Bug 2785 – TapBridge::ReceiveFromBridgedDevice(): Write error on Linux >= 4.4

Bug 2785 - TapBridge::ReceiveFromBridgedDevice(): Write error on Linux >= 4.4


Summary:	TapBridge::ReceiveFromBridgedDevice(): Write error on Linux >= 4.4

Status:	NEEDINFO

Product:	ns-3
Classification:	Unclassified
Component:	tap-bridge
Version:	ns-3-dev
Hardware:	All All

Importance:	P3 normal
Assigned To:	Tom Goff

URL:
Keywords:

Depends on:
Blocks:
	Show dependency tree / graph

Reported:	2017-09-25 19:10 EDT by Piotr Jurkiewicz
Modified:	2017-10-03 19:46 EDT (History)
CC List:	2 users (show)

See Also:

Attachments
tap-bridge: Ignore EIO on write (898 bytes, text/plain) 2017-09-25 19:10 EDT, Piotr Jurkiewicz	Details
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Description Piotr Jurkiewicz 2017-09-25 19:10:49 EDT

Created attachment 2925 [details]
tap-bridge: Ignore EIO on write

Since Linux upstream commit 1bd4978a88ac("tun: honor IFF_UP in tun_get_user()"), included in 4.4, writing to a tap device that is not up sets errno to EIO.

Before 4.4 it did no result in error, packets written to an uninitialized tap device were silently dropped.

https://github.com/torvalds/linux/commit/1bd4978a88ac

Due to this change, ns-3 with TapBridge randomly crashes on startup when it tries to write to a device which is not yet UP with the following error:

aborted. cond="bytesWritten != p->GetSize ()", msg="TapBridge::ReceiveFromBridgedDevice(): Write error.", file=../src/tap-bridge/model/tap-bridge.cc, line=994

Similar problem: https://mail.openvswitch.org/pipermail/ovs-dev/2016-June/316261.html

The attached patch fixes the problem by ignoring EIO on write to tap interface. It also adds initialization for previously uninitialized m_linkUp variable.

Comment 1 Tom Henderson 2017-10-03 19:46:17 EDT

Piotr, should we be ignoring the error (is it masking a real failure to use the device)?