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List:       busybox
Subject:    Ping Sock RcvBuff Error
From:       Sacha Terzian <sterzian24 () gmail ! com>
Date:       2016-03-30 20:18:56
Message-ID: CAHwYn0e5QDXKnDyQTccN9HQK8X3V85rmpjF=a5MJSYSJt4Ukvg () mail ! gmail ! com
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I recently increased my ETHERNET MTU size to 10k+. However I noticed that
busybox ping has stopped working. When I analysed the source code I realised
that in ping4 we do the calculation;

 sockopt = (datalen * 2) + 7 * 1024;

Then we use this calculation to set the rcvbuff size. Is there any
explanation behind this calculation? Also, in my case if the buffer size is
less then approximately my ETHERNET MTU I do not received any replies is
there an explanation behind this?

A temporary patch is to run tests and find out the required RCV BUFF for my
pings to go trough. Once I found this value to force the rcv buff to always
be this size.

[Attachment #5 (text/html)]

<div dir="ltr"><span style="font-size:12.8px">I recently increased my ETHERNET MTU \
size to 10k+. However I noticed that</span><br style="font-size:12.8px"><span \
style="font-size:12.8px">busybox ping has stopped working. When I analysed the source \
code I realised</span><br style="font-size:12.8px"><span \
style="font-size:12.8px">that in ping4 we do the calculation;</span><br \
style="font-size:12.8px"><br style="font-size:12.8px"><span style="font-size:12.8px"> \
sockopt = (datalen * 2) + 7 * 1024;</span><br style="font-size:12.8px"><br \
style="font-size:12.8px"><span style="font-size:12.8px">Then we use this calculation \
to set the rcvbuff size. Is there any</span><br style="font-size:12.8px"><span \
style="font-size:12.8px">explanation behind this calculation? Also, in my case if the \
buffer size is</span><br style="font-size:12.8px"><span style="font-size:12.8px">less \
then approximately my ETHERNET MTU I do not received any replies is</span><br \
style="font-size:12.8px"><span style="font-size:12.8px">there an explanation behind \
this?</span><br style="font-size:12.8px"><br style="font-size:12.8px"><span \
style="font-size:12.8px">A temporary patch is to run tests and find out the required \
RCV BUFF for my</span><br style="font-size:12.8px"><span \
style="font-size:12.8px">pings to go trough. Once I found this value to force the rcv \
buff to always</span><br style="font-size:12.8px"><span style="font-size:12.8px">be \
this size.</span><br></div>



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