netdev - [PATCH net-next v2 0/2] timestamp: control SOF_TIMESTAMPING_RX

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Message-Id: <20240828160145.68805-1-kerneljasonxing@gmail.com>
Date: Thu, 29 Aug 2024 00:01:43 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	dsahern@...nel.org,
	willemb@...gle.com
Cc: netdev@...r.kernel.org,
	Jason Xing <kernelxing@...cent.com>
Subject: [PATCH net-next v2 0/2] timestamp: control SOF_TIMESTAMPING_RX_SOFTWARE feature per socket

From: Jason Xing <kernelxing@...cent.com>

Prior to this series, when one socket is set SOF_TIMESTAMPING_RX_SOFTWARE
which measn the whole system turns on this button, other sockets that only
have SOF_TIMESTAMPING_SOFTWARE will be affected and then print the rx
timestamp information even without SOF_TIMESTAMPING_RX_SOFTWARE flag.
In such a case, the rxtimestamp.c selftest surely fails, please see
testcase 6.

In a normal case, if we only set SOF_TIMESTAMPING_SOFTWARE flag, we
can't get the rx timestamp because there is no path leading to turn on
netstamp_needed_key button in net_enable_timestamp(). That is to say, if
the user only sets SOF_TIMESTAMPING_SOFTWARE, we don't expect we are
able to fetch the timestamp from the skb.

More than this, we can find there are some other ways to turn on
netstamp_needed_key, which will happenly allow users to get tstamp in
the receive path. Please see net_enable_timestamp().

How to solve it?

setsockopt interface is used to control each socket separately but in
this case it is affected by other sockets. For timestamp itself, it's
not feasible to convert netstamp_needed_key into a per-socket button
because when the receive stack just handling the skb from driver doesn't
know which socket the skb belongs to.

According to the original design, we should not use both generation flag
(SOF_TIMESTAMPING_RX_SOFTWARE) and report flag (SOF_TIMESTAMPING_SOFTWARE)
together to test if the application is allowed to receive the timestamp
report in the receive path. But it doesn't hold for receive timestamping
case. We have to make an exception.

So we have to test the generation flag when the applications do recvmsg:
if we set both of flags, it means we want the timestamp; if not, it means
we don't expect to see the timestamp even the skb carries.

As we can see, this patch makes the SOF_TIMESTAMPING_RX_SOFTWARE under
setsockopt control. And it's a per-socket fine-grained now.

v2
Link: https://lore.kernel.org/all/20240825152440.93054-1-kerneljasonxing@gmail.com/
Discussed with Willem
1. update the documentation accordingly
2. add more comments in each patch
3. remove the previous test statements in __sock_recv_timestamp()

Jason Xing (2):
  tcp: make SOF_TIMESTAMPING_RX_SOFTWARE feature per socket
  net: make SOF_TIMESTAMPING_RX_SOFTWARE feature per socket

 Documentation/networking/timestamping.rst |  7 +++++++
 include/net/sock.h                        |  7 ++++---
 net/bluetooth/hci_sock.c                  |  4 ++--
 net/core/sock.c                           |  2 +-
 net/ipv4/ip_sockglue.c                    |  2 +-
 net/ipv4/ping.c                           |  2 +-
 net/ipv4/tcp.c                            | 11 +++++++++--
 net/ipv6/datagram.c                       |  4 ++--
 net/l2tp/l2tp_ip.c                        |  2 +-
 net/l2tp/l2tp_ip6.c                       |  2 +-
 net/nfc/llcp_sock.c                       |  2 +-
 net/rxrpc/recvmsg.c                       |  2 +-
 net/socket.c                              | 11 ++++++++---
 net/unix/af_unix.c                        |  2 +-
 14 files changed, 40 insertions(+), 20 deletions(-)

-- 
2.37.3