linux-kernel - Re: [PATCH v2 1/2] vfio/mdev: add version attribute for mdev device

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Message-ID: <20190514090326.2f4288ae.cohuck@redhat.com>
Date:   Tue, 14 May 2019 09:03:26 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Yan Zhao <yan.y.zhao@...el.com>
Cc:     Erik Skultety <eskultet@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "arei.gonglei@...wei.com" <arei.gonglei@...wei.com>,
        "aik@...abs.ru" <aik@...abs.ru>,
        "Zhengxiao.zx@...baba-inc.com" <Zhengxiao.zx@...baba-inc.com>,
        "shuangtai.tst@...baba-inc.com" <shuangtai.tst@...baba-inc.com>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "eauger@...hat.com" <eauger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yang, Ziye" <ziye.yang@...el.com>,
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        "Liu, Changpeng" <changpeng.liu@...el.com>,
        "Ken.Xue@....com" <Ken.Xue@....com>,
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        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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        "Tian, Kevin" <kevin.tian@...el.com>,
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        "Wang, Zhi A" <zhi.a.wang@...el.com>,
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        "berrange@...hat.com" <berrange@...hat.com>,
        "dinechin@...hat.com" <dinechin@...hat.com>
Subject: Re: [PATCH v2 1/2] vfio/mdev: add version attribute for mdev device

On Tue, 14 May 2019 02:12:35 -0400
Yan Zhao <yan.y.zhao@...el.com> wrote:

> On Mon, May 13, 2019 at 09:28:04PM +0800, Erik Skultety wrote:

> > In case of libvirt checking the compatibility, it won't matter how good the
> > error message in the kernel log is and regardless of how many error states you
> > want to handle, libvirt's only limited to errno here, since we're going to do
> > plain read/write, so our internal error message returned to the user is only
> > going to contain what the errno says - okay, of course we can (and we DO)
> > provide libvirt specific string, further specifying the error but like I
> > mentioned, depending on how many error cases we want to distinguish this may be
> > hard for anyone to figure out solely on the error code, as apps will most
> > probably not parse the
> > logs.
> > 
> > Regards,
> > Erik  
> hi Erik
> do you mean you are agreeing on defining common errors and only returning errno?
> 
> e.g.
> #define ENOMIGRATION         140  /* device not supporting migration */
> #define EUNATCH              49  /* software version not match */
> #define EHWNM                142  /* hardware not matching*/

Defining custom error codes is probably not such a good idea... can we
match to common error codes instead? Do we have a good idea about
common error categories, anyway?

(Btw: does libvirt do a generic error-to-description translation, or
does it match to the context? I.e., can libvirt translate well-defined
error codes to a useful message for a specific case?)