Thanks a bunch Dave ! The vlib_buffer_add_data(...) does the trick for me ! All that I really had to do was to just set up the following fields in the vlib_buffer_t for the buffer index created by the function vnet_buffer (b)->sw_if_index[VLIB_RX] vnet_buffer (b)->sw_if_index[VLIB_TX]
What a nice function ! On Mon, Oct 29, 2018 at 4:50 AM Dave Barach (dbarach) <dbar...@cisco.com> wrote: > > 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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