linux-kernel - Re: [PATCH] procfs: use inline functions instead of macros for proc_create_single

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Date:   Tue, 29 May 2018 21:20:21 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Rafał Miłecki <rafal@...ecki.pl>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] procfs: use inline functions instead of macros for
 proc_create_single_data stub

On Fri, 25 May 2018 23:45:00 +0200
Arnd Bergmann <arnd@...db.de> wrote:

> The procfs interface changes caused one warning in afs for
> a now unused function:
> 
> fs/afs/proc.c:818:12: error: 'afs_proc_stats_show' defined but not used [-Werror=unused-function]
>  static int afs_proc_stats_show(struct seq_file *m, void *v)
> 
> This can be avoided by using an inline function instead of a macro
> to reference it, so now the compiler can silently drop the function
> after seeing that there is a reference but that it is never called.
> 
> Unfortunately, this change triggers another warning where a function
> is hidden and now unexpectedly referenced:
> 
> drivers/mtd/mtdcore.c: In function 'init_mtd':
> drivers/mtd/mtdcore.c:1878:48: error: 'mtd_proc_show' undeclared (first use in this function); did you mean 'mtd_name_show'?
> 
> It seems nicer to keep using the inline function and removing the #ifdef
> here than to add an #ifdef around every single function we pass into
> proc_create_single_data(), so I'm removing the #ifdef here.
> 
> After a few hundred randconfig builds, this was the only instance
> I found that caused a problem.
> 
> Fixes: 353861cf0594 ("afs: simplify procfs code")
> Fixes: 3f3942aca6da ("proc: introduce proc_create_single{,_data}")
> Cc: Christoph Hellwig <hch@....de>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Boris Brezillon <boris.brezillon@...tlin.com>

> ---
>  drivers/mtd/mtdcore.c   |  3 ---
>  include/linux/proc_fs.h | 10 ++++++++--
>  2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 42395df06be9..08d1e89faf9c 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -1814,8 +1814,6 @@ void *mtd_kmalloc_up_to(const struct mtd_info *mtd, size_t *size)
>  }
>  EXPORT_SYMBOL_GPL(mtd_kmalloc_up_to);
>  
> -#ifdef CONFIG_PROC_FS
> -
>  /*====================================================================*/
>  /* Support for /proc/mtd */
>  
> @@ -1833,7 +1831,6 @@ static int mtd_proc_show(struct seq_file *m, void *v)
>  	mutex_unlock(&mtd_table_mutex);
>  	return 0;
>  }
> -#endif /* CONFIG_PROC_FS */
>  
>  /*====================================================================*/
>  /* Init code */
> diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
> index e518352137e7..3b44c357a6e7 100644
> --- a/include/linux/proc_fs.h
> +++ b/include/linux/proc_fs.h
> @@ -84,8 +84,14 @@ static inline struct proc_dir_entry *proc_mkdir_mode(const char *name,
>  #define proc_create_seq_private(name, mode, parent, ops, size, data) ({NULL;})
>  #define proc_create_seq_data(name, mode, parent, ops, data) ({NULL;})
>  #define proc_create_seq(name, mode, parent, ops) ({NULL;})
> -#define proc_create_single(name, mode, parent, show) ({NULL;})
> -#define proc_create_single_data(name, mode, parent, show, data) ({NULL;})
> +static inline struct proc_dir_entry *proc_create_single_data(const char *name,
> +		umode_t mode, struct proc_dir_entry *parent,
> +		int (*show)(struct seq_file *, void *), void *data)
> +{
> +	return NULL;
> +}
> +#define proc_create_single(name, mode, parent, show) \
> +	proc_create_single_data(name, mode, parent, show, NULL)
>  #define proc_create(name, mode, parent, proc_fops) ({NULL;})
>  #define proc_create_data(name, mode, parent, proc_fops, data) ({NULL;})
>