Stefano Garzarella
2023-Jul-06 17:06 UTC
[RFC PATCH v5 14/17] docs: net: description of MSG_ZEROCOPY for AF_VSOCK
On Sat, Jul 01, 2023 at 09:39:44AM +0300, Arseniy Krasnov wrote:>This adds description of MSG_ZEROCOPY flag support for AF_VSOCK type of >socket. > >Signed-off-by: Arseniy Krasnov <AVKrasnov at sberdevices.ru> >--- > Documentation/networking/msg_zerocopy.rst | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > >diff --git a/Documentation/networking/msg_zerocopy.rst b/Documentation/networking/msg_zerocopy.rst >index b3ea96af9b49..34bc7ff411ce 100644 >--- a/Documentation/networking/msg_zerocopy.rst >+++ b/Documentation/networking/msg_zerocopy.rst >@@ -7,7 +7,8 @@ Intro > ====> > The MSG_ZEROCOPY flag enables copy avoidance for socket send calls. >-The feature is currently implemented for TCP and UDP sockets. >+The feature is currently implemented for TCP, UDP and VSOCK (with >+virtio transport) sockets. > > > Opportunity and Caveats >@@ -174,7 +175,7 @@ read_notification() call in the previous snippet. A notification > is encoded in the standard error format, sock_extended_err. > > The level and type fields in the control data are protocol family >-specific, IP_RECVERR or IPV6_RECVERR. >+specific, IP_RECVERR or IPV6_RECVERR (for TCP or UDP socket). > > Error origin is the new type SO_EE_ORIGIN_ZEROCOPY. ee_errno is zero, > as explained before, to avoid blocking read and write system calls on >@@ -201,6 +202,7 @@ undefined, bar for ee_code, as discussed below. > > printf("completed: %u..%u\n", serr->ee_info, serr->ee_data); > >+For VSOCK socket, cmsg_level will be SOL_VSOCK and cmsg_type will be 0.Maybe better to move up, just under the previous change. By the way, should we define a valid type value for vsock (e.g. VSOCK_RECVERR)?> > Deferred copies > ~~~~~~~~~~~~~~~ >@@ -235,12 +237,15 @@ Implementation > Loopback > -------- > >+For TCP and UDP: > Data sent to local sockets can be queued indefinitely if the receive > process does not read its socket. Unbound notification latency is not > acceptable. For this reason all packets generated with MSG_ZEROCOPY > that are looped to a local socket will incur a deferred copy. This > includes looping onto packet sockets (e.g., tcpdump) and tun devices. > >+For VSOCK: >+Data path sent to local sockets is the same as for non-local sockets. > > Testing > ======>@@ -254,3 +259,6 @@ instance when run with msg_zerocopy.sh between a veth pair across > namespaces, the test will not show any improvement. For testing, the > loopback restriction can be temporarily relaxed by making > skb_orphan_frags_rx identical to skb_orphan_frags. >+ >+For VSOCK type of socket example can be found in tools/testing/vsock/ >+vsock_test_zerocopy.c.For VSOCK socket, example can be found in tools/testing/vsock/vsock_test_zerocopy.c (we should leave the entire path on the same line)>-- >2.25.1 >