linux-kernel - Re: [PATCH v8 18/25] powerpc: Implement nvram sync ioctl

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Date:   Mon, 31 Dec 2018 13:16:19 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v8 18/25] powerpc: Implement nvram sync ioctl

On Sun, Dec 30, 2018 at 8:25 AM Finn Thain <fthain@...egraphics.com.au> wrote:
>
> On Sat, 29 Dec 2018, Arnd Bergmann wrote:
>
> > > --- a/drivers/char/nvram.c
> > > +++ b/drivers/char/nvram.c
> > > @@ -48,6 +48,10 @@
> > >  #include <linux/mutex.h>
> > >  #include <linux/pagemap.h>
> > >
> > > +#ifdef CONFIG_PPC
> > > +#include <asm/nvram.h>
> > > +#include <asm/machdep.h>
> > > +#endif
> > >
> > >  static DEFINE_MUTEX(nvram_mutex);
> > >  static DEFINE_SPINLOCK(nvram_state_lock);
> > > @@ -331,6 +335,37 @@ static long nvram_misc_ioctl(struct file *file, unsigned int cmd,
> > >         long ret = -ENOTTY;
> > >
> > >         switch (cmd) {
> > > +#ifdef CONFIG_PPC
> > > +       case OBSOLETE_PMAC_NVRAM_GET_OFFSET:
> > > +               pr_warn("nvram: Using obsolete PMAC_NVRAM_GET_OFFSET ioctl\n");
> > > +               /* fall through */
> > > +       case IOC_NVRAM_GET_OFFSET:
> > > +               ret = -EINVAL;
> > > +#ifdef CONFIG_PPC_PMAC
> >
> > I think it would make be nicer here to keep the ppc bits in arch/ppc,
> > and instead add a .ioctl() callback to nvram_ops.
> >
>
> The problem with having an nvram_ops.ioctl() method is the code in the
> !PPC branch. That code would get duplicated because it's needed by both
> X86 and M68K, to implement the checksum ioctls.

I was thinking you'd just have a common ioctl function that falls
back to the .ioctl callback for any unhandled commands like

    switch (cmd) {
    case NVRAM_INIT:
         ...
         break;
    case ...:
         break;
    default:
         if (ops->ioctl)
                 return ops->ioctl(...);
         return -EINVAL;
    }

Would that work?

       Arnd