3.10. Apply a patch from someone else
Sometimes you need to apply a patch to your private source tree. Maybe
because you want to try a patch from someone on the developer mailing
list, or you want to check your own patch before submitting.
If you have problems applying a patch, make sure the line endings (CR/NL)
of the patch and your source files match.
Given the file "new.diff" containing a unified diff, the right way to
call the patch tool depends on what the pathnames in "new.diff" look like.
If they're relative to the top-level source directory - for example, if a
patch to "prefs.c" just has "prefs.c" as the file name - you'd run it as:
patch -p0 <new.diff
If they're relative to a higher-level directory, you'd replace 0 with the
number of higher-level directories in the path, e.g. if the names are
"wireshark.orig/prefs.c" and "wireshark.mine/prefs.c", you'd run it with:
patch -p1 <new.diff
If they're relative to a
of the top-level
directory, you'd run "patch" in
directory and run
it with "-p0".
If you run it without "-p" at all, the patch tool flattens path names, so
that if you
have a patch file with patches to "Makefile.am" and "wiretap/Makefile.am",
it'll try to apply the first patch to the top-level "Makefile.am" and then
apply the "wiretap/Makefile.am" patch to the top-level "Makefile.am" as
At which position in the filesystem should the patch tool be called?
If the pathnames are relative to the top-level source directory, or to a
directory above that directory, you'd run it in the top-level source
If they're relative to a
- for example,
if somebody did a patch to "packet-ip.c" and ran "diff" or "svn diff" in
the "epan/dissectors" directory - you'd run it in that subdirectory.
It is preferred that people
submit patches like
that - especially if they're only patching files that exist in multiple
directories, such as "Makefile.am".
3.10.2. CVS diff (obsolete)
One other thing to note - "cvs diff" produces output that at least some
versions of "patch" can't handle; you'd get something such as
RCS file: /tcpdump/master/tcpdump/missing/dlnames.c,v
retrieving revision 1.5
diff -c -r1.5 dlnames.c
*** missing/dlnames.c 18 Nov 2003 23:09:43 -0000 1.5
--- missing/dlnames.c 31 Aug 2004 21:45:16 -0000
from "cvs diff -c", and something similar from "cvs diff -u", and "patch",
unfortunately, would use the "diff -c" or "diff -u" line and try to patch
"dlnames.c" in the directory you're in, rather than in the "missing"
For "cvs diff -c" or "cvs diff -u" diffs, there's a Python script
"cvsdiff-fix.py" in the "tools" directory in the Wireshark source tree; it
will fix up those lines in "cvs diff" output. It reads its standard input
by default, or can be given a file name on the command line, and writes to
the standard output, so if you're typing at a command interpreter that
does piping, you could do something such as
python tools/cvsdiff.py patchfile | patch -p0 -
to use "patchfile". (You might be able to leave the "python" out of the
command line on many UN*Xes.)
"svn diff" doesn't produce a "diff -c" or "diff -u" line, so its output
doesn't have that problem. Regular "diff -c" or "diff -u" output also
shouldn't have that problem.