[PATCH net-next v5 0/6] virtio/vsock: introduce MSG_EOR flag for SEQPACKET

From: Arseny Krasnov
Date: Fri Sep 03 2021 - 08:30:57 EST

This patchset implements support of MSG_EOR bit for SEQPACKET
AF_VSOCK sockets over virtio transport.
First we need to define 'messages' and 'records' like this:
Message is result of sending calls: 'write()', 'send()', 'sendmsg()'
etc. It has fixed maximum length, and it bounds are visible using
return from receive calls: 'read()', 'recv()', 'recvmsg()' etc.
Current implementation based on message definition above.
Record has unlimited length, it consists of multiple message,
and bounds of record are visible via MSG_EOR flag returned from
'recvmsg()' call. Sender passes MSG_EOR to sending system call and
receiver will see MSG_EOR when corresponding message will be processed.
Idea of patchset comes from POSIX: it says that SEQPACKET
supports record boundaries which are visible for receiver using
MSG_EOR bit. So, it looks like MSG_EOR is enough thing for SEQPACKET
and we don't need to maintain boundaries of corresponding send -
receive system calls. But, for 'sendXXX()' and 'recXXX()' POSIX says,
that all these calls operates with messages, e.g. 'sendXXX()' sends
message, while 'recXXX()' reads messages and for SEQPACKET, 'recXXX()'
must read one entire message from socket, dropping all out of size
bytes. Thus, both message boundaries and MSG_EOR bit must be supported
to follow POSIX rules.
To support MSG_EOR new bit was added along with existing
'VIRTIO_VSOCK_SEQ_EOR': 'VIRTIO_VSOCK_SEQ_EOM'(end-of-message) - now it
works in the same way as 'VIRTIO_VSOCK_SEQ_EOR'. But 'VIRTIO_VSOCK_SEQ_EOR'
is used to mark 'MSG_EOR' bit passed from userspace.
This patchset includes simple test for MSG_EOR.

Arseny Krasnov(6):
virtio/vsock: rename 'EOR' to 'EOM' bit.
virtio/vsock: add 'VIRTIO_VSOCK_SEQ_EOR' bit.
vhost/vsock: support MSG_EOR bit processing
virtio/vsock: support MSG_EOR bit processing
af_vsock: rename variables in receive loop
vsock_test: update message bounds test for MSG_EOR

drivers/vhost/vsock.c | 28 +++++++++++++----------
include/uapi/linux/virtio_vsock.h | 3 ++-
net/vmw_vsock/af_vsock.c | 10 ++++----
net/vmw_vsock/virtio_transport_common.c | 23 ++++++++++++-------
tools/testing/vsock/vsock_test.c | 8 ++++++-
5 files changed, 45 insertions(+), 27 deletions(-)

v4 -> v5:
- Move bitwise and out of le32_to_cpu() in 0003.

v3 -> v4:
- 'sendXXX()' renamed to 'send*()' in 0002- commit msg.
- Comment about bit restore updated in 0003-.
- 'same' renamed to 'similar' in 0003- commit msg.
- u32 used instead of uint32_t in 0003-.

v2 -> v3:
- 'virtio/vsock: rename 'EOR' to 'EOM' bit.' - commit message updated.
- 'VIRTIO_VSOCK_SEQ_EOR' bit add moved to separate patch.
- 'vhost/vsock: support MSG_EOR bit processing' - commit message
- 'vhost/vsock: support MSG_EOR bit processing' - removed unneeded
'le32_to_cpu()', because input argument was already in CPU

v1 -> v2:
support backward compatibility.
- use bitmask of flags to restore in vhost.c, instead of separated
bool variable for each flag.
- test for EAGAIN removed, as logically it is not part of this
patchset(will be sent separately).
- cover letter updated(added part with POSIX description).

Signed-off-by: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>