--- Begin Message ---El mar., 22 oct. 2019 a las 16:02, Guy Harris (<ghar...@sonic.net>) escribió: > I.e., the goal for libpcap support on Linux should be something such as > > it should work on min({kernel for oldest supported enterprise > distribution}, {oldest "longterm maintenance" kernel release from kernel.org}) > I'm more inclined to oldest longterm from kernel.org only, but I guess so.> OK, so TPACKET_V3 currently supports something similar to what BPF devices > support, i.e. "deliver a block if it's full or if the timeout expires". The > timeout is in the tp_retire_blk_tov field of a tpacket_req3 structure, as > handed to a SOL_PACKET/PACKET_RX_RING setsockopt() call. It's in units of > milliseconds; it doesn't refer to inter-packet spacing, but to the age of the > block. > > Currently it doesn't deliver empty blocks; libpcap can handle either > "delivers empty blocks" (as that's what BPF devices do) or "doesn't deliver > empty blocks" (as that's what TPACKET_V3 currently does). > > The main difference is whether the timeout times out even if no packets are > available; I guess code that wants to be woken up periodically, perhaps to do > other work, even if there's no traffic that passes the filter would prefer > "time out even if no packets are available". > I see. We would want a way to signal we want time outs regardless of blocks being empty, then, right? > OK, I guess I'll have to go back to reading that list. (It's a very heavy > traffic list, and 99.99999999999% of it isn't relevant to packet capture - > all that matters to me is 1) PF_PACKET stuff and 2) stuff involving device > modes such as some ethtool features and monitor-mode/radiotap support - so I > just look at it on occasion.) > Wouldn't CC'ing you keep you on the loop already? > I.e., getifaddr() will find interfaces with no networking-layer addresses (no > IPv4/IPv6/etc.) on 2.4 and later kernels? > Exactly. There's even a code sample showing this in the Linux manual.
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