introduce FMODE_OPENED

basically, "is that instance set up enough for regular fput(), or
do we want put_filp() for that one".

NOTE: the only alloc_file() caller that could be followed by put_filp()
is in arch/ia64/kernel/perfmon.c, which is (Kconfig-level) broken.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/open.c b/fs/open.c
index 4c65ede..f3c6cb6a 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -749,7 +749,7 @@
 	f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
 
 	if (unlikely(f->f_flags & O_PATH)) {
-		f->f_mode = FMODE_PATH;
+		f->f_mode = FMODE_PATH | FMODE_OPENED;
 		f->f_op = &empty_fops;
 		return 0;
 	}
@@ -793,6 +793,7 @@
 		if (error)
 			goto cleanup_all;
 	}
+	f->f_mode |= FMODE_OPENED;
 	if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 		i_readcount_inc(inode);
 	if ((f->f_mode & FMODE_READ) &&