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Message-ID: <0d79442d-438b-4960-8daf-2f178a210e64@linux.dev>
Date: Mon, 2 Sep 2024 20:40:51 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Willem de Bruijn <willemb@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>,
netdev@...r.kernel.org, Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH net-next v2 1/2] net_tstamp: add SCM_TS_OPT_ID to provide
OPT_ID in control message
On 02/09/2024 16:51, Willem de Bruijn wrote:
> Jason Xing wrote:
>> On Mon, Sep 2, 2024 at 9:09 PM Vadim Fedorenko <vadfed@...a.com> wrote:
>>>
>>> SOF_TIMESTAMPING_OPT_ID socket option flag gives a way to correlate TX
>>> timestamps and packets sent via socket. Unfortunately, there is no way
>>> to reliably predict socket timestamp ID value in case of error returned
>>> by sendmsg. For UDP sockets it's impossible because of lockless
>>> nature of UDP transmit, several threads may send packets in parallel. In
>>> case of RAW sockets MSG_MORE option makes things complicated. More
>>> details are in the conversation [1].
>>> This patch adds new control message type to give user-space
>>> software an opportunity to control the mapping between packets and
>>> values by providing ID with each sendmsg. This works fine for UDP
>>> sockets only, and explicit check is added to control message parser.
>>>
>>> [1] https://lore.kernel.org/netdev/CALCETrU0jB+kg0mhV6A8mrHfTE1D1pr1SD_B9Eaa9aDPfgHdtA@mail.gmail.com/
>>>
>>> Signed-off-by: Vadim Fedorenko <vadfed@...a.com>
>>> ---
>>> Documentation/networking/timestamping.rst | 14 ++++++++++++++
>>> arch/alpha/include/uapi/asm/socket.h | 4 +++-
>>> arch/mips/include/uapi/asm/socket.h | 2 ++
>>> arch/parisc/include/uapi/asm/socket.h | 2 ++
>>> arch/sparc/include/uapi/asm/socket.h | 2 ++
>>> include/net/inet_sock.h | 4 +++-
>>> include/net/sock.h | 1 +
>>> include/uapi/asm-generic/socket.h | 2 ++
>>> include/uapi/linux/net_tstamp.h | 3 ++-
>>> net/core/sock.c | 12 ++++++++++++
>>> net/ethtool/common.c | 1 +
>>> net/ipv4/ip_output.c | 16 ++++++++++++----
>>> net/ipv6/ip6_output.c | 16 ++++++++++++----
>>> 13 files changed, 68 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/Documentation/networking/timestamping.rst b/Documentation/networking/timestamping.rst
>>> index 5e93cd71f99f..93b0901e4e8e 100644
>>> --- a/Documentation/networking/timestamping.rst
>>> +++ b/Documentation/networking/timestamping.rst
>>> @@ -193,6 +193,20 @@ SOF_TIMESTAMPING_OPT_ID:
>>> among all possibly concurrently outstanding timestamp requests for
>>> that socket.
>>>
>>> + With this option enabled user-space application can provide custom
>>> + ID for each message sent via UDP socket with control message with
>>> + type set to SCM_TS_OPT_ID::
>>> +
>>> + struct msghdr *msg;
>>> + ...
>>> + cmsg = CMSG_FIRSTHDR(msg);
>>> + cmsg->cmsg_level = SOL_SOCKET;
>>> + cmsg->cmsg_type = SO_TIMESTAMPING;
>>> + cmsg->cmsg_len = CMSG_LEN(sizeof(__u32));
>>> + *((__u32 *) CMSG_DATA(cmsg)) = opt_id;
>>> + err = sendmsg(fd, msg, 0);
>>> +
>>> +
>>> SOF_TIMESTAMPING_OPT_ID_TCP:
>>> Pass this modifier along with SOF_TIMESTAMPING_OPT_ID for new TCP
>>> timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the
>>> diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
>>> index e94f621903fe..0698e6662cdf 100644
>>> --- a/arch/alpha/include/uapi/asm/socket.h
>>> +++ b/arch/alpha/include/uapi/asm/socket.h
>>> @@ -10,7 +10,7 @@
>>> * Note: we only bother about making the SOL_SOCKET options
>>> * same as OSF/1, as that's all that "normal" programs are
>>> * likely to set. We don't necessarily want to be binary
>>> - * compatible with _everything_.
>>> + * compatible with _everything_.
>>> */
>>> #define SOL_SOCKET 0xffff
>>>
>>> @@ -140,6 +140,8 @@
>>> #define SO_PASSPIDFD 76
>>> #define SO_PEERPIDFD 77
>>>
>>> +#define SCM_TS_OPT_ID 78
>>> +
>>> #if !defined(__KERNEL__)
>>>
>>> #if __BITS_PER_LONG == 64
>>> diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
>>> index 60ebaed28a4c..bb3dc8feb205 100644
>>> --- a/arch/mips/include/uapi/asm/socket.h
>>> +++ b/arch/mips/include/uapi/asm/socket.h
>>> @@ -151,6 +151,8 @@
>>> #define SO_PASSPIDFD 76
>>> #define SO_PEERPIDFD 77
>>>
>>> +#define SCM_TS_OPT_ID 78
>>> +
>>> #if !defined(__KERNEL__)
>>>
>>> #if __BITS_PER_LONG == 64
>>> diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
>>> index be264c2b1a11..c3ab3b3289eb 100644
>>> --- a/arch/parisc/include/uapi/asm/socket.h
>>> +++ b/arch/parisc/include/uapi/asm/socket.h
>>> @@ -132,6 +132,8 @@
>>> #define SO_PASSPIDFD 0x404A
>>> #define SO_PEERPIDFD 0x404B
>>>
>>> +#define SCM_TS_OPT_ID 0x404C
>>> +
>>> #if !defined(__KERNEL__)
>>>
>>> #if __BITS_PER_LONG == 64
>>> diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
>>> index 682da3714686..9b40f0a57fbc 100644
>>> --- a/arch/sparc/include/uapi/asm/socket.h
>>> +++ b/arch/sparc/include/uapi/asm/socket.h
>>> @@ -133,6 +133,8 @@
>>> #define SO_PASSPIDFD 0x0055
>>> #define SO_PEERPIDFD 0x0056
>>>
>>> +#define SCM_TS_OPT_ID 0x0057
>>> +
>>> #if !defined(__KERNEL__)
>>>
>>>
>>> diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
>>> index 394c3b66065e..2161d50cf0fd 100644
>>> --- a/include/net/inet_sock.h
>>> +++ b/include/net/inet_sock.h
>>> @@ -174,6 +174,7 @@ struct inet_cork {
>>> __s16 tos;
>>> char priority;
>>> __u16 gso_size;
>>> + u32 ts_opt_id;
>>> u64 transmit_time;
>>> u32 mark;
>>> };
>>> @@ -241,7 +242,8 @@ struct inet_sock {
>>> struct inet_cork_full cork;
>>> };
>>>
>>> -#define IPCORK_OPT 1 /* ip-options has been held in ipcork.opt */
>>> +#define IPCORK_OPT 1 /* ip-options has been held in ipcork.opt */
>>> +#define IPCORK_TS_OPT_ID 2 /* timestmap opt id has been provided in cmsg */
>>>
>>> enum {
>>> INET_FLAGS_PKTINFO = 0,
>>> diff --git a/include/net/sock.h b/include/net/sock.h
>>> index f51d61fab059..73e21dad5660 100644
>>> --- a/include/net/sock.h
>>> +++ b/include/net/sock.h
>>> @@ -1794,6 +1794,7 @@ struct sockcm_cookie {
>>> u64 transmit_time;
>>> u32 mark;
>>> u32 tsflags;
>>> + u32 ts_opt_id;
>>> };
>>>
>>> static inline void sockcm_init(struct sockcm_cookie *sockc,
>>> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
>>> index 8ce8a39a1e5f..db3df3e74b01 100644
>>> --- a/include/uapi/asm-generic/socket.h
>>> +++ b/include/uapi/asm-generic/socket.h
>>> @@ -135,6 +135,8 @@
>>> #define SO_PASSPIDFD 76
>>> #define SO_PEERPIDFD 77
>>>
>>> +#define SCM_TS_OPT_ID 78
>>> +
>>> #if !defined(__KERNEL__)
>>>
>>> #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
>>> diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
>>> index a2c66b3d7f0f..e2f145e3f3a1 100644
>>> --- a/include/uapi/linux/net_tstamp.h
>>> +++ b/include/uapi/linux/net_tstamp.h
>>> @@ -32,8 +32,9 @@ enum {
>>> SOF_TIMESTAMPING_OPT_TX_SWHW = (1<<14),
>>> SOF_TIMESTAMPING_BIND_PHC = (1 << 15),
>>> SOF_TIMESTAMPING_OPT_ID_TCP = (1 << 16),
>>> + SOF_TIMESTAMPING_OPT_ID_CMSG = (1 << 17),
>>
>> I'm not sure if the new flag needs to be documented as well? After
>> this patch, people may search the key word in the documentation file
>> and then find nothing.
>>
>> If we have this flag here, normally it means we can pass it through
>> setsockopt, so is it expected? If it's an exception, I reckon that we
>> can forbid passing/setting this option in sock_set_timestamping() and
>> document this rule?
>
> Good point, thanks.
>
> It must definitely not be part of SOF_TIMESTAMPING_MASK. My bad for
> suggesting without giving it much thought.
>
> The bit is kernel-internal. No need to even mention it in user-facing
> documentation. But anyone reading net_tstamp.h might wonder what it
> does.
>
> It should not even be in a UAPI header, but in an internal one.
> Probably include/net/sock.h, near SK_FLAGS_TIMESTAMP.
>
> Maybe we can reserve bit 31 in u32 sk_tsflags. And if we ever have
> to double that flag size, it can move up to 63, as it is not UAPI in
> any way. This is a workaround to having a separate flags field in
> sockcm_cookie.
>
> And have a BUILD_BUG_ON if SOF_TIMESTAMPING_LAST reaches this reserved
> region.
Yeah, I was also thinking of it not being UAPI, that's why I tried to
avoid it in my RFC using 0 as a reserved value. Do you think
SK_FLAGS_CMSG_TS_OPT_ID is good naming for it?
Thanks,
Vadim
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