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Date: Sun, 28 Jun 2015 21:59:25 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mikulas Patocka <mikulas@twibright.com>, "Ted Ts'o" <tytso@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] hpfs: add fstrim support
Message-ID: <20150628205925.GX17109@ZenIV.linux.org.uk>
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On Sun, Jun 28, 2015 at 12:52:11PM -0700, Linus Torvalds wrote:
> On Sun, Jun 28, 2015 at 6:16 AM, Mikulas Patocka <mikulas@twibright.com> wrote:
> > This patch adds support for fstrim to the HPFS filesystem.
> ...
> > +#ifdef CONFIG_COMPAT
> > +       .compat_ioctl   = hpfs_compat_ioctl,
> > +#endif
> ...
> > +#ifdef CONFIG_COMPAT
> > +       .compat_ioctl   = hpfs_compat_ioctl,
> > +#endif
> ...
> > +#ifdef CONFIG_COMPAT
> > +long hpfs_compat_ioctl(struct file *file, unsigned cmd, unsigned long arg)
> > +{
> > +       return hpfs_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
> > +}
> > +#endif
> 
> Hmm. You've clearly copied this pattern from other filesystems, and so
> I can't really blame you, but this thing annoys me a lot.
> 
> Why isn't FITRIM just marked as a COMPATIBLE_IOCTL(), at which point
> the generic ioctl layer will do exactly the above translation for us?
> 
> Am I missing something?

More to the point, why bother with ->ioctl() at all?  Why not make
->fitrim() a super_block method and let do_vfs_ioctl() handle all
marshalling?  As in
	(int *)fitrim(struct super_block *, struct fstrim_range *);
guaranteed to be called only on a filesystem kept active by caller...