diff mbox series

[net-next,v4,1/4] vsock/virtio/vhost: read data from non-linear skb

Message ID 20230727222627.1895355-2-AVKrasnov@sberdevices.ru (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series vsock/virtio/vhost: MSG_ZEROCOPY preparations | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1328 this patch: 1328
netdev/cc_maintainers warning 1 maintainers not CCed: xuanzhuo@linux.alibaba.com
netdev/build_clang success Errors and warnings before: 1351 this patch: 1351
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1351 this patch: 1351
netdev/checkpatch warning WARNING: line length of 83 exceeds 80 columns WARNING: line length of 85 exceeds 80 columns WARNING: line length of 91 exceeds 80 columns WARNING: line length of 93 exceeds 80 columns
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Arseniy Krasnov July 27, 2023, 10:26 p.m. UTC
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@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.
 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()'.

 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(-)
diff mbox series

Patch

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 352d042b130b..0b6a89139810 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -364,9 +364,10 @@  virtio_transport_stream_do_peek(struct vsock_sock *vsk,
 		spin_unlock_bh(&vvs->rx_lock);
 
 		/* sk_lock is held by caller so no one else can dequeue.
-		 * Unlock rx_lock since memcpy_to_msg() may sleep.
+		 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 		 */
-		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;
 
@@ -410,25 +411,27 @@  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.
+		 * Unlock rx_lock since skb_copy_datagram_iter() 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);
@@ -492,9 +495,10 @@  virtio_transport_seqpacket_do_peek(struct vsock_sock *vsk,
 			spin_unlock_bh(&vvs->rx_lock);
 
 			/* sk_lock is held by caller so no one else can dequeue.
-			 * Unlock rx_lock since memcpy_to_msg() may sleep.
+			 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 			 */
-			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)
 				return err;
 
@@ -553,11 +557,13 @@  static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 				int err;
 
 				/* sk_lock is held by caller so no one else can dequeue.
-				 * Unlock rx_lock since memcpy_to_msg() may sleep.
+				 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 				 */
 				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.