April 14, 2008
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NOTE (December 2009): This bug has been fixed in Snow Leopard (10.6)
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Fixing Leopard Autofs for NIS Replicated Servers
Replicated servers are autofs map entries that list multiple locations
from which a resource can be mounted. These are some examples:
foo -ro,hard,intr host1:/path1/& host2:path2/& host3:path3/foo_orig
bar -ro,hard,intr host1,host2,host3:/path/&
baz -ro,hard,intr host1,host2:/path1/& host3:path3/baz_orig
When the automounter sees an entry like this and tires to mount it,
it's supposed to figure out which host is the "closest" and mount
from that one. If that host is unavailable, it tries the next
closest one. Furthermore, once filesystem is mounted, if the server
has a problem and goes offline, the kernel has a mechanism by which
it can fail over to another server, seamlessly.
[As of June '08 it's been reported to me (by an apparently reliable source)
that OS X does not support this failover, which isn't surprising
(I don't know of Linux versions that do either). But failing to failover
isn't a showstopper, just a nuisance.]
Under Leopard 10.5.1 and 10.5.2 (so far), this does not work. Fortunately,
Apple graciously
makes portions
of their code available,
including autofs,
so we were able to fix this problem. You'll need to become an Apple
Developer Connection member to download autofs, but this is free.
We downloaded the
autofs-109 tarball (you can also
browse
the files)
from under the
10.5.2 tree,
and our patches are based on this version.
(Note that the information below has been passed on to Apple, so
in theory a future release of OS X will not have these bugs!)
Fixing
What we found in the source code is that whoever wrote the replicated
server code was a bit confused about the difference between the
simple internet address format found in a hostent structure, and
the more complicated internet address information of a sockaddr
structure. We fixed two bugs springing from this misunderstanding,
one in nfs_cast.c, and one in autod_nfs.c. We have two patch
files available for patching these:
nfs_cast.patch and
autod_nfs.patch.
Apply these patches to the files in autofs-109/automountd/, and then
rebuild.
Building
You'll need to have Xcode installed on your Mac to build this.
autofs-109 does include autofs.xcode in the top directory that you
can use for the build, however
there are some outside components missing, so the build won't work
out of the box. There are several components missing, but you
don't have to build all of autofs; you'll only need to build a new
automountd (/usr/libexec/automountd), and for this you only need an
extra include file, mntopts.h, which can be found in another Apple
open source package, libutil (we used libutil-11 under 10.5.2 --
download tarball or
browse).
I'm not much of an Xcode guru, but by hacking and thrashing about a bit
I got it to compile. What I did is stick mntopts.h into the
autofs-109/header directory. Then I edited the files that used
to instead use "mntopts.h". This wasn't quite sufficient.
I also had to add this file to the project -- under Project menu, select
"Add to Project", and select this file.
The Xcode build still fails, but it gets past automountd, which is
successfully built. You can then copy it out of the build directory
(build/Development/automountd, in our case since we had it set up
for a Development build) and into /usr/libexec/automountd. I suggest
you save a copy of the original automountd in case something goes
horribly wrong.
Using
It's worked great for us so far. If you have replicated server entries
in your NIS maps, it should work for you too.
We haven't tested if there is any kind of failover [reportedly, no,
see
above], so for us that
remains to be seen. However getting the Leopard OS X to use our maps
in the general case has made it all worth while.
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