Look at .../src/vnet/ipfix-export/flow_report.c : send_template_packet(...) for
a decent example of most of the mechanics involved. Also look at
.../src/vlib/buffer.c : vlib_buffer_add_data(...).
If you're going to send lots of such packets, it may well improve performance
to allocate a fair number of buffers at a time, and maintain a private buffer
cache. See ../src/vnet/tcp/tcp_output.c : tcp_alloc_tx_buffers(...).
HTH... Dave
-----Original Message-----
From: vpp-dev@lists.fd.io <vpp-dev@lists.fd.io> On Behalf Of Prashant Upadhyaya
Sent: Sunday, October 28, 2018 3:13 AM
To: vpp-dev@lists.fd.io
Subject: [vpp-dev] Regarding vlib_buffer_t construction for tx of a self-made
packet
Hi,
I have a situation where one of my plugins needs to construct an l2 packet
(containing an ip datagram inside).
So I have a local buffer which contains the following bytes laid out -- dst mac
src mac ethertype ip header + payload
Assume for the sake of generality that the above buffer is 4K bytes (because I
have an ip payload of that much size) Assume further that I magically already
know the sw if indices of the RX and TX.
It is also ensured that the l2 paylod size is lesser than or equal to the MTU
of the TX interface
Now once I have all of the above information, I need to create a vlib_buffer_t
(possibly a chained set) So I need some guidelines/best practices of how to go
about it flawlessly so that once the vlib_buffer_t is constructed, I can simply
send it to the "interface-output" and accomplish the act of transmission.
The high level set of things that I can think of is --
1. Allocate a vlib_buffer_t (or a chained flavour of those) 2. Start appending
data to those buffers 3. What about the various control fields to be set in the
above buffers ?
. I suppose I will have to do the following --
vnet_buffer (b0)->sw_if_index[VLIB_RX] = <My known index>;
vnet_buffer (b0)->sw_if_index[VLIB_TX] = <My known index>; Do I
need to do anything with b0->buffer_pool_index ?
What to do with b0->current_data ?
What to do with b0->flags ?
What to do with b->current_length ?
And if it is a chained set, what is to be done on individual vlib_buffer_t of
the chain and what on the first one of the chain ?
I suppose I need a convenience function like the following
vlib_buffer_t* foo(char* myl2packet, int lengthOfMyL2Packet, u32 mySwIfRxIndex,
u32 mySwIfTxIndex)
The above should return to me a nice little vlib_buffer_t (possibly
chained) which I can then ship to interface output.
I am willing to write such a function by all means but want to find out if
anything like this (or closer) already exists.
If it doesn't exist, what idioms can I follow from the functions which already
exist and what I have to be careful about.
Regards
-Prashant
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