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From: Paul Durrant <paul@xen.org>
To: xen-devel@lists.xenproject.org
Cc: Juergen Gross <jgross@suse.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Paul Durrant <pdurrant@amazon.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Jan Beulich <jbeulich@suse.com>
Subject: [PATCH v3 1/8] public/io/netif: specify MTU override node
Date: Tue, 11 Aug 2020 09:01:55 +0100
Message-ID: <20200811080202.31163-2-paul@xen.org> (raw)
In-Reply-To: <20200811080202.31163-1-paul@xen.org>

From: Paul Durrant <pdurrant@amazon.com>

There is currently no documentation to state what MTU a frontend should
adertise to its network stack. It has however long been assumed that the
default value of 1500 is correct.

This patch specifies a mechanism to allow the tools to set the MTU via a
xenstore node in the frontend area and states that the absence of that node
means the frontend should assume an MTU of 1500 octets.

NOTE: The Windows PV frontend has used an MTU sampled from the xenstore
      node specified in this patch.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <george.dunlap@citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Julien Grall <julien@xen.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Wei Liu <wl@xen.org>

v2:
 - Add a note in xenstore-paths highlighting the new xenstore node
---
 docs/misc/xenstore-paths.pandoc |  3 +++
 xen/include/public/io/netif.h   | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/docs/misc/xenstore-paths.pandoc b/docs/misc/xenstore-paths.pandoc
index 766e8008dc..5cd5c8a3b9 100644
--- a/docs/misc/xenstore-paths.pandoc
+++ b/docs/misc/xenstore-paths.pandoc
@@ -298,6 +298,9 @@ A virtual keyboard device frontend. Described by
 A virtual network device frontend. Described by
 [xen/include/public/io/netif.h][NETIF]
 
+NOTE: ~/device/vif/$DEVID/mtu can be used to inform the frontend of an
+      increased MTU. (The default MTU is 1500 octets).
+
 #### ~/device/vscsi/$DEVID/* []
 
 A virtual scsi device frontend. Described by
diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index 9fcf91a2fe..00dd258712 100644
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -204,6 +204,18 @@
  * present).
  */
 
+/*
+ * MTU
+ * ===
+ *
+ * The toolstack may set a value of MTU for the frontend by setting the
+ * /local/domain/<domid>/device/vif/<vif>/mtu node with the MTU value in
+ * octets. If this node is absent the frontend should assume an MTU value
+ * of 1500 octets. A frontend is also at liberty to ignore this value so
+ * it is only suitable for informing the frontend that a packet payload
+ * >1500 octets is permitted.
+ */
+
 /*
  * Hash types
  * ==========
-- 
2.20.1



  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-11  8:01 [PATCH v3 0/8] tools: propogate MTU to vif frontends Paul Durrant
2020-08-11  8:01 ` Paul Durrant [this message]
2020-08-14 16:24   ` [PATCH v3 1/8] public/io/netif: specify MTU override node Wei Liu
2020-08-11  8:01 ` [PATCH v3 2/8] tools/hotplug/Linux: re-factor add_to_bridge() in xen-network-common.sh Paul Durrant
2020-08-11  8:01 ` [PATCH v3 3/8] tools/hotplug/Linux: add remove_from_bridge() Paul Durrant
2020-08-11  8:01 ` [PATCH v3 4/8] tools/hotplug/Linux: remove code duplication in vif-bridge Paul Durrant
2020-08-11  8:01 ` [PATCH v3 5/8] libxl: wire the libxl_device_nic 'mtu' value into xenstore Paul Durrant
2020-08-11  8:02 ` [PATCH v3 6/8] tools/hotplug/Linux: modify set_mtu() to optionally use a configured value Paul Durrant
2020-08-11  8:02 ` [PATCH v3 7/8] xl: add 'mtu' option to network configuration Paul Durrant
2020-08-11  8:02 ` [PATCH v3 8/8] remove netchannel2 hotplug script... ancient history Paul Durrant
2020-08-27  9:58 ` [PATCH v3 0/8] tools: propogate MTU to vif frontends Wei Liu
2020-08-28 11:03   ` Durrant, Paul

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