linux-kernel - RE: [virtio-dev] Re: [PATCH v2 1/2] virtio: introduce little edian functions for virtio

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Message-ID: <33183CC9F5247A488A2544077AF19020D97A1087@SZXEMA503-MBS.china.huawei.com>
Date:   Mon, 28 Nov 2016 02:57:06 +0000
From:   "Gonglei (Arei)" <arei.gonglei@...wei.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        Luonengjun <luonengjun@...wei.com>,
        "stefanha@...hat.com" <stefanha@...hat.com>,
        "Huangweidong (C)" <weidong.huang@...wei.com>,
        "Wubin (H)" <wu.wubin@...wei.com>,
        "xin.zeng@...el.com" <xin.zeng@...el.com>,
        Claudio Fontana <Claudio.Fontana@...wei.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "pasic@...ux.vnet.ibm.com" <pasic@...ux.vnet.ibm.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "Zhoujian (jay, Euler)" <jianjay.zhou@...wei.com>,
        "Hanweidong (Randy)" <hanweidong@...wei.com>,
        "arei.gonglei@...mail.com" <arei.gonglei@...mail.com>,
        "cornelia.huck@...ibm.com" <cornelia.huck@...ibm.com>,
        "Xuquan (Quan Xu)" <xuquan8@...wei.com>,
        longpeng <longpeng2@...wei.com>,
        "salvatore.benedetto@...el.com" <salvatore.benedetto@...el.com>
Subject: RE: [virtio-dev] Re: [PATCH v2 1/2] virtio: introduce little edian
 functions for virtio_cread/write# family

>
> Subject: Re: [virtio-dev] Re: [PATCH v2 1/2] virtio: introduce little edian
> functions for virtio_cread/write# family
> 
> On Mon, Nov 28, 2016 at 04:34:56AM +0200, Michael S. Tsirkin wrote:
> > On Mon, Nov 28, 2016 at 01:56:04AM +0000, Gonglei (Arei) wrote:
> > > Hi Michael,
> > >
> > > Thanks for your feedback firstly!
> > >
> > > > -----Original Message-----
> > > > From: virtio-dev@...ts.oasis-open.org
> [mailto:virtio-dev@...ts.oasis-open.org]
> > > > On Behalf Of Michael S. Tsirkin
> > > > Sent: Sunday, November 27, 2016 11:33 AM
> > > > To: Gonglei (Arei)
> > > > Subject: [virtio-dev] Re: [PATCH v2 1/2] virtio: introduce little edian
> functions for
> > > > virtio_cread/write# family
> > > >
> > > > On Tue, Nov 22, 2016 at 04:10:22PM +0800, Gonglei wrote:
> > > > > Virtio modern devices are always little edian, let's introduce
> > > > > the LE functions for read/write configuration space for
> > > > > virtio modern devices, which avoid complaint by Sparse when
> > > > > we use the virtio_creaed/virtio_cwrite in VIRTIO_1 devices.
> > > > >
> > > > > Signed-off-by: Gonglei <arei.gonglei@...wei.com>
> > > > > ---
> > > > >  include/linux/virtio_config.h | 45
> > > > +++++++++++++++++++++++++++++++++++++++++++
> > > > >  1 file changed, 45 insertions(+)
> > > > >
> > > > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > > > > index 26c155b..de05707 100644
> > > > > --- a/include/linux/virtio_config.h
> > > > > +++ b/include/linux/virtio_config.h
> > > > > @@ -414,4 +414,49 @@ static inline void virtio_cwrite64(struct
> virtio_device
> > > > *vdev,
> > > > >  		_r;							\
> > > > >  	})
> > > > >
> > > > > +static inline __le16 virtio_cread16_le(struct virtio_device *vdev,
> > > > > +				 unsigned int offset)
> > > > > +{
> > > > > +	__le16 ret;
> > > > > +
> > > > > +	vdev->config->get(vdev, offset, &ret, sizeof(ret));
> > > > > +	return ret;
> > > > > +}
> > > > > +
> > > > > +static inline void virtio_cwrite16_le(struct virtio_device *vdev,
> > > > > +				   unsigned int offset, __le16 val)
> > > > > +{
> > > > > +	vdev->config->set(vdev, offset, &val, sizeof(val));
> > > > > +}
> > > > > +
> > > > > +static inline __le32 virtio_cread32_le(struct virtio_device *vdev,
> > > > > +				 unsigned int offset)
> > > > > +{
> > > > > +	__le32 ret;
> > > > > +
> > > > > +	vdev->config->get(vdev, offset, &ret, sizeof(ret));
> > > > > +	return ret;
> > > > > +}
> > > > > +
> > > > > +static inline void virtio_cwrite32_le(struct virtio_device *vdev,
> > > > > +				   unsigned int offset, __le32 val)
> > > > > +{
> > > > > +	vdev->config->set(vdev, offset, &val, sizeof(val));
> > > > > +}
> > > > > +
> > > > > +static inline __le64 virtio_cread64_le(struct virtio_device *vdev,
> > > > > +				 unsigned int offset)
> > > > > +{
> > > > > +	__le64 ret;
> > > > > +
> > > > > +	__virtio_cread_many(vdev, offset, &ret, 1, sizeof(ret));
> > > > > +	return ret;
> > > > > +}
> > > > > +
> > > > > +static inline void virtio_cwrite64_le(struct virtio_device *vdev,
> > > > > +				   unsigned int offset, __le64 val)
> > > > > +{
> > > > > +	vdev->config->set(vdev, offset, &val, sizeof(val));
> > > > > +}
> > > > > +
> > > > >  #endif /* _LINUX_VIRTIO_CONFIG_H */
> > > >
> > > > Could you please better explain what is the issue you are facing?
> > > > virtio_cwrite/virtio_cread all accept and return native types.
> > > >
> > > virtio_cwrite/virtio_cread are used to write/read configuration
> > > space for virtio devices. For virtio-crypto device, I used __le32/64 directly
> > > in struct virtio_crypto_config. The sparse reports warnings if I use
> virtio_cread()
> > > for virtio-crypto device.
> >
> > I suspect that's because you are doing cread into an le32 variable.
> >
> >
> >
> > > Furthermore, it means the warnings exist for all VIRTIO_1 devices because
> > > they are definitely LE, which it's not necessary to use
> virtio_to_cpu/cpu_to_virtio.
> > >
> > >
> > > PS: I googled a discussion about this topic for virtio-input device, pls see:
> > >
> http://linux.kernel.narkive.com/3argfbWz/patch-1-1-add-virtio-input-driver
> > >
> > > Regards,
> > > -Gonglei
> >
> > Looks like we changed the macros since - at least ATM
> > virtio_console_config uses __u16 fields (which is probably a bug -
> > I'll look into fixing it up) and they
> > do not seem to trigger warnings.
> 
> 
> Sorry, I recall now. We use u32 and similar types in the config
> space, and endian-ness is implicit.
> This works fine if you are using virtio_cread interfaces which will swap
> to/from LE for you.
> 
> What doesn't work correctly is shadowing the whole config space
> using ->get since that does not byte-swap. so just don't do it.
> 
> I would say just do what everyone does in this version and
> we can revisit this later.
> 

OK, it's fair. :) 

Thanks!
-Gonglei

> >
> > > > If you want it in LE format, swap it!
> > > >
> > > >
> > > >
> > > > > --
> > > > > 1.8.3.1
> > > > >
> > > >
> > > > ---------------------------------------------------------------------
> > > > To unsubscribe, e-mail: virtio-dev-unsubscribe@...ts.oasis-open.org
> > > > For additional commands, e-mail: virtio-dev-help@...ts.oasis-open.org