linux: fix accept4() ENOSYS detection on i386

accept4() piggybacks on the socketcall() on i386. socketcall() has the flaw that it returns EINVAL instead of ENOSYS when the operation is not supported. The problem is that accept4() also returns EINVAL when its flag argument is invalid. Try to discern between the two failure cases to the best of our abilities.
joyent · Jun 29, 2012 · 27cd5f0 · 27cd5f0
1 parent 4a88b3b
commit 27cd5f0
Showing 1 changed file with 19 additions and 7 deletions.
diff --git a/src/unix/linux/syscalls.c b/src/unix/linux/syscalls.c
@@ -152,13 +152,25 @@
 
 int uv__accept4(int fd, struct sockaddr* addr, socklen_t* addrlen, int flags) {
 #if __i386__
-  unsigned long args[] = {
-    (unsigned long) fd,
-    (unsigned long) addr,
-    (unsigned long) addrlen,
-    (unsigned long) flags
-  };
-  return syscall(__NR_socketcall, 18 /* SYS_ACCEPT4 */, args);
+  unsigned long args[4];
+  int r;
+
+  args[0] = (unsigned long) fd;
+  args[1] = (unsigned long) addr;
+  args[2] = (unsigned long) addrlen;
+  args[3] = (unsigned long) flags;
+
+  r = syscall(__NR_socketcall, 18 /* SYS_ACCEPT4 */, args);
+
+  /* socketcall() raises EINVAL when SYS_ACCEPT4 is not supported but so does
+   * a bad flags argument. Try to distinguish between the two cases.
+   */
+  if (r == -1)
+    if (errno == EINVAL)
+      if ((flags & ~(UV__SOCK_CLOEXEC|UV__SOCK_NONBLOCK)) == 0)
+        errno = ENOSYS;
+
+  return r;
 #elif __NR_accept4
   return syscall(__NR_accept4, fd, addr, addrlen, flags);
 #else