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SubjectRe: [PATCH RFC v2 04/10] vringh: implement vringh_kiov_advance()
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On 2021/1/28 下午10:41, Stefano Garzarella wrote:
> In some cases, it may be useful to provide a way to skip a number
> of bytes in a vringh_kiov.
>
> Let's implement vringh_kiov_advance() for this purpose, reusing the
> code from vringh_iov_xfer().
> We replace that code calling the new vringh_kiov_advance().


Acked-by: Jason Wang <jasowang@redhat.com>

In the long run we need to switch to use iov iterator library instead.

Thanks


>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> include/linux/vringh.h | 2 ++
> drivers/vhost/vringh.c | 41 +++++++++++++++++++++++++++++------------
> 2 files changed, 31 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/vringh.h b/include/linux/vringh.h
> index 9c077863c8f6..755211ebd195 100644
> --- a/include/linux/vringh.h
> +++ b/include/linux/vringh.h
> @@ -199,6 +199,8 @@ static inline void vringh_kiov_cleanup(struct vringh_kiov *kiov)
> kiov->iov = NULL;
> }
>
> +void vringh_kiov_advance(struct vringh_kiov *kiov, size_t len);
> +
> int vringh_getdesc_kern(struct vringh *vrh,
> struct vringh_kiov *riov,
> struct vringh_kiov *wiov,
> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> index bee63d68201a..4d800e4f31ca 100644
> --- a/drivers/vhost/vringh.c
> +++ b/drivers/vhost/vringh.c
> @@ -75,6 +75,34 @@ static inline int __vringh_get_head(const struct vringh *vrh,
> return head;
> }
>
> +/**
> + * vringh_kiov_advance - skip bytes from vring_kiov
> + * @iov: an iov passed to vringh_getdesc_*() (updated as we consume)
> + * @len: the maximum length to advance
> + */
> +void vringh_kiov_advance(struct vringh_kiov *iov, size_t len)
> +{
> + while (len && iov->i < iov->used) {
> + size_t partlen = min(iov->iov[iov->i].iov_len, len);
> +
> + iov->consumed += partlen;
> + iov->iov[iov->i].iov_len -= partlen;
> + iov->iov[iov->i].iov_base += partlen;
> +
> + if (!iov->iov[iov->i].iov_len) {
> + /* Fix up old iov element then increment. */
> + iov->iov[iov->i].iov_len = iov->consumed;
> + iov->iov[iov->i].iov_base -= iov->consumed;
> +
> + iov->consumed = 0;
> + iov->i++;
> + }
> +
> + len -= partlen;
> + }
> +}
> +EXPORT_SYMBOL(vringh_kiov_advance);
> +
> /* Copy some bytes to/from the iovec. Returns num copied. */
> static inline ssize_t vringh_iov_xfer(struct vringh *vrh,
> struct vringh_kiov *iov,
> @@ -95,19 +123,8 @@ static inline ssize_t vringh_iov_xfer(struct vringh *vrh,
> done += partlen;
> len -= partlen;
> ptr += partlen;
> - iov->consumed += partlen;
> - iov->iov[iov->i].iov_len -= partlen;
> - iov->iov[iov->i].iov_base += partlen;
>
> - if (!iov->iov[iov->i].iov_len) {
> - /* Fix up old iov element then increment. */
> - iov->iov[iov->i].iov_len = iov->consumed;
> - iov->iov[iov->i].iov_base -= iov->consumed;
> -
> -
> - iov->consumed = 0;
> - iov->i++;
> - }
> + vringh_kiov_advance(iov, partlen);
> }
> return done;
> }

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