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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/networking/filter.txt
downloadlinux-stericsson-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+filter.txt: Linux Socket Filtering
+Written by: Jay Schulist <jschlst@samba.org>
+
+Introduction
+============
+
+ Linux Socket Filtering is derived from the Berkeley
+Packet Filter. There are some distinct differences between
+the BSD and Linux Kernel Filtering.
+
+Linux Socket Filtering (LSF) allows a user-space program to
+attach a filter onto any socket and allow or disallow certain
+types of data to come through the socket. LSF follows exactly
+the same filter code structure as the BSD Berkeley Packet Filter
+(BPF), so referring to the BSD bpf.4 manpage is very helpful in
+creating filters.
+
+LSF is much simpler than BPF. One does not have to worry about
+devices or anything like that. You simply create your filter
+code, send it to the kernel via the SO_ATTACH_FILTER ioctl and
+if your filter code passes the kernel check on it, you then
+immediately begin filtering data on that socket.
+
+You can also detach filters from your socket via the
+SO_DETACH_FILTER ioctl. This will probably not be used much
+since when you close a socket that has a filter on it the
+filter is automagically removed. The other less common case
+may be adding a different filter on the same socket where you had another
+filter that is still running: the kernel takes care of removing
+the old one and placing your new one in its place, assuming your
+filter has passed the checks, otherwise if it fails the old filter
+will remain on that socket.
+
+Examples
+========
+
+Ioctls-
+setsockopt(sockfd, SOL_SOCKET, SO_ATTACH_FILTER, &Filter, sizeof(Filter));
+setsockopt(sockfd, SOL_SOCKET, SO_DETACH_FILTER, &value, sizeof(value));
+
+See the BSD bpf.4 manpage and the BSD Packet Filter paper written by
+Steven McCanne and Van Jacobson of Lawrence Berkeley Laboratory.