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Deduce when ethertype field is actually data length

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retu2libc 2024-03-06 02:48:46 -05:00 committed by Arsenic Blood
parent 3809e15849
commit f709dc872a
2 changed files with 12 additions and 10 deletions
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19
src/Home/Net/Protocols/Ethernet.ZC
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@ -27,17 +27,13 @@ U0 EthernetGlobalsInit()
}
}
//TODO: check length , figure out the length+4
U0 EthernetFrameParse(CEthernetFrame *frame_out, U8 *frame, U16 length)
{
//TODO: Check length ! We need to figure out what
//lengths are appropriate
//Shrine also says MemCopy has a
//high overhead. Almost tempted to say that means that a lot
//of the current system should be done with less extra allocation
//altogether, more passing.
//In practice, MemCopy causes the most slowdown on bare-metal.
// Shrine says MemCopy has a high overhead.
// Almost tempted to say that means that a lot
// of the current system should be done with
// less extra allocation altogether, more passing.
// In practice, MemCopy causes the most slowdown on bare-metal.
NetLog("ETHERNET FRAME PARSE: Parsing frame, copying out to frame_out param.");
@ -49,7 +45,10 @@ U0 EthernetFrameParse(CEthernetFrame *frame_out, U8 *frame, U16 length)
frame_out->data = frame + ETHERNET_DATA_OFFSET;
frame_out->length = length - ETHERNET_MAC_HEADER_LENGTH - 4; // He has a comment literally just saying "??". + or - 4?
if (frame_out->ethertype <= ETHERNET_v2_MTU) // check if the field is a length or an ethertype
frame_out->length = frame_out->ethertype;
else
frame_out->length = length - ETHERNET_MAC_HEADER_LENGTH - FCS_LENGTH;
}
U0 EthernetFrameFinish(I64 de_index)

3
src/Home/Net/Utilities/Net.HH
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@ -5,11 +5,14 @@
#define ETHERNET_ETHERTYPE_OFFSET 12
#define ETHERNET_DATA_OFFSET 14
#define MAC_ADDRESS_LENGTH 6
#define FCS_LENGTH 4
/* Ethernet Frame Size.
Linux uses 1544, OSDev and Shrine use 1548. Based on IEEE 802.3as, max frame size was agreed upon as 2000 bytes. */
#define ETHERNET_FRAME_SIZE 2000
#define ETHERNET_v2_MTU 1500
#define HTYPE_ETHERNET 1
#define HLEN_ETHERNET 6
#define PLEN_IPV4 4