[PATCH] debugfs: Reduce <linux/debugfs.h> dependencies

The current <linux/debugfs.h> include file is a little fragile in that
it is not self-contained and hence may cause compile warnings or
errors depending on the files included before it, the kernel config
and the architecture.  This patch makes things a little more robust by:

 - including <linux/types.h> to get definitions of u32, mode_t, and so on.
 - forward declaring struct file_operations.
 - including <linux/err.h> when CONFIG_DEBUG_FS is not set

The last change is particularly useful, as a kernel developer is
likely to build with debugfs always enabled and never see the build
breakage cased if debugfs is disabled.

Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/debugfs.h

@@ -17,6 +17,10 @@
 
 #include <linux/fs.h>
 
+#include <linux/types.h>
+
+struct file_operations;
+
 #if defined(CONFIG_DEBUG_FS)
 struct dentry *debugfs_create_file(const char *name, mode_t mode,
 				   struct dentry *parent, void *data,
@@ -36,6 +40,9 @@ struct dentry *debugfs_create_bool(const char *name, mode_t mode,
 				  struct dentry *parent, u32 *value);
 
 #else
+
+#include <linux/err.h>
+
 /* 
  * We do not return NULL from these functions if CONFIG_DEBUG_FS is not enabled
  * so users have a chance to detect if there was a real error or not.  We don't