Stefano Garzarella
2023-Jul-18 13:48 UTC
[PATCH net-next v1 1/4] vsock/virtio/vhost: read data from non-linear skb
On Tue, Jul 18, 2023 at 12:00:48AM +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 >avoid special handling of non-linear skbs: >1) We can't call 'skb_pull()' on it, because it updates 'data' pointer. >2) We need to update 'data_len' also on each read from this skb. > >Signed-off-by: Arseniy Krasnov <AVKrasnov at sberdevices.ru> >--- > 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.Reviewed-by: Stefano Garzarella <sgarzare at redhat.com>> > drivers/vhost/vsock.c | 14 ++++++++----- > include/linux/virtio_vsock.h | 1 + > net/vmw_vsock/virtio_transport_common.c | 27 ++++++++++++++++--------- > 3 files changed, 28 insertions(+), 14 deletions(-) > >diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c >index 817d377a3f36..8c917be32b5d 100644 >--- a/drivers/vhost/vsock.c >+++ b/drivers/vhost/vsock.c >@@ -114,6 +114,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock, > struct sk_buff *skb; > unsigned out, in; > size_t nbytes; >+ u32 frag_off; > int head; > > skb = virtio_vsock_skb_dequeue(&vsock->send_pkt_queue); >@@ -156,7 +157,8 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock, > } > > iov_iter_init(&iov_iter, ITER_DEST, &vq->iov[out], in, iov_len); >- payload_len = skb->len; >+ frag_off = VIRTIO_VSOCK_SKB_CB(skb)->frag_off; >+ payload_len = skb->len - frag_off; > hdr = virtio_vsock_hdr(skb); > > /* If the packet is greater than the space available in the >@@ -197,8 +199,10 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock, > break; > } > >- nbytes = copy_to_iter(skb->data, payload_len, &iov_iter); >- if (nbytes != payload_len) { >+ if (skb_copy_datagram_iter(skb, >+ frag_off, >+ &iov_iter, >+ payload_len)) { > kfree_skb(skb); > vq_err(vq, "Faulted on copying pkt buf\n"); > break; >@@ -212,13 +216,13 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock, > vhost_add_used(vq, head, sizeof(*hdr) + payload_len); > added = true; > >- skb_pull(skb, payload_len); >+ VIRTIO_VSOCK_SKB_CB(skb)->frag_off += payload_len; > total_len += payload_len; > > /* If we didn't send all the payload we can requeue the packet > * to send it with the next available buffer. > */ >- if (skb->len > 0) { >+ if (VIRTIO_VSOCK_SKB_CB(skb)->frag_off < skb->len) { > hdr->flags |= cpu_to_le32(flags_to_restore); > > /* We are queueing the same skb to handle >diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h >index c58453699ee9..17dbb7176e37 100644 >--- a/include/linux/virtio_vsock.h >+++ b/include/linux/virtio_vsock.h >@@ -12,6 +12,7 @@ > struct virtio_vsock_skb_cb { > bool reply; > bool tap_delivered; >+ u32 frag_off; > }; > > #define VIRTIO_VSOCK_SKB_CB(skb) ((struct virtio_vsock_skb_cb *)((skb)->cb)) >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >index b769fc258931..1a376f808ae6 100644 >--- a/net/vmw_vsock/virtio_transport_common.c >+++ b/net/vmw_vsock/virtio_transport_common.c >@@ -355,7 +355,7 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk, > spin_lock_bh(&vvs->rx_lock); > > skb_queue_walk_safe(&vvs->rx_queue, skb, tmp) { >- off = 0; >+ off = VIRTIO_VSOCK_SKB_CB(skb)->frag_off; > > if (total == len) > break; >@@ -370,7 +370,10 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk, > */ > spin_unlock_bh(&vvs->rx_lock); > >- err = memcpy_to_msg(msg, skb->data + off, bytes); >+ err = skb_copy_datagram_iter(skb, off, >+ &msg->msg_iter, >+ bytes); >+ > if (err) > goto out; > >@@ -413,25 +416,28 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk, > while (total < len && !skb_queue_empty(&vvs->rx_queue)) { > skb = skb_peek(&vvs->rx_queue); > >- bytes = len - total; >- if (bytes > skb->len) >- bytes = skb->len; >+ bytes = min_t(size_t, len - total, >+ skb->len - VIRTIO_VSOCK_SKB_CB(skb)->frag_off); > > /* sk_lock is held by caller so no one else can dequeue. > * Unlock rx_lock since memcpy_to_msg() may sleep. > */ > spin_unlock_bh(&vvs->rx_lock); > >- err = memcpy_to_msg(msg, skb->data, bytes); >+ err = skb_copy_datagram_iter(skb, >+ VIRTIO_VSOCK_SKB_CB(skb)->frag_off, >+ &msg->msg_iter, bytes); >+ > if (err) > goto out; > > spin_lock_bh(&vvs->rx_lock); > > total += bytes; >- skb_pull(skb, bytes); > >- if (skb->len == 0) { >+ VIRTIO_VSOCK_SKB_CB(skb)->frag_off += bytes; >+ >+ if (skb->len == VIRTIO_VSOCK_SKB_CB(skb)->frag_off) { > u32 pkt_len = le32_to_cpu(virtio_vsock_hdr(skb)->len); > > virtio_transport_dec_rx_pkt(vvs, pkt_len); >@@ -503,7 +509,10 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk, > */ > spin_unlock_bh(&vvs->rx_lock); > >- err = memcpy_to_msg(msg, skb->data, bytes_to_copy); >+ err = skb_copy_datagram_iter(skb, 0, >+ &msg->msg_iter, >+ bytes_to_copy); >+ > if (err) { > /* Copy of message failed. Rest of > * fragments will be freed without copy. >-- >2.25.1 >