Re: [PATCH net-next v5 1/4] vsock/virtio/vhost: read data from non-linear skb
From: Paolo Abeni <pabeni@redhat.com>
Date: 2023-08-01 13:12:33
Also in:
kvm, lkml, virtualization
On Sun, 2023-07-30 at 11:59 +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.
It looks like the above sentence is a left-over from previous version as, as this patch does not touch data_len. And I think it contradicts the previous one, so it's a bit confusing.
quoted hunk ↗ jump to hunk
Signed-off-by: Arseniy Krasnov <redacted> --- 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 --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;
IMHO 'offset' would be a better name for both the variable and the CB field, as it can points both inside the skb frags, linear part or frag list. Otherwise LGTM, thanks! Paolo