new helper: audit_file()

... for situations when we don't have any candidate in pathnames - basically,
in descriptor-based syscalls.

[Folded the build fix for !CONFIG_AUDITSYSCALL configs from Chen Gang]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ipc/mqueue.c

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 4fcf39a..7635a1c 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -990,7 +990,7 @@
 		goto out_fput;
 	}
 	info = MQUEUE_I(inode);
-	audit_inode(NULL, f.file->f_path.dentry, 0);
+	audit_file(f.file);
 
 	if (unlikely(!(f.file->f_mode & FMODE_WRITE))) {
 		ret = -EBADF;
@@ -1106,7 +1106,7 @@
 		goto out_fput;
 	}
 	info = MQUEUE_I(inode);
-	audit_inode(NULL, f.file->f_path.dentry, 0);
+	audit_file(f.file);
 
 	if (unlikely(!(f.file->f_mode & FMODE_READ))) {
 		ret = -EBADF;