[bug#35652] [PATCH] services: dhcp-client: Ignore non-ARP network interfaces.

[bug#35652] [PATCH] services: dhcp-client: Ignore non-ARP network interfaces.

[Marius Bakke]

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Guix,

While testing #35563, I found that "dhcp-client" does not work on a
kernel that has CONFIG_IPV6_SIT=y.

The reason is that the system has a virtual "sit0" interface that is not
capable of ARP traffic, which dhclient does not approve of:

May  9 16:18:37 localhost dhclient: Unsupported device type 776 for "sit0"

You can `modprobe sit` on your system if you want to reproduce the
failure.

The attached patch solves it for me.


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From 7724f24443392fdfc2c075909d9b64350f6578b2 Mon Sep 17 00:00:00 2001
From: Marius Bakke <mbakke@fastmail.com>
Date: Thu, 9 May 2019 17:03:03 +0200
Subject: [PATCH] services: dhcp-client: Ignore interfaces that are not ARP
 capable.

* guix/build/syscalls.scm (IFF_NOARP): New variable.
(arp-network-interface?): New public variable.
* gnu/services/networking.scm (dhcp-client-service-type): Filter interfaces
that do not support the ARP protocol.
---
 gnu/services/networking.scm | 4 +++-
 guix/build/syscalls.scm     | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/gnu/services/networking.scm b/gnu/services/networking.scm
index 03b2c6e1ec..082a85f63d 100644
--- a/gnu/services/networking.scm
+++ b/gnu/services/networking.scm
@@ -190,7 +190,9 @@ fe80::1%lo0 apps.facebook.com\n")
                  ;; interfaces are typically down at this point.  Thus we perform
                  ;; our own interface discovery here.
                  (define valid?
-                   (negate loopback-network-interface?))
+                   (lambda (interface)
+                     (and (arp-network-interface? interface)
+                          (not (loopback-network-interface? interface)))))
                  (define ifaces
                    (filter valid? (all-network-interface-names)))
 
diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index 749616ceb1..74428dbf56 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -104,6 +104,7 @@
             network-interface-netmask
             network-interface-running?
             loopback-network-interface?
+            arp-network-interface?
             network-interface-address
             set-network-interface-netmask
             set-network-interface-up
@@ -1160,6 +1161,7 @@ bytes."
 (define-as-needed IFF_BROADCAST #x2)              ;Broadcast address valid.
 (define-as-needed IFF_LOOPBACK #x8)               ;Is a loopback net.
 (define-as-needed IFF_RUNNING #x40)               ;interface RFC2863 OPER_UP
+(define-as-needed IFF_NOARP #x80)                 ;no ARP protocol
 
 (define IF_NAMESIZE 16)                           ;maximum interface name size
 
@@ -1341,6 +1343,13 @@ interface NAME."
     (close-port sock)
     (not (zero? (logand flags IFF_RUNNING)))))
 
+(define (arp-network-interface? name)
+  "Return true if NAME supports the ARP protocol."
+  (let* ((sock  (socket SOCK_STREAM AF_INET 0))
+         (flags (network-interface-flags sock name)))
+    (close-port sock)
+    (zero? (logand flags IFF_NOARP))))
+
 (define-as-needed (set-network-interface-flags socket name flags)
   "Set the flag of network interface NAME to FLAGS."
   (let ((req (make-bytevector ifreq-struct-size)))
-- 
2.21.0


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[bug#35652] [PATCH] services: dhcp-client: Ignore non-ARP network interfaces.

[Ludovic Courtès]

Hi Marius,

Good catch!

Marius Bakke <mbakke@fastmail.com> skribis:

> From 7724f24443392fdfc2c075909d9b64350f6578b2 Mon Sep 17 00:00:00 2001
> From: Marius Bakke <mbakke@fastmail.com>
> Date: Thu, 9 May 2019 17:03:03 +0200
> Subject: [PATCH] services: dhcp-client: Ignore interfaces that are not ARP
>  capable.
>
> * guix/build/syscalls.scm (IFF_NOARP): New variable.
> (arp-network-interface?): New public variable.
> * gnu/services/networking.scm (dhcp-client-service-type): Filter interfaces
> that do not support the ARP protocol.

Could you make it two patches (one for syscalls.scm, and another one for
the rest)?

Otherwise LGTM, thank you!

Ludo’.

bug#35652: [PATCH] services: dhcp-client: Ignore non-ARP network interfaces.

[Marius Bakke]

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Ludovic Courtès <ludo@gnu.org> writes:

> Hi Marius,
>
> Good catch!
>
> Marius Bakke <mbakke@fastmail.com> skribis:
>
>> From 7724f24443392fdfc2c075909d9b64350f6578b2 Mon Sep 17 00:00:00 2001
>> From: Marius Bakke <mbakke@fastmail.com>
>> Date: Thu, 9 May 2019 17:03:03 +0200
>> Subject: [PATCH] services: dhcp-client: Ignore interfaces that are not ARP
>>  capable.
>>
>> * guix/build/syscalls.scm (IFF_NOARP): New variable.
>> (arp-network-interface?): New public variable.
>> * gnu/services/networking.scm (dhcp-client-service-type): Filter interfaces
>> that do not support the ARP protocol.
>
> Could you make it two patches (one for syscalls.scm, and another one for
> the rest)?
>
> Otherwise LGTM, thank you!

Thanks for the amazingly fast review :-)

Pushed in a0dc97a5..6c2180f5.

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