netdev - RE: [PATCH net-next v7 3/7] gtp: Implement GTP echo request

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Date:   Tue, 22 Feb 2022 21:49:29 +0000
From:   "Drewek, Wojciech" <wojciech.drewek@...el.com>
To:     Harald Welte <laforge@...monks.org>
CC:     Marcin Szycik <marcin.szycik@...ux.intel.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "michal.swiatkowski@...ux.intel.com" 
        <michal.swiatkowski@...ux.intel.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pablo@...filter.org" <pablo@...filter.org>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "osmocom-net-gprs@...ts.osmocom.org" 
        <osmocom-net-gprs@...ts.osmocom.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
Subject: RE: [PATCH net-next v7 3/7] gtp: Implement GTP echo request

Hi Harald,

> -----Original Message-----
> From: Harald Welte <laforge@...monks.org>
> Sent: wtorek, 22 lutego 2022 21:40
> To: Drewek, Wojciech <wojciech.drewek@...el.com>
> Cc: Marcin Szycik <marcin.szycik@...ux.intel.com>; netdev@...r.kernel.org; michal.swiatkowski@...ux.intel.com;
> davem@...emloft.net; kuba@...nel.org; pablo@...filter.org; jiri@...nulli.us; osmocom-net-gprs@...ts.osmocom.org; intel-wired-
> lan@...ts.osuosl.org
> Subject: Re: [PATCH net-next v7 3/7] gtp: Implement GTP echo request
> 
> Hi Wojciech,
> 
> On Tue, Feb 22, 2022 at 09:38:08AM +0000, Drewek, Wojciech wrote:
> 
> > > I think either the Tx and the Rx ard triggered by / notified to userspace,
> > > or you would also do periodic triggering of Tx in the kernel autonomously,
> > > and process the responses.  But at that point then you also need to think
> > > about further consequences, such as counting the number of missed ECHO RESP,
> > > and then notify userspace if that condition "N out of M last responses missed".
> > >
> >
> > I thought that with the GTP device created from ip link, userspace
> > would be unable to receive Echo Response (similar to Echo Request).
> > If it's not the case than I will get rid of handling Echo Response in the
> > next version.
> 
> Well, userspace cannot 'receive' the ECHO response through the UDP socket as
> the UDP socket is hidden in the kernel.  I was thinking of the same mechanism
> you introduce for transmit:  You can trigger the Tx of GTP ECHO REQ via netlink,
> so why shouldn't you receive a notifiation about its completion also via netlink?

How can we notify the userspace that the echo response was received? I thought
that I implemented it with the dumpit callback. Is there a way to send msg to the
userspace using generic netlink interface?
> 
> Just don't think of it as sending an ECHO REQ via netlink, but triggering the tx
> and acknowledging the completion/reception of a related response.
> 
> One of the advantages of the existing mechanism via 'socket is held in userspace'
> is that we don't have to jump through any such hoops or invent strange interfaces:
> The process can just send and receive the messages as usual via UDP socket related
> syscalls.
> 
> --
> - Harald Welte <laforge@...monks.org>           http://laforge.gnumonks.org/
> ============================================================================
> "Privacy in residential applications is a desirable marketing option."
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