linux-ext4 - [PATCH v8 23/32] fanotify: Wrap object_fh inline space in a creator macro

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Date:   Mon, 18 Oct 2021 21:00:06 -0300
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     jack@...e.com, amir73il@...il.com
Cc:     djwong@...nel.org, tytso@....edu, david@...morbit.com,
        dhowells@...hat.com, khazhy@...gle.com,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-api@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel@...labora.com, Jan Kara <jack@...e.cz>
Subject: [PATCH v8 23/32] fanotify: Wrap object_fh inline space in a creator macro

fanotify_error_event would duplicate this sequence of declarations that
already exist elsewhere with a slight different size.  Create a helper
macro to avoid code duplication.

Suggested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>

---
Among the suggestions, I think this is simpler because it avoids
deep nesting the variable-sized attribute, which would have been hidden
inside fee->ffe->object_fh.buf.

It also avoids touching the allocators, which are nicely hidden inside
helper KMEM_CACHE() macros that hides several parameters.
---
 fs/notify/fanotify/fanotify.h | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 2b032b79d5b0..a5e81d759f65 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -171,12 +171,19 @@ static inline void fanotify_init_event(struct fanotify_event *event,
 	event->pid = NULL;
 }
 
+#define FANOTIFY_INLINE_FH(size)					\
+struct {								\
+	struct fanotify_fh object_fh;					\
+	/* Space for object_fh.buf[] - access with fanotify_fh_buf() */	\
+	unsigned char _inline_fh_buf[(size)];				\
+}
+
 struct fanotify_fid_event {
 	struct fanotify_event fae;
 	__kernel_fsid_t fsid;
-	struct fanotify_fh object_fh;
-	/* Reserve space in object_fh.buf[] - access with fanotify_fh_buf() */
-	unsigned char _inline_fh_buf[FANOTIFY_INLINE_FH_LEN];
+
+	/* This must be the last element of the structure. */
+	FANOTIFY_INLINE_FH(FANOTIFY_INLINE_FH_LEN);
 };
 
 static inline struct fanotify_fid_event *
-- 
2.33.0