.rst | 2 +-
 src/unix/os390.c  | 9 ++++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/docs/src/misc.rst b/docs/src/misc.rst
index b2725c39..9a8595e5 100644
--- a/docs/src/misc.rst
+++ b/docs/src/misc.rst
@@ -533,7 +533,7 @@ API
 
     .. note::
         This function currently only returns a non-zero value on Linux, based
-        on cgroups if it is present.
+        on cgroups if it is present, and on z/OS based on RLIMIT_MEMLIMIT.
 
     .. versionadded:: 1.29.0
 
diff --git a/src/unix/os390.c b/src/unix/os390.c
index 2912579a..9f0c8a46 100644
--- a/src/unix/os390.c
+++ b/src/unix/os390.c
@@ -28,6 +28,7 @@
 #include <builtins.h>
 #include <termios.h>
 #include <sys/msg.h>
+#include <sys/resource.h>
 #include "zos-base.h"
 #if defined(__clang__)
 #include "csrsic.h"
@@ -199,7 +200,13 @@ uint64_t uv_get_total_memory(void) {
 
 
 uint64_t uv_get_constrained_memory(void) {
-  return 0;  /* Memory constraints are unknown. */
+  struct rlimit rl;
+
+  /* RLIMIT_MEMLIMIT return value is in megabytes rather than bytes. */
+  if (getrlimit(RLIMIT_MEMLIMIT, &rl) == 0)
+    return rl.rlim_cur * 1024 * 1024;
+
+  return 0; /* There is no memory limit set. */
 }