v4.19.13 snapshot.
diff --git a/arch/um/kernel/sigio.c b/arch/um/kernel/sigio.c
new file mode 100644
index 0000000..b5e0cbb
--- /dev/null
+++ b/arch/um/kernel/sigio.c
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ * Licensed under the GPL
+ */
+
+#include <linux/interrupt.h>
+#include <irq_kern.h>
+#include <os.h>
+#include <sigio.h>
+
+/* Protected by sigio_lock() called from write_sigio_workaround */
+static int sigio_irq_fd = -1;
+
+static irqreturn_t sigio_interrupt(int irq, void *data)
+{
+ char c;
+
+ os_read_file(sigio_irq_fd, &c, sizeof(c));
+ reactivate_fd(sigio_irq_fd, SIGIO_WRITE_IRQ);
+ return IRQ_HANDLED;
+}
+
+int write_sigio_irq(int fd)
+{
+ int err;
+
+ err = um_request_irq(SIGIO_WRITE_IRQ, fd, IRQ_READ, sigio_interrupt,
+ 0, "write sigio", NULL);
+ if (err) {
+ printk(KERN_ERR "write_sigio_irq : um_request_irq failed, "
+ "err = %d\n", err);
+ return -1;
+ }
+ sigio_irq_fd = fd;
+ return 0;
+}
+
+/* These are called from os-Linux/sigio.c to protect its pollfds arrays. */
+static DEFINE_SPINLOCK(sigio_spinlock);
+
+void sigio_lock(void)
+{
+ spin_lock(&sigio_spinlock);
+}
+
+void sigio_unlock(void)
+{
+ spin_unlock(&sigio_spinlock);
+}