linux-kernel - Re: [PATCH] vfio: Use filp instead of fd

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Message-ID: <YzH/qXr6bZaTY+EV@ZenIV>
Date:   Mon, 26 Sep 2022 20:38:17 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Deming Wang <wangdeming@...pur.com>, pbonzini@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio: Use filp instead of fd

On Mon, Sep 26, 2022 at 02:07:43PM -0300, Jason Gunthorpe wrote:
> On Mon, Sep 26, 2022 at 02:54:07AM -0400, Deming Wang wrote:
> > The function of kvm_vfio_group_set_spapr_tce and kvm_vfio_group_del
> > use fd indirectly.But,it only be used for fd.file. So,we can directly
> > use the struct of file instead.
> > 
> > Signed-off-by: Deming Wang <wangdeming@...pur.com>
> > ---
> >  virt/kvm/vfio.c | 24 ++++++++++++------------
> >  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> I thought about changing this too when I was looking at
> this. fdget/fdput includes a tiny micro-optimization that is legal
> here, however I doubt anyone cares about performance on this path.

Microoptimization or not, I'd rather keep fget() limited to cases where
we really need it.  There are non-trivial cases and having them easy
to find is a good thing.

Again, the preferred way to do descriptor lookups is fdget() family,
not fget() one.