Fix compilation error on GNU Hurd architectures

[roehling]

The MAXTHREADNAMESIZE macro is not (yet?) defined for builds on GNU Hurd, so the ddsrt_thead_getname() function cannot rely on it.

[eboasson]

Thanks @roehling, the changes look fine to me, but I think it makes sense to wait until you tell me you have it building on GNU Hurd before merging this. Do you agree with that?

[roehling]

Yes, that is a good idea. The buildd for hurd-i386 seems quite busy at the moment, but I hope it will be done in a few hours. I'll let you know once it is done.

[roehling]

The build still fails on hurd-i386, and I don't have the time to hunt down the problem immediately, so I'll turn this into a draft and mark it ready for review once I sorted everything out.

[eboasson]

@roehling sounds good. I'm somewhat surprised it turns out to be so hard to build: I always thought we had managed to have a really small footprint in terms of OS-specific things. But it seems Hurd is making things more complicated ...

Feel free to share error messages if you think it useful.

[roehling]

The Hurd developers are very opinionated about the PATH_MAX macro, meaning they don't like it and do not provide it. I thought FILENAME_MAX was mandated by some standard, but apparently it does not work out-of-the-box. I need to check if I can fix it with a simple #include <stdio.h>, otherwise an arbitrary constant (such as the Linux value 1024) will have to do.

The Debian build logs are here in case you want to take a look for yourself: https://buildd.debian.org/status/package.php?p=cyclonedds

[roehling]

#include <stdio.h> has helped with FILENAME_MAX; but now I'm stuck on a different error:

/home/roehling/cyclonedds/src/core/ddsi/src/ddsi_udp.c: In function ‘joinleave_ssm_mcgroup’:
/home/roehling/cyclonedds/src/core/ddsi/src/ddsi_udp.c:649:57: error: ‘MCAST_JOIN_SOURCE_GROUP’ undeclared (first use in this function)
  649 |     rc = ddsrt_setsockopt (socket, IPPROTO_IPV6, join ? MCAST_JOIN_SOURCE_GROUP : MCAST_LEAVE_SOURCE_GROUP, &gsr, sizeof (gsr));
      |                                                         ^~~~~~~~~~~~~~~~~~~~~~~
/home/roehling/cyclonedds/src/core/ddsi/src/ddsi_udp.c:649:57: note: each undeclared identifier is reported only once for each function it appears in
/home/roehling/cyclonedds/src/core/ddsi/src/ddsi_udp.c:649:83: error: ‘MCAST_LEAVE_SOURCE_GROUP’ undeclared (first use in this function)
  649 |     rc = ddsrt_setsockopt (socket, IPPROTO_IPV6, join ? MCAST_JOIN_SOURCE_GROUP : MCAST_LEAVE_SOURCE_GROUP, &gsr, sizeof (gsr));
      |                                                                                   ^~~~~~~~~~~~~~~~~~~~~~~~
/home/roehling/cyclonedds/src/core/ddsi/src/ddsi_udp.c:662:55: error: ‘IP_ADD_SOURCE_MEMBERSHIP’ undeclared (first use in this function); did you mean ‘IP_ADD_MEMBERSHIP’?
  662 |     rc = ddsrt_setsockopt (socket, IPPROTO_IP, join ? IP_ADD_SOURCE_MEMBERSHIP : IP_DROP_SOURCE_MEMBERSHIP, &mreq, sizeof (mreq));
      |                                                       ^~~~~~~~~~~~~~~~~~~~~~~~
      |                                                       IP_ADD_MEMBERSHIP
/home/roehling/cyclonedds/src/core/ddsi/src/ddsi_udp.c:662:82: error: ‘IP_DROP_SOURCE_MEMBERSHIP’ undeclared (first use in this function); did you mean ‘IP_DROP_MEMBERSHIP’?
  662 |     rc = ddsrt_setsockopt (socket, IPPROTO_IP, join ? IP_ADD_SOURCE_MEMBERSHIP : IP_DROP_SOURCE_MEMBERSHIP, &mreq, sizeof (mreq));
      |                                                                                  ^~~~~~~~~~~~~~~~~~~~~~~~~
      |                                                                                  IP_DROP_MEMBERSHIP
src/core/CMakeFiles/ddsc.dir/build.make:138: recipe for target 'src/core/CMakeFiles/ddsc.dir/ddsi/src/ddsi_udp.c.o' failed

I did a bit of superficial googling, but I could not come up with an obvious fix, and I could not find the missing identifiers by grepping /usr/include on a GNU Hurd machine.

[thijsmie]

Hey @roehling, Just pinging you while I clean out the dust from the PR closet. Fixing builds for specific architectures is always nice, so if it is still relevant I'd like to get it to work. Since I (and probably all others working daily on CycloneDDS) do not have access to a GNU Hurd machine it is up to you to close this or ready the PR.

[roehling]

I haven't checked on this in a while, but as it turns out, Debian GNU Hurd has had a libc update that added the missing multicast macro definitions, so the PR builds just fine on hurd-i386 now. Feel free to merge.

EDIT As it actually turns out, setting -DENABLE_SOURCE_SPECIFIC_MULTICAST=OFF in combination with the PR fixes the build on GNU Hurd.

[thijsmie]

Just re-ran the test (shame they ran with the old pipeline definitions but okay https://dev.azure.com/eclipse-cyclonedds/cyclonedds/_build/results?buildId=3430&view=results) and everything seems fine. I'll merge this now! @roehling you could contribute a guide to docs/dev/gnu-hurd.rst similar to docs/dev/freertos.md with build instructions if you feel like it is warranted.