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FromDevice -- Click element; reads packets from network device (Linux kernel)
FromDevice(DEVNAME [, keywords PROMISC, BURST, TIMESTAMP...])
Ports: no inputs, 1 output
Package: linuxmodule (core)
This manual page describes the Linux kernel module version of the FromDevice element. For the user-level element, read the FromDevice.u manual page. Intercepts all packets received by the Linux network interface named DEVNAME and pushes them out output 0. The packets include the link-level header. DEVNAME may also be an Ethernet address, in which case FromDevice searches for a device with that address. FromDevice receives packets at interrupt time and stores them in an internal queue. Later, in the Click kernel thread -- that is, not at interrupt time -- a FromDevice task emits packets from that queue into the configuration. It emits at most BURST packets per task execution; BURST is 8 by default. Keyword arguments are:
Linux won't see any packets from the device. If you want Linux to process packets, you should hand them to ToHost. FromDevice accesses packets the same way Linux does: through interrupts. This is bad for performance. If you care about performance and have a polling-capable device, use PollDevice instead. Linux device drivers should have set packets' timestamp, packet-type, and device annotations, so packets emitted by FromDevice generally have these annotations.
On patchless installations, FromDevice works by repurposing the hooks used for Ethernet bridging. It is not advised to use FromDevice and the Ethernet bridge module simultaneously. On patched installations, FromDevice intercepts packets before they are passed to packet sniffers like tcpdump. However, on patchless installations, packet sniffers receive incoming packets before FromDevice can intercept them. This means that in a configuration such as
FromDevice(eth0) -> ToHost;
packet sniffers will see eth0's packets twice, once before FromDevice runs and once when the packets are handed back to Linux via ToHost.
Generated by 'click-elem2man' from '../elements/linuxmodule/fromdevice.hh:5' on 12/Jul/2011.