fx.io: add linux support for iostreams and pipes

fx.io/sys/linux/pipe.c

@@ -0,0 +1,29 @@
+#include "posix.h"
+
+#include <errno.h>
+#include <fx/io/stream.h>
+#include <unistd.h>
+
+fx_status fx_pipe_create(fx_iostream **reader, fx_iostream **writer)
+{
+	int fds[2];
+	int err = pipe(fds);
+	if (err != 0) {
+		return fx_status_from_errno(errno, FX_ERR_NOT_SUPPORTED);
+	}
+
+	fx_iostream *r = fx_iostream_create(FX_STREAM_READ, fds[0], true);
+	fx_iostream *w = fx_iostream_create(FX_STREAM_WRITE, fds[1], true);
+
+	if (!r || !w) {
+		fx_iostream_unref(r);
+		fx_iostream_unref(w);
+		close(fds[0]);
+		close(fds[1]);
+		return FX_ERR_NO_MEMORY;
+	}
+
+	*reader = r;
+	*writer = w;
+	return FX_SUCCESS;
+}