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Subject[PATCH v3 05/13] vringh: implement vringh_kiov_advance()
Date
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>
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 2a88e087afd8..4af8fa259d65 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;
}
--
2.29.2
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