[PATCH 5/7] libsupport: remove the LIST_HEAD macro from list.h

["Theodore Ts'o" <tytso@mit.edu>]

The LIST_HEAD macro is defined by both the Linux kernel's list.h and
<sys/queue.h> (originally from BSD).  The problem is that on MacOS,
some system header file pulls in <sys/queue.h> leading to a macro
redefiniction conflict.  Since we don't use LIST_HEAD in e2fsprogs,
the simplest mitigation is to just comment out the definition of LIST_HEAD.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Fixes: 37dafcc0894b ("libsupport: port the kernel list.h to libsupport")
---
 lib/support/list.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/support/list.h b/lib/support/list.h
index 0e00e446d..0ec8de525 100644
--- a/lib/support/list.h
+++ b/lib/support/list.h
@@ -36,8 +36,17 @@ static inline void list_head_destroy(struct list_head *list)
 
 #define LIST_HEAD_INIT(name) { &(name), &(name) }
 
+#if 0
+/*
+ * This conflicts with the LIST_HEAD defined in <sys/queue.h>.  We
+ * don't include it in e2fsprogs, but some systems' header files might
+ * pull it in, leading to the macro redefinition conflict.
+ * Fortunately, we also don't need LIST_HEAD in e2fsprogs, so just
+ * drop this convenience macro.
+ */
 #define LIST_HEAD(name) \
 	struct list_head name = LIST_HEAD_INIT(name)
+#endif
 
 /**
  * INIT_LIST_HEAD - Initialize a list_head structure
-- 
2.53.0