Re: [PATCH v2] Enable retrieving of RTNET network packet timestamp OOB using recvmsg()

["François Legal" <devel@thom.fr.eu.org>]

Le Lundi, Juillet 26, 2021 14:01 CEST, Jan Kiszka <jan.kiszka@siemens.com> a écrit:

> On 17.05.21 11:44, François Legal via Xenomai wrote:
> > This patch enables retrieving, in realtime application, of RTNET enabled adapters packet timestamps.
> > It uses the linux semantic SO_TIMESTAMPNS, and the linux code to put the timestamp in the control_msg structure.
> >
> > I tested this patch with af_packet sockets only. UDP  & TCP might be a little bit trickier as many fragment/segments get reassembled in a single recvmsg. I believe the linux code I used to put the timestamps in the control structure should be OK though.
>
> One of my question on v1 is still open: How does Linux handle stamping
> the context of fragmented UDP and TCP packets? And given that you enable
> it for those protocols as well, we should likely test that too.

I thought I already gave an answer to this. Sorry.
Linux does not handle time stamping of UDP and TCP as far as I understand.
I certainly plan to use the UDP timestamping feature at some point in the future, but maybe I can exclude UDP and TCP for the moment, and stick to af_packet which has be tested by myself. I'll resubmit another patch with (at least) udp support whenever I need it and have time to test it.

What do you think ?

François

>
> >
> > Signed-off-by: François LEGAL <devel@thom.fr.eu.org>
> > ---
> >  kernel/drivers/net/stack/Kconfig              |  8 +++
> >  .../drivers/net/stack/include/rtnet_socket.h  |  7 +++
> >  kernel/drivers/net/stack/ipv4/tcp/tcp.c       |  8 +++
> >  kernel/drivers/net/stack/ipv4/udp/udp.c       |  7 +++
> >  kernel/drivers/net/stack/packet/af_packet.c   |  7 +++
> >  kernel/drivers/net/stack/socket.c             | 59 +++++++++++++++++++
> >  6 files changed, 96 insertions(+)
> >
> > diff --git a/kernel/drivers/net/stack/Kconfig b/kernel/drivers/net/stack/Kconfig
> > index 830cec5ad..f8ee0f1ad 100644
> > --- a/kernel/drivers/net/stack/Kconfig
> > +++ b/kernel/drivers/net/stack/Kconfig
> > @@ -12,6 +12,14 @@ config XENO_DRIVERS_NET_RX_FIFO_SIZE
> >      of two! Effectively, only CONFIG_RTNET_RX_FIFO_SIZE-1 slots will
> >      be usable.
> >
> > +config XENO_DRIVERS_NET_PACKET_TIMESTAMP
> > +    bool "Enable packet timestamping (SO_TIMESTAMPNS)"
> > +    depends on XENO_DRIVERS_NET
> > +    ---help---
> > +    Enable userland access to low level packet timestamps using SO_TIMESTAMPNS
> > +    ioctl on socket. Timestamp are then returned in recvmsg calls in msg_control
> > +    structure inside msghdr structure.
> > +
>
> Why do we need a config option? All it adds in the off-case is a single
> bit test.
>
> >  config XENO_DRIVERS_NET_ETH_P_ALL
> >      depends on XENO_DRIVERS_NET
> >      bool "Support for ETH_P_ALL"
> > diff --git a/kernel/drivers/net/stack/include/rtnet_socket.h b/kernel/drivers/net/stack/include/rtnet_socket.h
> > index d2caab649..dc488a58a 100644
> > --- a/kernel/drivers/net/stack/include/rtnet_socket.h
> > +++ b/kernel/drivers/net/stack/include/rtnet_socket.h
> > @@ -29,6 +29,7 @@
> >
> >  #include <asm/atomic.h>
> >  #include <linux/list.h>
> > +#include <net/sock.h>
> >
> >  #include <rtdev.h>
> >  #include <rtdm/net.h>
> > @@ -77,6 +78,12 @@ struct rtsocket {
> >  	} prot;
> >  };
> >
> > +#ifdef CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP
> > +#define SOCKET_FLAG_TIMESTAMP   SOCK_RCVTSTAMPNS
> > +int rtnet_put_cmsg(struct rtdm_fd *fd, struct user_msghdr *msg, int level,
> > +					int type, int len, void *data);
> > +#endif
> > +
> >  static inline struct rtdm_fd *rt_socket_fd(struct rtsocket *sock)
> >  {
> >  	return rtdm_private_to_fd(sock);
> > diff --git a/kernel/drivers/net/stack/ipv4/tcp/tcp.c b/kernel/drivers/net/stack/ipv4/tcp/tcp.c
> > index d8c189c88..c8b21c521 100644
> > --- a/kernel/drivers/net/stack/ipv4/tcp/tcp.c
> > +++ b/kernel/drivers/net/stack/ipv4/tcp/tcp.c
> > @@ -2027,6 +2027,14 @@ static ssize_t rt_tcp_read(struct rtdm_fd *fd, void *buf, size_t nbyte)
> >  			kfree_rtskb(first_skb); /* or store the data? */
> >  			return -EFAULT;
> >  		}
> > +
> > +#ifdef CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP
> > +		if (test_bit(SOCKET_FLAG_TIMESTAMP, &sock->flags))
> > +			rtnet_put_cmsg(fd, msg, SOL_SOCKET, SCM_TIMESTAMPNS,
> > +					sizeof(nanosecs_abs_t),
> > +					(void *) &skb->time_stamp);
> > +#endif /* CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP */
> > +
> >  		rtdm_lock_get_irqsave(&ts->socket_lock, context);
> >  		if (ts->sync.window) {
> >  			ts->sync.window += block_size;
> > diff --git a/kernel/drivers/net/stack/ipv4/udp/udp.c b/kernel/drivers/net/stack/ipv4/udp/udp.c
> > index 546b35855..ac6448027 100644
> > --- a/kernel/drivers/net/stack/ipv4/udp/udp.c
> > +++ b/kernel/drivers/net/stack/ipv4/udp/udp.c
> > @@ -463,6 +463,13 @@ ssize_t rt_udp_recvmsg(struct rtdm_fd *fd, struct user_msghdr *msg,
> >  	do {
> >  		rtskb_trim(skb, data_len);
> >
> > +#ifdef CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP
> > +		if (test_bit(SOCKET_FLAG_TIMESTAMP, &sock->flags))
> > +			rtnet_put_cmsg(fd, msg, SOL_SOCKET, SCM_TIMESTAMPNS,
> > +					sizeof(nanosecs_abs_t),
> > +					(void *) &skb->time_stamp);
> > +#endif /* CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP */
> > +
> >  		block_size = skb->len;
> >  		copied += block_size;
> >  		data_len -= block_size;
> > diff --git a/kernel/drivers/net/stack/packet/af_packet.c b/kernel/drivers/net/stack/packet/af_packet.c
> > index cc7487303..10e8113fe 100644
> > --- a/kernel/drivers/net/stack/packet/af_packet.c
> > +++ b/kernel/drivers/net/stack/packet/af_packet.c
> > @@ -364,6 +364,13 @@ static ssize_t rt_packet_recvmsg(struct rtdm_fd *fd, struct user_msghdr *msg,
> >  	if (rtdm_fd_to_context(fd)->device->driver->socket_type != SOCK_DGRAM)
> >  		rtskb_push(rtskb, rtskb->data - rtskb->mac.raw);
> >
> > +#ifdef CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP
> > +		if (test_bit(SOCKET_FLAG_TIMESTAMP, &sock->flags))
> > +			rtnet_put_cmsg(fd, msg, SOL_SOCKET, SCM_TIMESTAMPNS,
> > +					sizeof(nanosecs_abs_t),
> > +					(void *) &rtskb->time_stamp);
> > +#endif /* CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP */
> > +
> >  	/* The data must not be longer than the available buffer size */
> >  	copy_len = rtskb->len;
> >  	len = rtdm_get_iov_flatlen(iov, msg->msg_iovlen);
> > diff --git a/kernel/drivers/net/stack/socket.c b/kernel/drivers/net/stack/socket.c
> > index f030663be..5a9702975 100644
> > --- a/kernel/drivers/net/stack/socket.c
> > +++ b/kernel/drivers/net/stack/socket.c
> > @@ -273,6 +273,15 @@ int rt_socket_if_ioctl(struct rtdm_fd *fd, int request, void __user *arg)
> >  		return rtnet_put_arg(fd, &u_ifc->ifc_len, &size, sizeof(size));
> >  	}
> >
> > +#ifdef CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP
> > +	if (request == SO_TIMESTAMPNS) {
> > +		struct rtsocket *sock = rtdm_fd_to_private(fd);
> > +
> > +		set_bit(SOCKET_FLAG_TIMESTAMP, &sock->flags);
> > +		return 0;
> > +	}
> > +#endif
> > +
> >  	u_ifr = arg;
> >  	ifr = rtnet_get_arg(fd, &_ifr, u_ifr, sizeof(_ifr));
> >  	if (IS_ERR(ifr))
> > @@ -393,3 +402,53 @@ int rtnet_put_arg(struct rtdm_fd *fd, void *dst, const void *src, size_t len)
> >  	return rtdm_copy_to_user(fd, dst, src, len);
> >  }
> >  EXPORT_SYMBOL_GPL(rtnet_put_arg);
> > +
> > +#ifdef CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP
> > +int rtnet_put_cmsg(struct rtdm_fd *fd, struct user_msghdr *msg, int level,
> > +					int type, int len, void *data)
> > +{
> > +	struct cmsghdr __user *cm = msg->msg_control;
> > +	struct cmsghdr cmhdr;
> > +	int cmlen = CMSG_LEN(len);
> > +	int err;
> > +
> > +	if (MSG_CMSG_COMPAT & msg->msg_flags)
> > +		return 0; /* XXX: return error? check spec. */
> > +
> > +	if ((cm == NULL) || (msg->msg_controllen < sizeof(*cm))) {
> > +		msg->msg_flags |= MSG_CTRUNC;
> > +		return 0; /* XXX: return error? check spec. */
>
> Please resolve the "XXX" cases. The first one indicates that this does
> not work with 32-bit compat apps.
>
> > +	}
> > +	if (msg->msg_controllen < cmlen) {
> > +		msg->msg_flags |= MSG_CTRUNC;
> > +		cmlen = msg->msg_controllen;
> > +	}
> > +	cmhdr.cmsg_level = level;
> > +	cmhdr.cmsg_type = type;
> > +	cmhdr.cmsg_len = cmlen;
> > +
> > +	err = -EFAULT;
> > +
> > +	if (!rtdm_fd_is_user(fd)) {
> > +		memcpy(cm, &cmhdr, sizeof(struct cmsghdr));
> > +		memcpy(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr));
> > +		err = 0;
>
> This path does not update msg like below.
>
> > +	} else {
> > +		if (rtdm_copy_to_user(fd, cm, &cmhdr, sizeof(struct cmsghdr)))
> > +			goto out;
> > +		if (rtdm_copy_to_user(fd, CMSG_DATA(cm), data,
> > +					cmlen - sizeof(struct cmsghdr)))
> > +			goto out;
>
> Could also be folded into a "if (... || ...)".
>
> > +		cmlen = CMSG_SPACE(len);
> > +		if (msg->msg_controllen < cmlen)
> > +			cmlen = msg->msg_controllen;
> > +		msg->msg_control += cmlen;
> > +		msg->msg_controllen -= cmlen;
> > +		err = 0;
> > +	}
> > +out:
> > +	return err;
> > +}
> > +EXPORT_SYMBOL(rtdm_put_cmsg);
> > +
> > +#endif /* CONFIG_XENO_DRIVERS_NET_PACKET_TIMESTAMP */
> >
>
> Jan
>
> --
> Siemens AG, T RDA IOT
> Corporate Competence Center Embedded Linux