relay: make create_buf_file and remove_buf_file callbacks mandatory

All clients provide create_buf_file and remove_buf_file callbacks, and they're required for relay to make sense. There is no point in them being optional. Also document whether each callback is mandatory/optional. Link: https://lkml.kernel.org/r/88003c1527386b93036e286e7917f1e33aec84ac.1606153547.git.jani.nikula@intel.com Signed-off-by: Jani Nikula <[email protected]> Suggested-by: Christoph Hellwig <[email protected]> Reviewed-by: Christoph Hellwig <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Kalle Valo <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
berg · Dec 16, 2020 · 371e038 · 371e038
1 parent 6f8f254
commit 371e038
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Showing 2 changed files with 7 additions and 25 deletions.
diff --git a/include/linux/relay.h b/include/linux/relay.h
@@ -89,6 +89,8 @@ struct rchan_callbacks
 	 * The client should return 1 to continue logging, 0 to stop
 	 * logging.
 	 *
+	 * This callback is optional.
+	 *
 	 * NOTE: subbuf_start will also be invoked when the buffer is
 	 *       created, so that the first sub-buffer can be initialized
 	 *       if necessary.  In this case, prev_subbuf will be NULL.
@@ -122,6 +124,8 @@ struct rchan_callbacks
 	 * cause relay_open() to create a single global buffer rather
 	 * than the default set of per-cpu buffers.
 	 *
+	 * This callback is mandatory.
+	 *
 	 * See Documentation/filesystems/relay.rst for more info.
 	 */
 	struct dentry *(*create_buf_file)(const char *filename,
@@ -139,6 +143,8 @@ struct rchan_callbacks
 	 * channel buffer.
 	 *
 	 * The callback should return 0 if successful, negative if not.
+	 *
+	 * This callback is mandatory.
 	 */
 	int (*remove_buf_file)(struct dentry *dentry);
 };

diff --git a/kernel/relay.c b/kernel/relay.c
@@ -271,26 +271,6 @@ static int subbuf_start_default_callback (struct rchan_buf *buf,
 	return 1;
 }
 
-/*
- * create_buf_file_create() default callback.  Does nothing.
- */
-static struct dentry *create_buf_file_default_callback(const char *filename,
-						       struct dentry *parent,
-						       umode_t mode,
-						       struct rchan_buf *buf,
-						       int *is_global)
-{
-	return NULL;
-}
-
-/*
- * remove_buf_file() default callback.  Does nothing.
- */
-static int remove_buf_file_default_callback(struct dentry *dentry)
-{
-	return -EINVAL;
-}
-
 /**
  *	wakeup_readers - wake up readers waiting on a channel
  *	@work: contains the channel buffer
@@ -467,10 +447,6 @@ static void setup_callbacks(struct rchan *chan,
 {
 	if (!cb->subbuf_start)
 		cb->subbuf_start = subbuf_start_default_callback;
-	if (!cb->create_buf_file)
-		cb->create_buf_file = create_buf_file_default_callback;
-	if (!cb->remove_buf_file)
-		cb->remove_buf_file = remove_buf_file_default_callback;
 	chan->cb = cb;
 }
 
@@ -530,7 +506,7 @@ struct rchan *relay_open(const char *base_filename,
 		return NULL;
 	if (subbuf_size > UINT_MAX / n_subbufs)
 		return NULL;
-	if (!cb)
+	if (!cb || !cb->create_buf_file || !cb->remove_buf_file)
 		return NULL;
 
 	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);