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The Berkeley Packet Filter (BPF) provides on some Unix-like systems a raw interface to data link layers, permitting raw link-layer packets to be sent and received. In addition, if the driver for the network interface supports promiscuous mode, it allows the interface to be put into that mode so that all packets on the network can be received, even those destined to other hosts. In addition, it supports "filtering" packets, so that only "interesting" packets will be supplied to the software using BPF; this can avoid copying "uninteresting" packets from the operating system kernel to software running in user mode, reducing the CPU requirement to capture packets and the buffer space required to avoid dropping packets. BPF is sometimes used to refer just to the filtering mechanism, rather than to the entire interface. == Overview == BPF's filtering capabilities are implemented as an interpreter for a machine language for the BPF virtual machine; programs in that language can fetch data from the packet, perform arithmetic operations on data from the packet, and compare the results against constants or against data in the packet or test bits in the results, accepting or rejecting the packet based on the results of those tests. On some platforms, including FreeBSD and WinPcap, just-in-time compilation is used to convert virtual machine instructions into native code in order to further avoid overhead. Kernel-mode interpreters for that same virtual machine language are used in raw data link layer mechanisms in other operating systems, such as Tru64 Unix, and for socket filters in the Linux kernel and in the WinPcap packet capture mechanism. Since version 3.18 of the Linux kernel mainline, possibilities of its embedded BPF virtual machine, referred to as extended BPF or eBPF for short, are extended to allow its use with non-networking parts of the kernel, such as by attaching eBPF programs to various tracepoints. Since kernel version 3.19, eBPF filters can be attached to sockets, and, since kernel version 4.1, to traffic control classifiers. A user-mode interpreter for it is provided with the libpcap/WinPcap implementation of the pcap application programming interface (API), so that, when capturing packets on systems without kernel-mode support for that filtering mechanism, packets can be filtered in user mode; code using the pcap API will work on both types of systems, although, on systems where the filtering is done in user mode, all packets, including those that will be filtered out, are copied from the kernel to user space. That interpreter can also be used when reading a file containing packets captured using pcap. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Berkeley Packet Filter」の詳細全文を読む スポンサード リンク
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