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 Thu, 17 Nov 2022 11:26:58 +0000 (UTC)
From: "Tobias Fiebig" <tobias@fiebig.nl>
To: "'Stefan Hajnoczi'" <stefanha@gmail.com>
Cc: "'Jason Wang'" <jasowang@redhat.com>,
 "'Stefan Hajnoczi'" <stefanha@redhat.com>, <qemu-devel@nongnu.org>,
 <qemu-stable@nongnu.org>,
 "'Russell King - ARM Linux'" <linux@armlinux.org.uk>
References: <20221115163659.1595865-1-stefanha@redhat.com>
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Subject: RE: [PATCH for-7.2] rtl8139: honor large send MSS value
Date: Thu, 17 Nov 2022 12:26:57 +0100
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Heho,
Ok, that explains a lot. I was also thinking that the vlan bit seem to =
overlap with the MTU field, and wanted to look at that later today.

Re the 12b: IIRC, the standard 1500 MTU for ethernet is already without =
the ethernet header; That can have up to 26b (18b basis, 4b 802.1q, 4b =
802.1ad), but leads to a total frame length of 1526 (with other =
additions (MPLS) also just making the frame bigger, without touching the =
MTU/MSS). MSS than as usual -40 for v4 and ~ -60 for v6.

So I doubt that those 12b are subtracted for the ethernet header.

Does somebody still have an RTL8139 around, to test how the real =
hardware behaved?

With best regards,
Tobias

-----Original Message-----
From: Stefan Hajnoczi <stefanha@gmail.com>=20
Sent: Thursday, 17 November 2022 12:16
To: Tobias Fiebig <tobias@fiebig.nl>
Cc: Jason Wang <jasowang@redhat.com>; Stefan Hajnoczi =
<stefanha@redhat.com>; qemu-devel@nongnu.org; qemu-stable@nongnu.org; =
Russell King - ARM Linux <linux@armlinux.org.uk>
Subject: Re: [PATCH for-7.2] rtl8139: honor large send MSS value

After looking more closely at txdw0 it seems that the code mixes "Tx =
command mode 0", "Tx command mode 1", and "Tx status mode". The bits =
have different meanings in each mode, so this leads to confusion :).

Stefan