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is transmitted as all ones". This got broken after introduction of delayed checksums as follows. Some guys (including Jonathan) think that it is allowed to transmit all ones in place of a zero checksum for TCP the same way as for UDP. (The discussion still takes place on -net.) Thus, the 0 -> 0xffff checksum fixup was first moved from udp_output() (see udp_usrreq.c, 1.64 -> 1.65) to in_cksum_skip() (see sys/i386/i386/in_cksum.c, 1.17 -> 1.18, INVERT expression). Besides that I disagree that it is valid for TCP, there was no real problem until in_cksum.c,v 1.20, where the in_cksum() was made just a special version of in_cksum_skip(). The side effect was that now every incoming IP datagram failed to pass the checksum test (in_cksum() returned 0xffff when it should actually return zero). It was fixed next day in revision 1.21, by removing the INVERT expression. The latter also broke the 0 -> 0xffff fixup for UDP checksums. Before this change: : tcpdump: listening on lo0 : 127.0.0.1.33005 > 127.0.0.1.33006: udp 0 (ttl 64, id 1) : 4500 001c 0001 0000 4011 7cce 7f00 0001 : 7f00 0001 80ed 80ee 0008 0000 After this change: : tcpdump: listening on lo0 : 127.0.0.1.33005 > 127.0.0.1.33006: udp 0 (ttl 64, id 1) : 4500 001c 0001 0000 4011 7cce 7f00 0001 : 7f00 0001 80ed 80ee 0008 ffff |
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| bin | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| kerberosIV | ||
| lib | ||
| libexec | ||
| release | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| COPYRIGHT | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.upgrade | ||
| README | ||
| UPDATING | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you have to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/i386/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/User commands. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberosIV Kerberos package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/handbook/synching.html