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Remove description of deprecated IP fragment checksum support.

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Since SMPng it wasn't really supported anymore and if it worked
then only by chance.  Only very few drivers ever supported it.

Discussed with:	yongari
MFC after:	2 weeks
This commit is contained in:
Andre Oppermann 2012-11-13 20:52:17 +00:00
parent c60bda17f2
commit 327210de43
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=242998
1 changed files with 1 additions and 56 deletions
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57
share/man/man9/mbuf.9
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@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd April 18, 2011
.Dd November 13, 2012
.Dt MBUF 9
.Os
.\"
@ -1063,45 +1063,6 @@ In this case, the checksum field will be initially
set by the TCP/IP module to the checksum of the pseudo header
defined by the TCP and UDP specifications.
.Pp
For outbound packets which have been fragmented
by the host CPU, the following will also be true,
regardless of the checksum flag settings:
.Bl -bullet -offset indent
.It
all fragments will have the flag
.Dv M_FRAG
set in their
.Va m_flags
field;
.It
the first and the last fragments in the chain will have
.Dv M_FIRSTFRAG
or
.Dv M_LASTFRAG
set in their
.Va m_flags ,
correspondingly;
.It
the first fragment in the chain will have the total number
of fragments contained in its
.Va csum_data
field.
.El
.Pp
The last rule for fragmented packets takes precedence over the one
for a TCP or UDP checksum.
Nevertheless, offloading a TCP or UDP checksum is possible for a
fragmented packet if the flag
.Dv CSUM_IP_FRAGS
is set in the field
.Va ifnet.if_data.ifi_hwassist
associated with the network interface.
However, in this case the interface is expected to figure out
the location of the checksum field within the sequence of fragments
by itself because
.Va csum_data
contains a fragment count instead of a checksum offset value.
.Pp
On input, an interface indicates the actions it has performed
on a packet by setting one or more of the following flags in
.Va csum_flags
@ -1147,22 +1108,6 @@ It is a peculiarity of the algorithm used that the Internet checksum
calculated over any valid packet will be
.Li 0xFFFF
as long as the original checksum field is included.
.Pp
For inbound packets which are IP fragments, all
.Va csum_data
fields will be summed during reassembly to obtain the final checksum
value passed to an upper layer in the
.Va csum_data
field of the reassembled packet.
The
.Va csum_flags
fields of all fragments will be consolidated using logical AND
to obtain the final value for
.Va csum_flags .
Thus, in order to successfully
offload checksum computation for fragmented data,
all fragments should have the same value of
.Va csum_flags .
.Sh STRESS TESTING
When running a kernel compiled with the option
.Dv MBUF_STRESS_TEST ,