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Date:   Tue, 16 Aug 2022 17:32:08 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-fsdevel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC][PATCH] Change calling conventions for filldir_t
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On Tue, Aug 16, 2022 at 05:24:16PM +0100, Matthew Wilcox wrote:
> > The former tended to use 0/-E... conventions - -E<something> on failure.
> > The latter tended to use 0/1, 1 being "stop, we are done".
> > The callers treated anything non-zero as "stop", ignoring which
> > non-zero value did they get.
> > 
> > "true means stop" would be more natural for the second group; "true
> > means keep going" - for the first one.  I tried both variants and
> > the things like
> > 	if allocation failed
> > 		something = -ENOMEM;
> > 		return true;
> > just looked unnatural and asking for trouble.
> 
> I like it the way you have it.  My only suggestion is:
> 
> +++ b/include/linux/fs.h
> @@ -2039,6 +2039,7 @@ extern bool may_open_dev(const struct path *path);
>   * the kernel specify what kind of dirent layout it wants to have.
>   * This allows the kernel to read directories into kernel space or
>   * to have different dirent layouts depending on the binary type.
> + * Return 'true' to keep going and 'false' if there are no more entries.
>   */
>  struct dir_context;
>  typedef int (*filldir_t)(struct dir_context *, const char *, int, loff_t, u64,

OK...  FWIW, an additional argument is that ->iterate() instances are
not calling those directly - they are calling dir_emit(), which returns
true for "keep going" and false for "stop".  This makes the calling
conventions for callbacks match that...