linux-kernel - Re: [PATCH v5 03/18] gfs2: add compat

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Date:   Mon, 19 Aug 2019 11:37:57 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andreas Grünbacher <andreas.gruenbacher@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Bob Peterson <rpeterso@...hat.com>,
        Steve Whitehouse <swhiteho@...hat.com>,
        Jan Kara <jack@...e.cz>, NeilBrown <neilb@...e.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        cluster-devel <cluster-devel@...hat.com>
Subject: Re: [PATCH v5 03/18] gfs2: add compat_ioctl support

On Mon, Aug 19, 2019 at 11:09 AM Arnd Bergmann <arnd@...db.de> wrote:
> On Sun, Aug 18, 2019 at 10:17 PM Andreas Grünbacher
> <andreas.gruenbacher@...il.com> wrote:
> > Am So., 18. Aug. 2019 um 21:32 Uhr schrieb Arnd Bergmann <arnd@...db.de>:
> > > On Fri, Aug 16, 2019 at 7:32 PM Andreas Gruenbacher <agruenba@...hat.com> wrote:
> > > > On Wed, Aug 14, 2019 at 10:45 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > > > +       /* These are just misnamed, they actually get/put from/to user an int */
> > > > > +       switch(cmd) {
> > > > > +       case FS_IOC32_GETFLAGS:
> > > > > +               cmd = FS_IOC_GETFLAGS;
> > > > > +               break;
> > > > > +       case FS_IOC32_SETFLAGS:
> > > > > +               cmd = FS_IOC_SETFLAGS;
> > > > > +               break;
> > > >
> > > > I'd like the code to be more explicit here:
> > > >
> > > >         case FITRIM:
> > > >         case FS_IOC_GETFSLABEL:
> > > >               break;
> > > >         default:
> > > >               return -ENOIOCTLCMD;
> > >
> > > I've looked at it again: if we do this, the function actually becomes
> > > longer than the native gfs2_ioctl(). Should we just make a full copy then?
> >
> > I don't think the length of gfs2_compat_ioctl is really an issue as
> > long as the function is that simple.
>
> True. The most important goal should just be to make it easy to
> add the correct handler the next time another command is added
> to the ioctl function.
>
> Just let me know which version you want for that:
>
> 1. my original patch
> 2. the version from your reply

That one, please.

> 3. my version below with compat_ptr() added
> 4. ...
>
> > > static long gfs2_compat_ioctl(struct file *filp, unsigned int cmd,
> > > unsigned long arg)
> > > {
> > >         switch(cmd) {
> > >         case FS_IOC32_GETFLAGS:
> > >                 return gfs2_get_flags(filp, (u32 __user *)arg);
> > >         case FS_IOC32_SETFLAGS:
> > >                 return gfs2_set_flags(filp, (u32 __user *)arg);
> > >         case FITRIM:
> > >                 return gfs2_fitrim(filp, (void __user *)arg);
> > >         case FS_IOC_GETFSLABEL:
> > >                 return gfs2_getlabel(filp, (char __user *)arg);
> > >         }
> > >
> > >         return -ENOTTY;
> > > }
> >
> > Don't we still need the compat_ptr conversion? That seems to be the
> > main point of having a compat_ioctl operation.
>
> Right, of course. Fixed now in my tree.
>
>          Arnd

Thanks,
Andreas