utils: Add a manpage for nfbpf_compile

Content is rather sparse, but still better than no manpage at all.

Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 73 insertions, 1 deletions

diff --git a/utils/.gitignore b/utils/.gitignore
index 7c6afbf4..6300812b 100644
--- a/utils/.gitignore
+++ b/utils/.gitignore
@@ -1,3 +1,4 @@
 /nfnl_osf
 /nfnl_osf.8
 /nfbpf_compile
+/nfbpf_compile.8
diff --git a/utils/Makefile.am b/utils/Makefile.am
index 80029e30..d09a6974 100644
--- a/utils/Makefile.am
+++ b/utils/Makefile.am
@@ -17,6 +17,7 @@ nfnl_osf_LDADD = ${libnfnetlink_LIBS}
 endif
 
 if ENABLE_BPFC
+man_MANS += nfbpf_compile.8
 sbin_PROGRAMS += nfbpf_compile
 nfbpf_compile_LDADD = -lpcap
 endif
@@ -26,4 +27,4 @@ sbin_PROGRAMS += nfsynproxy
 nfsynproxy_LDADD = -lpcap
 endif
 
-CLEANFILES = nfnl_osf.8
+CLEANFILES = nfnl_osf.8 nfbpf_compile.8
diff --git a/utils/nfbpf_compile.8.in b/utils/nfbpf_compile.8.in
new file mode 100644
index 00000000..d02979a5
--- /dev/null
+++ b/utils/nfbpf_compile.8.in
@@ -0,0 +1,70 @@
+.TH NFBPF_COMPILE 8 "" "@PACKAGE_STRING@" "@PACKAGE_STRING@"
+
+.SH NAME
+nfbpf_compile \- generate bytecode for use with xt_bpf
+.SH SYNOPSIS
+
+.ad l
+.in +8
+.ti -8
+.B nfbpf_compile
+[
+.I LLTYPE
+]
+.I PROGRAM
+
+.ti -8
+.I LLTYPE
+:= {
+.BR EN10MB " | " RAW " | " SLIP " | "
+.I ...
+}
+
+.SH DESCRIPTION
+The
+.B nfbpf_compile
+utility aids in generating BPF byte code suitable for passing to
+the iptables
+.B bpf
+match.
+
+.SH OPTIONS
+
+.TP
+.I LLTYPE
+Link-layer header type to operate on. This is a name as defined in
+.RB < pcap/dlt.h >
+but with the leading
+.B DLT_
+prefix stripped. For use with iptables,
+.B RAW
+should be the right choice (it's also the default if not specified).
+
+.TP
+.I PROGRAM
+The BPF expression to compile, see
+.BR pcap-filter (7)
+for a description of the language.
+
+.SH EXIT STATUS
+The program returns 0 on success, 1 otherwise.
+
+.SH EXAMPLE
+Match incoming TCP packets with size bigger than 100 bytes:
+.P
+.in +8
+.EE
+bpf=$(nfbpf_compile 'tcp and greater 100')
+.br
+iptables -A INPUT -m bpf --bytecode "$bpf" -j ACCEPT
+.RE
+.P
+The description of
+.B bpf
+match in
+.BR iptables-extensions (8)
+lists a few more examples.
+
+.SH SEE ALSO
+.BR iptables-extensions (8),
+.BR pcap-filter (7)