linux-kernel - Re: [RFC 30/32] /dev/port: don't compile file operations without CONFIG

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Date:   Tue, 28 Dec 2021 09:17:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        John Garry <john.garry@...wei.com>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-csky@...r.kernel.org
Subject: Re: [RFC 30/32] /dev/port: don't compile file operations without
 CONFIG_DEVPORT

On Mon, Dec 27, 2021 at 05:43:15PM +0100, Niklas Schnelle wrote:
> In the future inb() and friends will not be available when compiling
> with CONFIG_HAS_IOPORT=n so we must only try to access them here if
> CONFIG_DEVPORT is set which depends on HAS_IOPORT.
> 
> Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> Signed-off-by: Arnd Bergmann <arnd@...nel.org>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
>  drivers/char/mem.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index cc296f0823bd..c1373617153f 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -402,6 +402,7 @@ static int mmap_mem(struct file *file, struct vm_area_struct *vma)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_DEVPORT
>  static ssize_t read_port(struct file *file, char __user *buf,
>  			 size_t count, loff_t *ppos)
>  {
> @@ -443,6 +444,7 @@ static ssize_t write_port(struct file *file, const char __user *buf,
>  	*ppos = i;
>  	return tmp-buf;
>  }
> +#endif
>  
>  static ssize_t read_null(struct file *file, char __user *buf,
>  			 size_t count, loff_t *ppos)
> @@ -665,12 +667,14 @@ static const struct file_operations null_fops = {
>  	.splice_write	= splice_write_null,
>  };
>  
> -static const struct file_operations __maybe_unused port_fops = {
> +#ifdef CONFIG_DEVPORT
> +static const struct file_operations port_fops = {
>  	.llseek		= memory_lseek,
>  	.read		= read_port,
>  	.write		= write_port,
>  	.open		= open_port,
>  };
> +#endif

Why is this #ifdef needed if it is already __maybe_unused?

In looking closer, this change could be taken now as the use of this
variable already is behind this same #ifdef statement, right?

thanks,

greg k-h