Hitchhiker's Guide to Openbsd

Applying patches.
Patches for the OpenBSD Operating System are distributed as "Unified diffs", which are text files that 
hold differences to the original source code. They are NOT distributed in binary form. This means that to 
apply a patch you must have the source code from the RELEASE version of your system available. In 
general, it is advisable to aquire the entire source tree before applying a patch. If you are running a release 
from an official CDROM, the source trees are available as files on disk 3, these can also be downloaded 
from the 
FTP servers
. We will assume you have the entire tree checked out. 
For our example here, we will look at patch 001 for OpenBSD 3.6 dealing with the 
st(4)
 driver, which 
handles tape drives. Without this patch, recovering data from backups was quite difficult. People using a 
tape drive needed this patch, however those without a tape drive may have had no particular need to install 
it. Let's look at the patch: 
# more 001_st.patch
Apply by doing:
cd /usr/src
patch -p0 < 001_st.patch
http://www.openbsd.org/faq/faq10.html (19 of 32)9/4/2011 10:02:15 AM

---

10 - System Management
Rebuild your kernel.
Index: sys/scsi/st.c
===================================================================
RCS file: /cvs/src/sys/scsi/st.c,v
retrieving revision 1.41
retrieving revision 1.41.2.1
diff -u -p -r1.41 -r1.41.2.1
--- sys/scsi/st.c 1 Aug 2004 23:01:06 -0000 1.41
+++ sys/scsi/st.c 2 Nov 2004 01:05:50 -0000
1.41.2.1
@@ -1815,7 +1815,7 @@ st_interpret_sense(xs)
u_int8_t skey = sense->flags & SSD_KEY;
int32_t info;
- if (((sense->flags & SDEV_OPEN) == 0) ||
+ if (((sc_link->flags & SDEV_OPEN) == 0) ||
(serr != 0x70 && serr != 0x71))
return (EJUSTRETURN); /* let the generic code 
handle it */
As you will note, the top of the patch includes brief instructions on applying it. We will assume you have 
put this patch into the 
/usr/src
directory, in which case, the following steps are used: 
# cd /usr/src
# patch -p0 < 001_st.patch
Hmm... Looks like a unified diff to me...
The text leading up to this was:
--------------------------
|Apply by doing:
| cd /usr/src
| patch -p0 < 001_st.patch
|
|Rebuild your kernel.
|
|Index: sys/scsi/st.c
|
===================================================================
|RCS file: /cvs/src/sys/scsi/st.c,v
|retrieving revision 1.41
|retrieving revision 1.41.2.1
|diff -u -p -r1.41 -r1.41.2.1
|--- sys/scsi/st.c 1 Aug 2004 23:01:06 -0000 1.41
|+++ sys/scsi/st.c 2 Nov 2004 01:05:50 -0000
http://www.openbsd.org/faq/faq10.html (20 of 32)9/4/2011 10:02:15 AM

---

10 - System Management
1.41.2.1
--------------------------
Patching file sys/scsi/st.c using Plan A...
Hunk #1 succeeded at 1815. <-- Look for this 
message!
done
Note the "
Hunk #1 succeeded
" message above. This indicates the patch was applied successfully. 
Many patches are more complex than this one, and will involve multiple hunks and multiple files, in 
which case, you should verify that all hunks succeeded on all files. If they did not, it normally means your 
source tree was different in some way from the release source tree the patch was created from, or you 
didn't follow instructions carefully, or your patch was mangled. Patches are very sensitive to "white space" 
-- copying and pasting from your browser will often change tab characters into spaces or otherwise alter 
the white space of a file, making it not apply. 
At this point, you can 
build and install
the new kernel, then reboot the system as normal. 
Not all patches are for the kernel. In some cases, you will have to rebuild individual utilities. At other 
times, will require recompiling all utilities statically linked to a patched library. Follow the guidance in the 
header of the patch, and if uncertain, rebuild the entire system. 
Patches that are irrelevant to your particular system need not be applied -- usually. For example, if you did 
not have a tape drive on your system, you would not benefit from the above patch. However, patches are 
assumed to be applied "in order" -- it is possible that a later patch is dependent upon an earlier one. Be 
aware of this if you elect to "pick and choose" which patches you apply, and if in doubt, apply them all, in 
order.