Add a "fork" of musl as //fusl.

fusl/src/stdio/popen.c

Index: fusl/src/stdio/popen.c
diff --git a/fusl/src/stdio/popen.c b/fusl/src/stdio/popen.c
new file mode 100644
index 0000000000000000000000000000000000000000..92cb57ee937b7ea3908de2c0de86ced5eefb3d8d
--- /dev/null
+++ b/fusl/src/stdio/popen.c
@@ -0,0 +1,73 @@
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <spawn.h>
+#include "stdio_impl.h"
+#include "syscall.h"
+
+extern char **__environ;
+
+FILE *popen(const char *cmd, const char *mode)
+{
+	int p[2], op, e;
+	pid_t pid;
+	FILE *f;
+	posix_spawn_file_actions_t fa;
+
+	if (*mode == 'r') {
+		op = 0;
+	} else if (*mode == 'w') {
+		op = 1;
+	} else {
+		errno = EINVAL;
+		return 0;
+	}
+	
+	if (pipe2(p, O_CLOEXEC)) return NULL;
+	f = fdopen(p[op], mode);
+	if (!f) {
+		__syscall(SYS_close, p[0]);
+		__syscall(SYS_close, p[1]);
+		return NULL;
+	}
+	FLOCK(f);
+
+	/* If the child's end of the pipe happens to already be on the final
+	 * fd number to which it will be assigned (either 0 or 1), it must
+	 * be moved to a different fd. Otherwise, there is no safe way to
+	 * remove the close-on-exec flag in the child without also creating
+	 * a file descriptor leak race condition in the parent. */
+	if (p[1-op] == 1-op) {
+		int tmp = fcntl(1-op, F_DUPFD_CLOEXEC, 0);
+		if (tmp < 0) {
+			e = errno;
+			goto fail;
+		}
+		__syscall(SYS_close, p[1-op]);
+		p[1-op] = tmp;
+	}
+
+	e = ENOMEM;
+	if (!posix_spawn_file_actions_init(&fa)) {
+		if (!posix_spawn_file_actions_adddup2(&fa, p[1-op], 1-op)) {
+			if (!(e = posix_spawn(&pid, "/bin/sh", &fa, 0,
+			    (char *[]){ "sh", "-c", (char *)cmd, 0 }, __environ))) {
+				posix_spawn_file_actions_destroy(&fa);
+				f->pipe_pid = pid;
+				if (!strchr(mode, 'e'))
+					fcntl(p[op], F_SETFD, 0);
+				__syscall(SYS_close, p[1-op]);
+				FUNLOCK(f);
+				return f;
+			}
+		}
+		posix_spawn_file_actions_destroy(&fa);
+	}
+fail:
+	fclose(f);
+	__syscall(SYS_close, p[1-op]);
+
+	errno = e;
+	return 0;
+}