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SubjectRe: [PATCH RFC v2 04/10] vringh: implement vringh_kiov_advance()
On Mon, Feb 01, 2021 at 01:43:23PM +0800, Jason Wang wrote:
>
>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.

Yes I agree.
I've tried to do this, but it requires quite a bit of work to change
vringh, I'll put it on my todo list.

Thanks,
Stefano

>
>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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