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Kernel: Set MSS option for outbound TCP SYN packets

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When the MSS option header is missing the default maximum segment
size is 536 which results in lots of very small TCP packets that
NetworkTask has to handle.

This adds the MSS option header to outbound TCP SYN packets and
sets it to an appropriate value depending on the interface's MTU.

Note that we do not currently do path MTU discovery so this could
cause problems when hops don't fragment packets properly.
This commit is contained in:
Gunnar Beutner 2021-05-11 21:09:11 +02:00 • committed by Andreas Kling
parent 5feeb62843
commit aff4d22de9
3 changed files with 40 additions and 16 deletions
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17
Kernel/Net/TCP.h
View file

@ -21,6 +21,23 @@ struct TCPFlags {
};
};
class [[gnu::packed]] TCPOptionMSS {
public:
TCPOptionMSS(u16 value)
: m_value(value)
{
}
u16 value() const { return m_value; }
private:
u8 m_option_kind { 0x02 };
u8 m_option_length { sizeof(TCPOptionMSS) };
NetworkOrdered<u16> m_value;
};
static_assert(sizeof(TCPOptionMSS) == 4);
class [[gnu::packed]] TCPPacket {
public:
TCPPacket() = default;