Re: [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

From: Jason Wang <jasowang@redhat.com>
To: Yongji Xie <xieyongji@bytedance.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	"Stefano Garzarella" <sgarzare@redhat.com>,
	"Parav Pandit" <parav@nvidia.com>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Christian Brauner" <christian.brauner@canonical.com>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	"Matthew Wilcox" <willy@infradead.org>,
	viro@zeniv.linux.org.uk, "Jens Axboe" <axboe@kernel.dk>,
	bcrl@kvack.org, "Jonathan Corbet" <corbet@lwn.net>,
	"Mika Penttilä" <mika.penttila@nextfour.com>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, kvm@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace
Date: Mon, 12 Apr 2021 15:16:13 +0800	[thread overview]
Message-ID: <dc9a90dd-4f86-988c-c1b5-ac606ce5e14b@redhat.com> (raw)
In-Reply-To: <CACycT3vwATp4+Ao0fjuyeeLQN+xHH=dXF+JUyuitkn4k8hELnA@mail.gmail.com>

在 2021/4/9 下午4:02, Yongji Xie 写道:
>>>>> +};
>>>>> +
>>>>> +struct vduse_dev_config_data {
>>>>> +     __u32 offset; /* offset from the beginning of config space */
>>>>> +     __u32 len; /* the length to read/write */
>>>>> +     __u8 data[VDUSE_CONFIG_DATA_LEN]; /* data buffer used to read/write */
>>>> Note that since VDUSE_CONFIG_DATA_LEN is part of uAPI it means we can
>>>> not change it in the future.
>>>>
>>>> So this might suffcient for future features or all type of virtio devices.
>>>>
>>> Do you mean 256 is no enough here？
>> Yes.
>>
> But this request will be submitted multiple times if config lengh is
> larger than 256. So do you think whether we need to extent the size to
> 512 or larger?

So I think you'd better either:

1) document the limitation (256) in somewhere, (better both uapi and doc)

or

2) make it variable

Thanks

>