linux-kernel - Re: [PATCH v4 06/14] vringh: add vringh_kiov

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Date:   Mon, 15 Mar 2021 18:06:07 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Laurent Vivier <lvivier@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Xie Yongji <xieyongji@...edance.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        linux-kernel@...r.kernel.org, Max Gurtovoy <mgurtovoy@...dia.com>,
        Jason Wang <jasowang@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH v4 06/14] vringh: add vringh_kiov_length() helper

On Mon, Mar 15, 2021 at 05:51:30PM +0100, Laurent Vivier wrote:
>On 15/03/2021 17:34, Stefano Garzarella wrote:
>> This new helper returns the total number of bytes covered by
>> a vringh_kiov.
>>
>> Suggested-by: Jason Wang <jasowang@...hat.com>
>> Acked-by: Jason Wang <jasowang@...hat.com>
>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>> ---
>>  include/linux/vringh.h | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/include/linux/vringh.h b/include/linux/vringh.h
>> index 755211ebd195..84db7b8f912f 100644
>> --- a/include/linux/vringh.h
>> +++ b/include/linux/vringh.h
>> @@ -199,6 +199,17 @@ static inline void vringh_kiov_cleanup(struct vringh_kiov *kiov)
>>  	kiov->iov = NULL;
>>  }
>>
>> +static inline size_t vringh_kiov_length(struct vringh_kiov *kiov)
>> +{
>> +	size_t len = 0;
>> +	int i;
>> +
>> +	for (i = kiov->i; i < kiov->used; i++)
>> +		len += kiov->iov[i].iov_len;
>> +
>> +	return len;
>> +}
>
>Do we really need an helper?
>
>For instance, we can use:
>
>len = iov_length((struct iovec *)kiov->iov, kiov->used);
>
>Or do we want to avoid the cast?

Yes, that should be fine. If we want, I can remove the helper and use 
iov_length() directly. I thought vringh wanted to hide iovec from users 
though.

Anyway talking to Jason, as a long term solution we should reconsider 
vringh and support iov_iter.

Thanks,
Stefano