Re: [PATCH 1/2] NFSD: Fix duplicate fsnotify access events for iterator READs

[Christoph Hellwig <hch@infradead.org>]

On Sat, Aug 22, 2026 at 12:21:12PM +0200, Amir Goldstein wrote:
> (1) In this series
> https://lore.kernel.org/linux-fsdevel/20231122122715.2561213-1-amir73il@gmail.com/
> we intentionally moved the permission hook outside
> of the splice iterators because we wanted to avoid calling them
> with freeze protection held and also there were some duplicate calls
> for this work.

This got me into a little rathole of looking into the other
do_splice_direct_actor callers.  And I still don't understand why
taking file_start_write outside the main splice machinery is fine
for splice_file_range callers, but not for do_splice_direct callers,
and what consideration exists for potential new callers.
(and yes, the naming does not help)

> (2) emitting many READ events from an iterator instead of one event for
> the user's READ request is more noisy and serves no purpose to users.
> In most cases (but not always) those events could be merged, but at the
> cost of futile CPU cycles.

Yes.

> >From a quick inspection of the code, it looks like:
> - fsnotify_access() is missing in vfs_splice_read()

Yes.  Then again I don't really understand vfs_splice_read, it basically
just forward ->splice_read.  I guess for backing_file this is
expected and matches what do_backing_file_read_iter does. for
code it looks weird as the context doesn't change at all.

> - the naming convention for splice_ do_splice_ vfs_splice_ is a horror

The entire cascade of do_*, *actor* and the whole structure of the
splіce code is horrible unfortunately.  Part of that is due to the
mess of inflicting a fake pipe for the fastpath callers that don't
need it, but paet of it is just self-inflicted bad naming.

> - we could make the low level splice_direct_to_actor() static and possibly
>   rename it to splice_direct_to_actor_sd() or something
> - we could export vfs_splice_direct_to_actor() for nfsd which wraps
>   splice_direct_to_actor() with permission hook and fsnotify_access

The latter is the right thing to do.