Re: [PATCH net-next v7 1/4] vsock/virtio/vhost: read data from non-linear skb

[Stefano Garzarella]

On Sun, Aug 27, 2023 at 11:54:33AM +0300, Arseniy Krasnov wrote:
> This is preparation patch for MSG_ZEROCOPY support. It adds handling of
> non-linear skbs by replacing direct calls of 'memcpy_to_msg()' with
> 'skb_copy_datagram_iter()'. Main advantage of the second one is that it
> can handle paged part of the skb by using 'kmap()' on each page, but if
> there are no pages in the skb, it behaves like simple copying to iov
> iterator. This patch also adds new field to the control block of skb -
> this value shows current offset in the skb to read next portion of data
> (it doesn't matter linear it or not). Idea behind this field is that
> 'skb_copy_datagram_iter()' handles both types of skb internally - it
> just needs an offset from which to copy data from the given skb. This
> offset is incremented on each read from skb. This approach allows to
> simplify handling of both linear and non-linear skbs, because for
> linear skb we need to call 'skb_pull()' after reading data from it,
> while in non-linear case we need to update 'data_len'.
>
> Signed-off-by: Arseniy Krasnov <avkrasnov@xxxxxxxxxxxxxxxxx>
> ---
> Changelog:
> v5(big patchset) -> v1:
>  * Merge 'virtio_transport_common.c' and 'vhost/vsock.c' patches into
>    this single patch.
>  * Commit message update: grammar fix and remark that this patch is
>    MSG_ZEROCOPY preparation.
>  * Use 'min_t()' instead of comparison using '<>' operators.
> v1 -> v2:
>  * R-b tag added.
> v3 -> v4:
>  * R-b tag removed due to rebase:
>    * Part for 'virtio_transport_stream_do_peek()' is changed.
>    * Part for 'virtio_transport_seqpacket_do_peek()' is added.
>  * Comments about sleep in 'memcpy_to_msg()' now describe sleep in
>    'skb_copy_datagram_iter()'.
> v5 -> v6:
>  * Commit message update.
>  * Rename 'frag_off' to 'offset' in 'virtio_vsock_skb_cb'.
>
> drivers/vhost/vsock.c                   | 14 +++++++----
> include/linux/virtio_vsock.h            |  1 +
> net/vmw_vsock/virtio_transport_common.c | 32 +++++++++++++++----------
> 3 files changed, 29 insertions(+), 18 deletions(-)

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>