netdev - Re: [PATCH net-next] pppoe: new ioctl to extract per-channel stats

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Date:   Thu, 26 Mar 2020 14:48:31 +0100
From:   Simon Chopin <s.chopin@...halink.fr>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Networking <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Guillaume Nault <gnault@...hat.com>
Subject: Re: [PATCH net-next] pppoe: new ioctl to extract per-channel stats

(Dropping Michal Ostrowski from the CC list as the address bounces for me)

Le 26/03/2020 à 11:42, Arnd Bergmann a écrit :
> On Thu, Mar 26, 2020 at 11:32 AM Simon Chopin <s.chopin@...halink.fr> wrote:
>> The PPP subsystem uses the abstractions of channels and units, the
>> latter being an aggregate of the former, exported to userspace as a
>> single network interface.  As such, it keeps traffic statistics at the
>> unit level, but there are no statistics on the individual channels,
>> partly because most PPP units only have one channel.
>>
>> However, it is sometimes useful to have statistics at the channel level,
>> for instance to monitor multilink PPP connections. Such statistics
>> already exist for PPPoL2TP via the PPPIOCGL2TPSTATS ioctl, this patch
>> introduces a very similar mechanism for PPPoE via a new
>> PPPIOCGPPPOESTATS ioctl.
>>
>> The contents of this patch were greatly inspired by the L2TP
>> implementation, many thanks to its authors.
> The patch looks fine from from an interface design perspective,
> but I wonder if you could use a definition that matches the
> structure layout and command number for PPPIOCGL2TPSTATS
> exactly, rather than a "very similar mechanism" with a subset
> of the fields. You would clearly have to pass down a number of
> zero fields, but the implementation could be abstracted at a
> higher level later.
>
>       Arnd

This sounds like a good idea, indeed. Is what follows what you had in mind ?
I'm not too sure about keeping the chan_priv field in this form, my knowledge
of alignment issues being relatively superficial. As I understand it, the matching
fields in l2tp_ioc_stats should always be packed to 8 bytes as they fall on natural
boundaries, but I might be wrong ?

  Simon


diff --git a/include/uapi/linux/ppp-ioctl.h b/include/uapi/linux/ppp-ioctl.h
index a0abc68eceb5..803cbe374fb2 100644
--- a/include/uapi/linux/ppp-ioctl.h
+++ b/include/uapi/linux/ppp-ioctl.h
@@ -79,14 +79,21 @@ struct pppol2tp_ioc_stats {
        __aligned_u64   rx_errors;
 };

-/* For PPPIOCGPPPOESTATS */
-struct pppoe_ioc_stats {
+struct pppchan_ioc_stats {
+       __u8            chan_priv[8];
        __aligned_u64   tx_packets;
        __aligned_u64   tx_bytes;
+       __aligned_u64   tx_errors;
        __aligned_u64   rx_packets;
        __aligned_u64   rx_bytes;
+       __aligned_u64   rx_seq_discards;
+       __aligned_u64   rx_oos_packets;
+       __aligned_u64   rx_errors;
 };

+_Static_assert(sizeof(struct pppol2tp_ioc_stats) == sizeof(struct pppchan_ioc_stats), "same size");
+_Static_assert((size_t)&((struct pppol2tp_ioc_stats *)0)->tx_packets == (size_t)&((struct pppchan_ioc_stats *)0)->tx_packets, "same offset");
+
 /*
  * Ioctl definitions.
  */
@@ -123,7 +130,7 @@ struct pppoe_ioc_stats {
 #define PPPIOCATTCHAN  _IOW('t', 56, int)      /* attach to ppp channel */
 #define PPPIOCGCHAN    _IOR('t', 55, int)      /* get ppp channel number */
 #define PPPIOCGL2TPSTATS _IOR('t', 54, struct pppol2tp_ioc_stats)
-#define PPPIOCGPPPOESTATS _IOR('t', 53, struct pppoe_ioc_stats)
+#define PPPIOCGCHANSTATS _IOR('t', 54, struct pppchan_ioc_stats)

 #define SIOCGPPPSTATS   (SIOCDEVPRIVATE + 0)
 #define SIOCGPPPVER     (SIOCDEVPRIVATE + 1)   /* NEVER change this!! */