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

7 files changed, 38 insertions, 20 deletions

diff --git a/tests/gobject/timeloop-closure.c b/tests/gobject/timeloop-closure.c
index 9de00d32f..c904c2a45 100644
--- a/tests/gobject/timeloop-closure.c
+++ b/tests/gobject/timeloop-closure.c
@@ -23,7 +23,8 @@ io_pipe (GIOChannel **channels)
 
   if (pipe(fds) < 0)
     {
-      fprintf (stderr, "Cannot create pipe %s\n", g_strerror (errno));
+      int errsv = errno;
+      fprintf (stderr, "Cannot create pipe %s\n", g_strerror (errsv));
       exit (1);
     }
 
@@ -134,7 +135,7 @@ input_callback (GIOChannel   *source,
 static void
 create_child (void)
 {
-  int pid;
+  int pid, errsv;
   GIOChannel *in_channels[2];
   GIOChannel *out_channels[2];
   GSource *source;
@@ -143,6 +144,7 @@ create_child (void)
   io_pipe (out_channels);
 
   pid = fork ();
+  errsv = errno;
 
   if (pid > 0)			/* Parent */
     {
@@ -172,7 +174,7 @@ create_child (void)
     }
   else				/* Error */
     {
-      fprintf (stderr, "Cannot fork: %s\n", g_strerror (errno));
+      fprintf (stderr, "Cannot fork: %s\n", g_strerror (errsv));
       exit (1);
     }
 }
diff --git a/tests/mainloop-test.c b/tests/mainloop-test.c
index 5d305508e..9b8386a65 100644
--- a/tests/mainloop-test.c
+++ b/tests/mainloop-test.c
@@ -202,7 +202,8 @@ io_pipe (GIOChannel **channels)
 
   if (pipe(fds) < 0)
     {
-      g_warning ("Cannot create pipe %s\n", g_strerror (errno));
+      int errsv = errno;
+      g_warning ("Cannot create pipe %s\n", g_strerror (errsv));
       exit (1);
     }
 
diff --git a/tests/spawn-test-win32-gui.c b/tests/spawn-test-win32-gui.c
index 45529d011..2798ce6da 100644
--- a/tests/spawn-test-win32-gui.c
+++ b/tests/spawn-test-win32-gui.c
@@ -60,7 +60,8 @@ WinMain (struct HINSTANCE__ *hInstance,
       if (write (outfd, &n, sizeof (n)) == -1 ||
 	  write (outfd, "Hello there", n) == -1)
 	{
-	  sprintf (buf, "spawn-test-win32-gui: Write: %s", strerror (errno));
+	  int errsv = errno;
+	  sprintf (buf, "spawn-test-win32-gui: Write: %s", strerror (errsv));
 	  MessageBox (NULL, buf, lpszCmdLine, MB_ICONERROR|MB_SYSTEMMODAL);
 	  exit (1);
 	}
@@ -81,8 +82,9 @@ WinMain (struct HINSTANCE__ *hInstance,
 
       if ((k = read (infd, buf, n)) != n)
 	{
+	  int errsv = errno;
 	  if (k == -1)
-	    sprintf (buf, "spawn-test-win32-gui: Read: %s", strerror (errno));
+	    sprintf (buf, "spawn-test-win32-gui: Read: %s", strerror (errsv));
 	  else
 	    sprintf (buf, "spawn-test-win32-gui: Got only %d bytes", k);
 	  MessageBox (NULL, buf, lpszCmdLine, MB_ICONERROR|MB_SYSTEMMODAL);
@@ -96,7 +98,8 @@ WinMain (struct HINSTANCE__ *hInstance,
       if (write (outfd, &n, sizeof (n)) == -1 ||
 	  write (outfd, "See ya", n) == -1)
 	{
-	  sprintf (buf, "spawn-test-win32-gui: Write: %s", strerror (errno));
+	  int errsv = errno;
+	  sprintf (buf, "spawn-test-win32-gui: Write: %s", strerror (errsv));
 	  MessageBox (NULL, buf, lpszCmdLine, MB_ICONERROR|MB_SYSTEMMODAL);
 	  exit (1);
 	}
diff --git a/tests/spawn-test.c b/tests/spawn-test.c
index 217cfd941..05cce17f8 100644
--- a/tests/spawn-test.c
+++ b/tests/spawn-test.c
@@ -232,8 +232,9 @@ run_tests (void)
 
       if ((k = read (pipeup[0], &n, sizeof (n))) != sizeof (n))
 	{
+	  int errsv = errno;
 	  if (k == -1)
-	    fprintf (stderr, "Read error: %s\n", g_strerror (errno));
+	    fprintf (stderr, "Read error: %s\n", g_strerror (errsv));
 	  else
 	    fprintf (stderr, "Wanted to read %d bytes, got %d\n",
 		     sizeof (n), k);
@@ -242,8 +243,9 @@ run_tests (void)
 
       if ((k = read (pipeup[0], buf, n)) != n)
 	{
+	  int errsv = errno;
 	  if (k == -1)
-	    fprintf (stderr, "Read error: %s\n", g_strerror (errno));
+	    fprintf (stderr, "Read error: %s\n", g_strerror (errsv));
 	  else
 	    fprintf (stderr, "Wanted to read %d bytes, got %d\n",
 		     n, k);
@@ -254,14 +256,16 @@ run_tests (void)
       if (write (pipedown[1], &n, sizeof (n)) == -1 ||
 	  write (pipedown[1], "Bye then", n) == -1)
 	{
-	  fprintf (stderr, "Write error: %s\n", g_strerror (errno));
+	  int errsv = errno;
+	  fprintf (stderr, "Write error: %s\n", g_strerror (errsv));
 	  exit (1);
 	}
 
       if ((k = read (pipeup[0], &n, sizeof (n))) != sizeof (n))
 	{
+	  int errsv = errno;
 	  if (k == -1)
-	    fprintf (stderr, "Read error: %s\n", g_strerror (errno));
+	    fprintf (stderr, "Read error: %s\n", g_strerror (errsv));
 	  else
 	    fprintf (stderr, "Wanted to read %d bytes, got %d\n",
 		     sizeof (n), k);
@@ -270,8 +274,9 @@ run_tests (void)
 
       if ((k = read (pipeup[0], buf, n)) != n)
 	{
+	  int errsv = errno;
 	  if (k == -1)
-	    fprintf (stderr, "Read error: %s\n", g_strerror (errno));
+	    fprintf (stderr, "Read error: %s\n", g_strerror (errsv));
 	  else
 	    fprintf (stderr, "Wanted to read %d bytes, got %d\n",
 		     n, k);
diff --git a/tests/testglib.c b/tests/testglib.c
index e9f7f36bc..b5a833178 100644
--- a/tests/testglib.c
+++ b/tests/testglib.c
@@ -907,6 +907,7 @@ test_file_functions (void)
   char template[32];
   char *name_used, chars[62];
   gint fd, n;
+  int errsv;
   
   strcpy (template, "foobar");
   fd = g_mkstemp (template);
@@ -919,15 +920,17 @@ test_file_functions (void)
   if (fd == -1)
     g_error ("g_mkstemp didn't work for template %s\n", template);
   n = write (fd, hello, hellolen);
+  errsv = errno;
   if (n == -1)
-    g_error ("write() failed: %s\n", g_strerror (errno));
+    g_error ("write() failed: %s\n", g_strerror (errsv));
   else if (n != hellolen)
     g_error ("write() should have written %d bytes, wrote %d\n", hellolen, n);
 
   lseek (fd, 0, 0);
   n = read (fd, chars, sizeof (chars));
+  errsv = errno;
   if (n == -1)
-    g_error ("read() failed: %s\n", g_strerror (errno));
+    g_error ("read() failed: %s\n", g_strerror (errsv));
   else if (n != hellolen)
     g_error ("read() should have read %d bytes, got %d\n", hellolen, n);
 
diff --git a/tests/timeloop-basic.c b/tests/timeloop-basic.c
index 2c11bc506..7f952263a 100644
--- a/tests/timeloop-basic.c
+++ b/tests/timeloop-basic.c
@@ -25,7 +25,8 @@ my_pipe (int *fds)
 {
   if (pipe(fds) < 0)
     {
-      fprintf (stderr, "Cannot create pipe %s\n", strerror (errno));
+      int errsv = errno;
+      fprintf (stderr, "Cannot create pipe %s\n", strerror (errsv));
       exit (1);
     }
 }
@@ -121,7 +122,7 @@ input_callback (int source, int dest)
 void
 create_child (int pos)
 {
-  int pid;
+  int pid, errsv;
   int in_fds[2];
   int out_fds[2];
   
@@ -129,6 +130,7 @@ create_child (int pos)
   my_pipe (out_fds);
 
   pid = fork ();
+  errsv = errno;
 
   if (pid > 0)			/* Parent */
     {
@@ -150,7 +152,7 @@ create_child (int pos)
     }
   else				/* Error */
     {
-      fprintf (stderr,"Cannot fork: %s\n", strerror (errno));
+      fprintf (stderr,"Cannot fork: %s\n", strerror (errsv));
       exit (1);
     }
 }
diff --git a/tests/timeloop.c b/tests/timeloop.c
index a1f69ef6b..8b5aa3641 100644
--- a/tests/timeloop.c
+++ b/tests/timeloop.c
@@ -22,7 +22,8 @@ io_pipe (GIOChannel **channels)
 
   if (pipe(fds) < 0)
     {
-      fprintf (stderr, "Cannot create pipe %s\n", g_strerror (errno));
+      int errsv = errno;
+      fprintf (stderr, "Cannot create pipe %s\n", g_strerror (errsv));
       exit (1);
     }
 
@@ -136,7 +137,7 @@ input_callback (GIOChannel   *source,
 static void
 create_child (void)
 {
-  int pid;
+  int pid, errsv;
   GIOChannel *in_channels[2];
   GIOChannel *out_channels[2];
   
@@ -144,6 +145,7 @@ create_child (void)
   io_pipe (out_channels);
 
   pid = fork ();
+  errsv = errno;
 
   if (pid > 0)			/* Parent */
     {
@@ -166,7 +168,7 @@ create_child (void)
     }
   else				/* Error */
     {
-      fprintf (stderr, "Cannot fork: %s\n", g_strerror (errno));
+      fprintf (stderr, "Cannot fork: %s\n", g_strerror (errsv));
       exit (1);
     }
 }