Kuniyuki Iwashima wrote:
Compared to TCP, ioctl(SIOCINQ) for AF_UNIX SOCK_STREAM socket is more
expensive, as unix_inq_len() requires iterating through the receive queue
and accumulating skb->len.
Let's cache the value for SOCK_STREAM to a new field during sendmsg()
and recvmsg().
The field is protected by the receive queue lock.
nit: for updates, but the read is taken without the lock held, hence
the WRITE_ONCE/READ_ONCE accessors.
Note that ioctl(SIOCINQ) for SOCK_DGRAM returns the length of the first
skb in the queue.
SOCK_SEQPACKET still requires iterating through the queue because we do
not touch functions shared with unix_dgram_ops. But, if really needed,
we can support it by switching __skb_try_recv_datagram() to a custom
version.
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>