KernelTun: Use IFF_NO_PI on Linux, remove LINUX_ETHERTAP mode #397
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This commit adds flag IFF_NO_PI to tun/tap interface settings on Linux. It flag changes frame format in order not to include protocol information header. That is, with this flag, frames received/send from tun/tap fd consist solely of raw underlying protocol (Ethernet/IP) frames. Protocol information header is not used by the element in any way, but its presence adds a requirement for pulling packet data on receive and pushing it before writing packet to the fd. Such a push becomes an expensive push when there is is no enough headroom in packet, for example when using native netmap buffers which do not have headroom. Adding IFF_NO_PI flag eliminates the need for pulling and pushing packet data completely. Moreover, this commit removes support for LINUX_ETHERTAP mode. Ethertap driver was removed from the kernel more than 15 years ago. Removal of this mode significantly simplifies the logic within the element.
tbarbette
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May 3, 2018
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Nice !
I'll ingrate this in FastClick also if I may, no matter waht this PR becomes here.
I've been working on this element recently to provide batch compatibility and (limited) multi-threading.
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Tom, does the multi-threading that you are working on add kerneltap multiqueue support? |
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Yes it's the idea. Following the FastClick's FromDPDKDevice idea, the element spawns one task per threads that reads from the TAP device. I'll finish it now. |
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This commit adds flag IFF_NO_PI to tun/tap interface settings on Linux. It changes frame format in order not to include protocol information header. That is, with this flag, frames received/send from tun/tap fd consist solely of raw underlying protocol (Ethernet/IP) frames.
Protocol information header is not used by the element in any way, but its presence adds a requirement for pulling packet data on receive and pushing it before writing packet to the fd. Such a push becomes an expensive push when there is is no enough headroom in packet, for example when using native netmap buffers, which do not have any headroom.
Adding IFF_NO_PI flag eliminates the need for pulling and pushing packet data completely.
Moreover, this commit removes support for LINUX_ETHERTAP mode. Ethertap driver was removed from the kernel more than 15 years ago. Removal of this mode significantly simplifies the logic within the element.