linux-kernel - Re: [PATCH] mm: add prototype for __add_to_page_cache

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Date:   Tue, 22 Dec 2020 20:40:00 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Alex Shi <alex.shi@...ux.alibaba.com>
Subject: Re: [PATCH] mm: add prototype for __add_to_page_cache_locked()

On Tue, Dec 22, 2020 at 07:49:52PM +0530, Souptick Joarder wrote:
> Otherwise it cause gcc warning:
>           ^~~~~~~~~~~~~~~

That line is just confusing.

> ../mm/filemap.c:830:14: warning: no previous prototype for
> ‘__add_to_page_cache_locked’ [-Wmissing-prototypes]
>  noinline int __add_to_page_cache_locked(struct page *page,
>               ^~~~~~~~~~~~~~~~~~~~~~~~~~

And I don't think those two lines add much value, do you?

> A previous attempt to make this function static leads to
> compile error for few architectures.

It might be better to say why it has to be non-static here (because it's
an error injection point).  And it's not architecture dependent (afaik),
it's whether error injection is enabled in the config.

> Adding a prototype will silence the warning.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Cc: Alex Shi <alex.shi@...ux.alibaba.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  include/linux/mm.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5299b90a..ac07f65 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -216,6 +216,12 @@ int overcommit_kbytes_handler(struct ctl_table *, int, void *, size_t *,
>  		loff_t *);
>  int overcommit_policy_handler(struct ctl_table *, int, void *, size_t *,
>  		loff_t *);
> +/*
> + * Any attempt to mark this function as static leads to build failure
> + * for few architectures. Adding a prototype to silence gcc warning.
> + */

We don't need a comment here for this.  The commit log is enough.

> +int __add_to_page_cache_locked(struct page *page, struct address_space *mapping,
> +		pgoff_t offset, gfp_t gfp, void **shadowp);

Please name that 'index', not 'offset'.