netdev - MSG_PROBE is not set

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Message-ID: <31436f4a0906140336v241390can463c30d8a576e3a6@mail.gmail.com>
Date:	Sun, 14 Jun 2009 13:36:42 +0300
From:	David Shwatrz <dshwatrz@...il.com>
To:	netdev@...r.kernel.org
Subject: MSG_PROBE is not set

Hello,

There is something which I am confused about: when the MSG_PROBE is set, it
means that you cannot should not send the packet. For example, in
ip_append_data()
(ipv4/ip_output.c). This flag should be used for example for finding MTU, AFAIK.
I grepped under the net subtree and **there is no place** when the MSG_PROBE
is set. There are about 5-6 files where this value is checked under net.

When you send a packet from userspace using from sendmsg(), the third parameter
is flags.

You can pass flags like MSG_OOB, MSG_PEEK and other flags from bits/socket.h.
However, you **cannot** pass a flag as MSG_PROBE, AFAIK.
It does not appear at all in bits/socket.h. It **does** appear in
linux/socket.h, but this header is
part of the kernel-headers package, so you cannot include it in a user
space application even if you want (so it won't compile).

So, what do you have here: (and please correct me if I am wrong):
when sending a packet with sendmsg(), this should be from userspace.
the kernel checks a flag which cannot be set from user space.
for what is this flag at all ? is it justified to remove it ?

Regards,
Ds
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