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

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Date:   Thu, 30 Dec 2021 11:19:05 -0500
From:   Arnd Bergmann <arnd@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        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 Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-riscv <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 Wed, Dec 29, 2021 at 5:38 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> > > > -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.

I think this patch should contain the 'depends on HAS_IOPORT' that
is currently added in a different patch (char: impi, tpm: depend on
HAS_IOPORT).

However, we can't merge that version until HAS_IOPORT is actually
added to the kernel.

      Arnd