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

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Message-ID: <b9d0c0b88ef66f9beb51a880e765177670a76394.camel@linux.ibm.com>
Date:   Wed, 29 Dec 2021 11:25:12 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 Tue, 2021-12-28 at 09:17 +0100, Greg Kroah-Hartman wrote:
> 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?

Because read_port() calls inb() and write_port() calls outb() they
wouldn't compile once these are no longer defined. Then however the
read_port/write_port symbols in the struct initialization above
couldn't be resolved.

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

Yes

> 
> thanks,
> 
> greg k-h