[RFC,v1,00/16] Improve SOCK_SEQPACKET receive logic

Message

Arseny Krasnov June 28, 2021, 9:59 a.m. UTC

This patchset modifies receive logic for SOCK_SEQPACKET.
Difference between current implementation and this version is that
now reader is woken up when there is at least one RW packet in rx
queue of socket and data is copied to user's buffer, while merged
approach wake up user only when whole message is received and kept
in queue. New implementation has several advantages:
 1) There is no limit for message length. Merged approach requires
    that length must be smaller than 'peer_buf_alloc', otherwise
    transmission will stuck.
 2) There is no need to keep whole message in queue, thus no
    'kmalloc()' memory will be wasted until EOR is received.

    Also new approach has some feature: as fragments of message
are copied until EOR is received, it is possible that part of
message will be already in user's buffer, while rest of message
still not received. And if user will be interrupted by signal or
timeout with part of message in buffer, it will exit receive loop,
leaving rest of message in queue. To solve this problem special
callback was added to transport: it is called when user was forced
to leave exit loop and tells transport to drop any packet until
EOR met. When EOR is found, this mode is disabled and normal packet
processing started. Note, that when 'drop until EOR' mode is on,
incoming packets still inserted in queue, reader will be woken up,
tries to copy data, but nothing will be copied until EOR found.
It was possible to drain such unneeded packets it rx work without
kicking user, but implemented way is simplest. Anyway, i think
such cases are rare.

    New test also added - it tries to copy to invalid user's
buffer.

Arseny Krasnov (16):
 vhost/vsock: don't set 'seqpacket_has_data()' callback
 vsock/loopback: don't set 'seqpacket_has_data()' callback
 virtio/vsock: don't set 'seqpacket_has_data()' callback
 virtio/vsock: remove 'virtio_transport_seqpacket_has_data'
 af_vsock: use SOCK_STREAM function to check data
 vsock/virtio: remove record size limit for SEQPACKET
 virtio/vsock: don't count EORs on receive
 af_vsock: change SEQPACKET receive loop
 af_vsock/virtio: update dequeue callback interface
 virtio/vsock: update SEQPACKET dequeue logic
 afvsock: add 'seqpacket_drop()'
 virtio/vsock: add 'drop until EOR' logic
 vhost/vsock: enable 'seqpacket_drop' callback in transport
 virtio/vsock: enable 'seqpacket_drop' callback in transport
 vsock/loopback: enable 'seqpacket_drop' callback in transport
 vsock_test: SEQPACKET read to broken buffer

 drivers/vhost/vsock.c                   |   2 +-
 include/linux/virtio_vsock.h            |   7 +-
 include/net/af_vsock.h                  |   4 +-
 net/vmw_vsock/af_vsock.c                |  44 ++++----
 net/vmw_vsock/virtio_transport.c        |   2 +-
 net/vmw_vsock/virtio_transport_common.c | 103 +++++++-----------
 net/vmw_vsock/vsock_loopback.c          |   2 +-
 tools/testing/vsock/vsock_test.c        | 121 ++++++++++++++++++++++
 8 files changed, 194 insertions(+), 91 deletions(-)

Signed-off-by: Arseny Krasnov <[e-mail]>