[66/95] relay: make create_buf_file and remove_buf_file callbacks mandatory

Commit Message

Andrew Morton Dec. 16, 2020, 4:45 a.m. UTC

From: Jani Nikula <[e-mail]>
Subject: 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/880[e-mail]
Signed-off-by: Jani Nikula <[e-mail]>
Suggested-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Kalle Valo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/relay.h |    6 ++++++
 kernel/relay.c        |   26 +-------------------------
 2 files changed, 7 insertions(+), 25 deletions(-)

Patch

--- a/include/linux/relay.h~relay-make-create_buf_file-and-remove_buf_file-callbacks-mandatory
+++ a/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);
 };
--- a/kernel/relay.c~relay-make-create_buf_file-and-remove_buf_file-callbacks-mandatory
+++ a/kernel/relay.c
@@ -271,26 +271,6 @@  static int subbuf_start_default_callback
 	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
 {
 	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 *bas
 		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);