[lwip-devel] [bug #49914] lwip_sendmsg uses PBUF_REF pbufs

[Joel Cunningham]

Follow-up Comment #9, bug #49914 (project lwip):

Dirk,

My products/systems currently fit the case you are describing as "large
systems with OS and socket API that have non-DMA HW".  

Without going into extreme detail, my products aren't functioning like the
simple case of direct copy to Ethernet HW buffers you describe.  The link
layer does in fact operate asynchronously with a queue and the transmit path
can't currently handle scatter/gather or pbuf types, so I have copy the entire
packet from the pbuf chain into a contiguous allocation.  This is all done in
the netif output function, so from LwIP's perspective, the output is
synchronous.

Thinking about this some more, it's probably not very common to have the case
you describe where large OS with sockets writing out directly to HW buffers
without some link layer queue.  Given that, the question comes down to: Do we
want to keep the extra flexibility provided by the PBUF_REF case at the
expense of all asynchronous netif developers?

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