UMEM without a FILL ring

[Baruch-Fridman]

xdp-tools/lib/libxdp/xsk.c

Line 319 in 84d3c95

if (!umem_area || !umem_ptr || !fill || !comp)

Why is it not possible to create UMEM without a FILL ring for use in TX only?
Why is it different from the socket that is possible?

xdp-tools/lib/libxdp/xsk.c

Line 1036 in 84d3c95

if (!umem || !xsk_ptr || !(rx || tx))

[magnus-karlsson]

Good question. The code in the kernel does not allow for this and I do not remember exactly the reason, but probably something about code simplicity since a umem can be shared between multiple different sockets. You can always make the unwanted ring small :-).