v4.19.13 snapshot.
diff --git a/arch/um/os-Linux/irq.c b/arch/um/os-Linux/irq.c
new file mode 100644
index 0000000..3658230
--- /dev/null
+++ b/arch/um/os-Linux/irq.c
@@ -0,0 +1,147 @@
+/*
+ * Copyright (C) 2017 - Cambridge Greys Ltd
+ * Copyright (C) 2011 - 2014 Cisco Systems Inc
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Licensed under the GPL
+ */
+
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/epoll.h>
+#include <signal.h>
+#include <string.h>
+#include <irq_user.h>
+#include <os.h>
+#include <um_malloc.h>
+
+/* Epoll support */
+
+static int epollfd = -1;
+
+#define MAX_EPOLL_EVENTS 64
+
+static struct epoll_event epoll_events[MAX_EPOLL_EVENTS];
+
+/* Helper to return an Epoll data pointer from an epoll event structure.
+ * We need to keep this one on the userspace side to keep includes separate
+ */
+
+void *os_epoll_get_data_pointer(int index)
+{
+ return epoll_events[index].data.ptr;
+}
+
+/* Helper to compare events versus the events in the epoll structure.
+ * Same as above - needs to be on the userspace side
+ */
+
+
+int os_epoll_triggered(int index, int events)
+{
+ return epoll_events[index].events & events;
+}
+/* Helper to set the event mask.
+ * The event mask is opaque to the kernel side, because it does not have
+ * access to the right includes/defines for EPOLL constants.
+ */
+
+int os_event_mask(int irq_type)
+{
+ if (irq_type == IRQ_READ)
+ return EPOLLIN | EPOLLPRI;
+ if (irq_type == IRQ_WRITE)
+ return EPOLLOUT;
+ return 0;
+}
+
+/*
+ * Initial Epoll Setup
+ */
+int os_setup_epoll(void)
+{
+ epollfd = epoll_create(MAX_EPOLL_EVENTS);
+ return epollfd;
+}
+
+/*
+ * Helper to run the actual epoll_wait
+ */
+int os_waiting_for_events_epoll(void)
+{
+ int n, err;
+
+ n = epoll_wait(epollfd,
+ (struct epoll_event *) &epoll_events, MAX_EPOLL_EVENTS, 0);
+ if (n < 0) {
+ err = -errno;
+ if (errno != EINTR)
+ printk(
+ UM_KERN_ERR "os_waiting_for_events:"
+ " epoll returned %d, error = %s\n", n,
+ strerror(errno)
+ );
+ return err;
+ }
+ return n;
+}
+
+
+/*
+ * Helper to add a fd to epoll
+ */
+int os_add_epoll_fd(int events, int fd, void *data)
+{
+ struct epoll_event event;
+ int result;
+
+ event.data.ptr = data;
+ event.events = events | EPOLLET;
+ result = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);
+ if ((result) && (errno == EEXIST))
+ result = os_mod_epoll_fd(events, fd, data);
+ if (result)
+ printk("epollctl add err fd %d, %s\n", fd, strerror(errno));
+ return result;
+}
+
+/*
+ * Helper to mod the fd event mask and/or data backreference
+ */
+int os_mod_epoll_fd(int events, int fd, void *data)
+{
+ struct epoll_event event;
+ int result;
+
+ event.data.ptr = data;
+ event.events = events;
+ result = epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &event);
+ if (result)
+ printk(UM_KERN_ERR
+ "epollctl mod err fd %d, %s\n", fd, strerror(errno));
+ return result;
+}
+
+/*
+ * Helper to delete the epoll fd
+ */
+int os_del_epoll_fd(int fd)
+{
+ struct epoll_event event;
+ int result;
+ /* This is quiet as we use this as IO ON/OFF - so it is often
+ * invoked on a non-existent fd
+ */
+ result = epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &event);
+ return result;
+}
+
+void os_set_ioignore(void)
+{
+ signal(SIGIO, SIG_IGN);
+}
+
+void os_close_epoll_fd(void)
+{
+ /* Needed so we do not leak an fd when rebooting */
+ os_close_file(epollfd);
+}