Stefano Garzarella
2023-Sep-01 12:36 UTC
[PATCH net-next v7 2/4] vsock/virtio: support to send non-linear skb
On Sun, Aug 27, 2023 at 11:54:34AM +0300, Arseniy Krasnov wrote:>For non-linear skb use its pages from fragment array as buffers in >virtio tx queue. These pages are already pinned by 'get_user_pages()' >during such skb creation. > >Signed-off-by: Arseniy Krasnov <avkrasnov at salutedevices.com> >--- > Changelog: > v2 -> v3: > * Comment about 'page_to_virt()' is updated. I don't remove R-b, > as this change is quiet small I guess. > v6 -> v7: > * Move arrays '*sgs' and 'bufs' to 'virtio_vsock' instead of being > local variables. This allows to save stack space in cases of too > big MAX_SKB_FRAGS. > * Add 'WARN_ON_ONCE()' for handling nonlinear skbs - it checks that > linear part of such skb contains only header. > * R-b tag removed due to updates above. > > net/vmw_vsock/virtio_transport.c | 54 +++++++++++++++++++++++++++----- > 1 file changed, 47 insertions(+), 7 deletions(-) > >diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c >index e95df847176b..8636477cf088 100644 >--- a/net/vmw_vsock/virtio_transport.c >+++ b/net/vmw_vsock/virtio_transport.c >@@ -63,6 +63,10 @@ struct virtio_vsock { > > u32 guest_cid; > bool seqpacket_allow; >+I'd add a comment here specifying specifying what we need these fields for and why we put them here (basically Paolo's suggestion).>+ /* +1 is for packet header. */ >+ struct scatterlist *sgs[MAX_SKB_FRAGS + 1]; >+ struct scatterlist bufs[MAX_SKB_FRAGS + 1]; > }; > > static u32 virtio_transport_get_local_cid(void) >@@ -100,8 +104,9 @@ virtio_transport_send_pkt_work(struct work_struct *work) > vq = vsock->vqs[VSOCK_VQ_TX]; > > for (;;) { >- struct scatterlist hdr, buf, *sgs[2]; > int ret, in_sg = 0, out_sg = 0; >+ struct scatterlist **sgs; >+ struct scatterlist *bufs; > struct sk_buff *skb; > bool reply; > >@@ -111,12 +116,47 @@ virtio_transport_send_pkt_work(struct work_struct *work) > > virtio_transport_deliver_tap_pkt(skb); > reply = virtio_vsock_skb_reply(skb); >- >- sg_init_one(&hdr, virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb))); >- sgs[out_sg++] = &hdr; >- if (skb->len > 0) { >- sg_init_one(&buf, skb->data, skb->len); >- sgs[out_sg++] = &buf; >+ sgs = vsock->sgs; >+ bufs = vsock->bufs; >+ sg_init_one(&bufs[out_sg], virtio_vsock_hdr(skb), >+ sizeof(*virtio_vsock_hdr(skb))); >+ sgs[out_sg] = &bufs[out_sg];IIUC `sgs[i]` always contains `&bufs[i]`. Could we initialize it once when we allocate `struct virtio_vsock` in `virtio_vsock_probe`? Of course putting a comment in `struct virtio_vsock` about it. Since we are using them only for out buffers, I'd also rename them in out_sgs and out_bufs. The rest LGTM. Stefano>+ out_sg++; >+ >+ if (!skb_is_nonlinear(skb)) { >+ if (skb->len > 0) { >+ sg_init_one(&bufs[out_sg], skb->data, skb->len); >+ sgs[out_sg] = &bufs[out_sg]; >+ out_sg++; >+ } >+ } else { >+ struct skb_shared_info *si; >+ int i; >+ >+ /* If skb is nonlinear, then its buffer must contain >+ * only header and nothing more. Data is stored in >+ * the fragged part. >+ */ >+ WARN_ON_ONCE(skb_headroom(skb) != sizeof(*virtio_vsock_hdr(skb))); >+ >+ si = skb_shinfo(skb); >+ >+ for (i = 0; i < si->nr_frags; i++) { >+ skb_frag_t *skb_frag = &si->frags[i]; >+ void *va; >+ >+ /* We will use 'page_to_virt()' for the userspace page >+ * here, because virtio or dma-mapping layers will call >+ * 'virt_to_phys()' later to fill the buffer descriptor. >+ * We don't touch memory at "virtual" address of this page. >+ */ >+ va = page_to_virt(skb_frag->bv_page); >+ sg_init_one(&bufs[out_sg], >+ va + skb_frag->bv_offset, >+ skb_frag->bv_len); >+ sgs[out_sg] = &bufs[out_sg]; >+ out_sg++; >+ } > } > > ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL); >-- >2.25.1 >