Consistently save errno immediately after the operation setting it

Prevent the situation where errno is set by function A, then function B
is called (which is typically _(), but could be anything else) and it
overwrites errno, then errno is checked by the caller.

errno is a horrific API, and we need to be careful to save its value as
soon as a function call (which might set it) returns. i.e. Follow the
pattern:
  int errsv, ret;
  ret = some_call_which_might_set_errno ();
  errsv = errno;

  if (ret < 0)
    puts (strerror (errsv));

This patch implements that pattern throughout GLib. There might be a few
places in the test code which still use errno directly. They should be
ported as necessary. It doesn’t modify all the call sites like this:
  if (some_call_which_might_set_errno () && errno == ESOMETHING)
since the refactoring involved is probably more harmful than beneficial
there. It does, however, refactor other call sites regardless of whether
they were originally buggy.

https://bugzilla.gnome.org/show_bug.cgi?id=785577

1 files changed, 8 insertions, 3 deletions

diff --git a/gio/gunixfdmessage.c b/gio/gunixfdmessage.c
index 581670328..b80283b0b 100644
--- a/gio/gunixfdmessage.c
+++ b/gio/gunixfdmessage.c
@@ -110,14 +110,19 @@ g_unix_fd_message_deserialize (int      level,
    */
   for (i = 0; i < n; i++)
     {
+      int errsv;
+
       do
-        s = fcntl (fds[i], F_SETFD, FD_CLOEXEC);
-      while (s < 0 && errno == EINTR);
+        {
+          s = fcntl (fds[i], F_SETFD, FD_CLOEXEC);
+          errsv = errno;
+        }
+      while (s < 0 && errsv == EINTR);
 
       if (s < 0)
         {
           g_warning ("Error setting close-on-exec flag on incoming fd: %s",
-                     g_strerror (errno));
+                     g_strerror (errsv));
           return NULL;
         }
     }