2020-11-23 18:05:11

by Jani Nikula

Subject: [PATCH 3/9] 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.

Suggested-by: Christoph Hellwig <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Signed-off-by: Jani Nikula <[email protected]>
---
include/linux/relay.h | 6 ++++++
kernel/relay.c | 26 +-------------------------
2 files changed, 7 insertions(+), 25 deletions(-)

diff --git a/include/linux/relay.h b/include/linux/relay.h
index b3c4f49f6951..99d024475ba5 100644
--- 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
index d9b8185161a8..dd4ec4ec07f3 100644
--- 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);
--
2.20.1

2020-11-24 09:42:07

by Christoph Hellwig

Subject: Re: [PATCH 3/9] relay: make create_buf_file and remove_buf_file callbacks mandatory

On Mon, Nov 23, 2020 at 07:59:23PM +0200, Jani Nikula wrote:
> 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.

Looks good,

Reviewed-by: Christoph Hellwig <[email protected]>