[PATCH RFC 11/12] vringh: allow vringh_iov_xfer() to skip bytes when ptr is NULL

Stefano Garzarella
2020-11-13T13:48:53Z

In some cases, it may be useful to provide a way to skip a number
of bytes in a vringh_iov.

In order to keep vringh_iov consistent, let's reuse vringh_iov_xfer()
logic and skip bytes when the ptr is NULL.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---

I'm not sure if this is the best option, maybe we can add a new
function vringh_iov_skip().

Suggestions?
---
drivers/vhost/vringh.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 8bd8b403f087..ed3290946ad7 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -75,7 +75,9 @@ static inline int __vringh_get_head(const struct vringh *vrh,
return head;
}

-/* Copy some bytes to/from the iovec. Returns num copied. */
+/* Copy some bytes to/from the iovec. Returns num copied.
+ * If ptr is NULL, skips at most len bytes.
+ */
static inline ssize_t vringh_iov_xfer(struct vringh *vrh,
struct vringh_kiov *iov,
void *ptr, size_t len,
@@ -89,12 +91,16 @@ static inline ssize_t vringh_iov_xfer(struct vringh *vrh,
size_t partlen;

partlen = min(iov->iov[iov->i].iov_len, len);
- err = xfer(vrh, iov->iov[iov->i].iov_base, ptr, partlen);
- if (err)
- return err;
+
+ if (ptr) {
+ err = xfer(vrh, iov->iov[iov->i].iov_base, ptr, partlen);
+ if (err)
+ return err;
+ ptr += partlen;
+ }
+
done += partlen;
len -= partlen;
- ptr += partlen;
iov->consumed += partlen;
iov->iov[iov->i].iov_len -= partlen;
iov->iov[iov->i].iov_base += partlen;
--
2.26.2