From: Stephen Hemminger <stephen@networkplumber•org>
To: netdev@vger•kernel.org
Subject: Fw: [Bug 54491] New: UFO (UDP fragmentation offload) does not work if the payload size specified is within the range ( (MTU-28) to (MTU-8) )
Date: Tue, 26 Feb 2013 07:46:06 -0800 [thread overview]
Message-ID: <20130226074606.4d16ebfb@nehalam.linuxnetplumber.net> (raw)
Begin forwarded message:
Date: Tue, 26 Feb 2013 00:52:33 -0800
From: "bugzilla-daemon@bugzilla•kernel.org" <bugzilla-daemon@bugzilla•kernel.org>
To: "stephen@networkplumber•org" <stephen@networkplumber•org>
Subject: [Bug 54491] New: UFO (UDP fragmentation offload) does not work if the payload size specified is within the range ( (MTU-28) to (MTU-8) )
https://bugzilla.kernel.org/show_bug.cgi?id=54491
Summary: UFO (UDP fragmentation offload) does not work if the
payload size specified is within the range ( (MTU-28)
to (MTU-8) )
Product: Networking
Version: 2.5
Kernel Version: 3.3.4
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
AssignedTo: shemminger@linux-foundation•org
ReportedBy: hnk437@gmail•com
Regression: No
For IPv4/UDP if the payload size specified is within the range ( (MTU-28)
to (MTU-8) ) packet gets segmented in kernel even if the following netdev
features are set:
NETIF_F_SG
NETIF_F_GEN_CSUM
NETIF_F_UFO
NETIF_F_TSO
NETIF_F_GSO
NETIF_F_GSO_ROBUST
Analysis:
udp_sendmsg() computes packet length by adding UDP header size to payload size:
“ulen += sizeof(struct udphdr)”
Then the function calls ip_make_skb(), however IP header size is not added to
the packet length.
ip_make_skb() in turn calls __ip_append_data(). The same packet length is used
here.
__ip_append_data() compares the packet length with MTU. The packet length still
does not include IP header size (20 bytes).
In result, when payload size “is within the range ( (MTU-28) to (MTU-8) )”
standard branch is taken rather than ip_ufo_append_data(). Gso_size is not
computed, therefore IP fragmentation is triggered from ip_finish_output().
The issue was reproduced on 3.4.3 as well
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next reply other threads:[~2013-02-26 15:46 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-26 15:46 Stephen Hemminger [this message]
2013-02-27 3:20 ` Fw: [Bug 54491] New: UFO (UDP fragmentation offload) does not work if the payload size specified is within the range ( (MTU-28) to (MTU-8) ) Cong Wang
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