Update to reflect current reality.

[skip ci]
We require Linux 2.6.27 or later, and the only configuration option that
applies is CONFIG_PACKET_MMAP, which we require on 2.6.x kernels - 3.x
and later kernels have memory-mapped capture support built in.

diff --git a/doc/README.linux.md b/doc/README.linux.md
index ddca4fecfa9e35cc97d4a2ccc230da235a3036a0..143dff654c859d3e67b3cb2b858826ec9155f035 100644 (file)
--- a/doc/README.linux.md
+++ b/doc/README.linux.md
@@ -1,73 +1,8 @@
-In order for libpcap to be able to capture packets on a Linux system,
-the "packet" protocol must be supported by your kernel.  If it is not,
-you may get error messages such as
+Currently, libpcap supports packet capturing on Linux 2.6.27 and later;
+earlier versions are not supported.
 
-       modprobe: can't locate module net-pf-17
-
-in "/var/adm/messages", or may get messages such as
-
-       socket: Address family not supported by protocol
-
-from applications using libpcap.
-
-You must configure the kernel with the CONFIG_PACKET option for this
-protocol; the following note is from the Linux "Configure.help" file for
-the 2.0[.x] kernel:
-
-       Packet socket
-       CONFIG_PACKET
-         The Packet protocol is used by applications which communicate
-         directly with network devices without an intermediate network
-         protocol implemented in the kernel, e.g. tcpdump. If you want them
-         to work, choose Y.
-
-         This driver is also available as a module called af_packet.o ( =
-         code which can be inserted in and removed from the running kernel
-         whenever you want). If you want to compile it as a module, say M
-         here and read Documentation/modules.txt; if you use modprobe or
-         kmod, you may also want to add "alias net-pf-17 af_packet" to
-         /etc/modules.conf.
-
-and the note for the 2.2[.x] kernel says:
-
-       Packet socket
-       CONFIG_PACKET
-         The Packet protocol is used by applications which communicate
-         directly with network devices without an intermediate network
-         protocol implemented in the kernel, e.g. tcpdump. If you want them
-         to work, choose Y. This driver is also available as a module called
-         af_packet.o ( = code which can be inserted in and removed from the
-         running kernel whenever you want). If you want to compile it as a
-         module, say M here and read Documentation/modules.txt.  You will
-         need to add 'alias net-pf-17 af_packet' to your /etc/conf.modules
-         file for the module version to function automatically.  If unsure,
-         say Y.
-
-In addition, there is an option that, in 2.2 and later kernels, will
-allow packet capture filters specified to programs such as tcpdump to be
-executed in the kernel, so that packets that don't pass the filter won't
-be copied from the kernel to the program, rather than having all packets
-copied to the program and libpcap doing the filtering in user mode.
-
-Copying packets from the kernel to the program consumes a significant
-amount of CPU, so filtering in the kernel can reduce the overhead of
-capturing packets if a filter has been specified that discards a
-significant number of packets.  (If no filter is specified, it makes no
-difference whether the filtering isn't performed in the kernel or isn't
-performed in user mode. :-))
-
-The option for this is the CONFIG_FILTER option; the "Configure.help"
-file says:
-
-       Socket filtering
-       CONFIG_FILTER
-         The Linux Socket Filter is derived from the Berkeley Packet Filter.
-         If you say Y here, user-space programs can attach a filter to any
-         socket and thereby tell the kernel that it should allow or disallow
-         certain types of data to get through the socket. Linux Socket
-         Filtering works on all socket types except TCP for now. See the text
-         file linux/Documentation/networking/filter.txt for more information.
-         If unsure, say N.
+You must configure 2.26.x kernels with the CONFIG_PACKET_MMAP option for
+this protocol.  3.x and later kernels do not require that.
 
 Note that, by default, libpcap will, if libnl is present, build with it;
 it uses libnl to support monitor mode on mac80211 devices.  There is a
@@ -94,13 +29,6 @@ Statistics:
 Statistics reported by pcap are platform specific.  The statistics
 reported by pcap_stats on Linux are as follows:
 
-2.2.x
-=====
-ps_recv   Number of packets that were accepted by the pcap filter
-ps_drop   Always 0, this statistic is not gathered on this platform
-
-2.4.x and later
-=====
 ps_recv   Number of packets that were accepted by the pcap filter
 ps_drop   Number of packets that had passed filtering but were not
           passed on to pcap due to things like buffer shortage, etc.