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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. 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> Link: https://patch.msgid.link/20250702223606.1054680-5-kuniyu@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>