[Unison-hackers] Unison on a Synology DS412+

[Fabrice Rossi]

Hi,

A short digression before the real subject: a huge thanks to all the
unison developers for probably the most reliable software I've being using.

As unison fits (almost) perfectly my needs for file synchronization,
I've being trying to use it on my brand new nas, a Synology DS412+. I've
experienced minor difficulties trying to compile and one part of the
solution should probably be included into the sources, if I'm not
mistaken. I include below a full description, hoping this might provide
a good reference. All of this is tested with the current svn (revision
525, unison 2.46.20).

1) inotify
As you might know, Synology's Nas are linux computers, but with some
rather conservative versions of many things. In particular, they use the
glibc 2.3.6 on the DS412+ (even with the brand new system!), which is a
bit disturbing (and very very old). An annoying aspect of this version
is that it does not include inotify support (it started in 2.4). As I'm
very happy with unison 2.46.20 from the svn with the fsmonitor on my
linux boxes, I really wanted to have inotify support.

Unison sources include a work around for glibc prior 2.4 as
fsmonitor/linux/inotify_stubs.c reads:
#if __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 4
#define GLIBC_SUPPORT_INOTIFY 1
#else
#define GLIBC_SUPPORT_INOTIFY 0
#endif

#if GLIBC_SUPPORT_INOTIFY
#include <sys/inotify.h>
#else
#include "inotify_compat.h"
#endif

Unfortunately, inotify-compat.h is not included in the svn repository.
I've found a similar file in the ocaml-inotify repository
https://github.com/vincenthz/ocaml-inotify, but for some reason, it does
not compile on the DS412+. Probably a too old version of something. I
was however successful with a comparable header from inotify-tools,
here:
https://github.com/rvoicilas/inotify-tools/blob/master/libinotifytools/src/inotifytools/inotify-nosys.h.
So I would recommend to add to the svn repository something similar to
this old glibc workaround.

2) native code
With this file, unison compiles correctly, but in bytecode only as the
ocaml compiler from the ipkg repository does not include ocamlopt.
Recompiling a recent version of ocaml directly on the nas solves the
problem but one has to specify manually a 32 bits architecture as the
configure script seems to be confused by the peculiar Synology
organization. So I had to use for ocaml 4.01:
./configure -cc "gcc -m32" -as "as --32" -aspp "gcc -m32 -c"
-host i386-linux -partialld "ld -r -melf_i386" -prefix /opt
prior
make world.opt
There are probably better options, but the default ones figured out by
./configure with a amd64 architecture does not work (the CPU is an Intel
Atom D2701, so I'm puzzled).

Anyway, after this build, make UISTYLE=text works perfectly, except some
final errors related to etags (as I've not emacs installed on the nas,
as far as I understand).

3) selftest
A final note: while the obtained binary seems to work, selftest does
not. More precisely, I've got:
nas> ./unison -selftest
Contacting server...
Running internal tests...
fastercheckUNSAFE 1...
Test fastercheckUNSAFE 1 / 3b:
Expected R2 =
  Dir [("x", File "f00")]
but found
  Dir [("x", File "bar")]

Fatal error: Self-test fastercheckUNSAFE 1 / 3b failed!

Disturbingly, I've got the very same error on a standard ubuntu 12.04
box (here this is with ocaml 3.12.1). I'm probably doing something wrong.


So if you set aside this selftest issue, everything seems to work
perfectly. In particular, the fsmonitor works as expected, which is
really great. I've not made any intensive tests, as I would like to have
the opinion of the experts from this list on two things. Firstly is the
inotify header I've been using a good solution? Secondly, what about
this broken selftest on a perfectly standard ubuntu distro?

Thanks in advance,

Best,

Fabrice

PS: my caml knowledge is close to zero, by the way :-(