Re: [RFC 30/32] /dev/port: don't compile file operations without CONFIG_DEVPORT

Greg Kroah-Hartman
2021-12-29T10:38:17Z

On Wed, Dec 29, 2021 at 11:25:12AM +0100, Niklas Schnelle wrote:
> 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@kernel.org>
> > > Signed-off-by: Arnd Bergmann <arnd@kernel.org>
> > > Signed-off-by: Niklas Schnelle <schnelle@linux.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

Great, feel free to send this individually, not as a RFC patch, and I
will be glad to queue it up.

thanks,

greg k-h