Horton

Re: Cleaning up historical portability baggage

Michael Banck <mbanck@gmx.net>

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From: Michael Banck <mbanck@gmx.net>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Andrew Dunstan <andrew@dunslane.net>, Robert Haas <robertmhaas@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-06-10T10:59:16Z
Lists: pgsql-hackers 
Hi,

On Tue, Jun 10, 2025 at 09:05:03AM +1200, Thomas Munro wrote:
> On Tue, Jun 10, 2025 at 2:25 AM Andres Freund <andres@anarazel.de> wrote:
> > On 2025-06-09 15:25:22 +0200, Michael Banck wrote:
> > > Postgres built fine up and until v15 on the Hurd, so this is a build
> > > regression, and the fact that we define #PG_IOV_MAX to at most 32
> > > anyway suggest we could just #definde IOV_MAX to 16 if undefined as on
> > > Windows.
> >
> > I think our policy basically is that if it doesn't exist on the BF, it's
> > unsupported. Also note that Hurd is not listed as a supported OS:
> > https://www.postgresql.org/docs/devel/supported-platforms.html
> >
> > We can't design for OS that we don't know it's used with postgres and/or how
> > that OS works / what it supports.
> >
> > So I reject the premise that this is a regression.
> >
> > If you want to argue that we should add support for Hurd, you can do that, but
> > that's obviously a different discussion.
> 
> Since time immemorial, PostgreSQL could compile successfully on
> GNU/Hurd systems (perhaps with a few superficial tweak patches of this
> ilk), but it couldn't actually run because its semaphores didn't work
> cross-process.  I knew that because Christoph told us somewhere on
> this list not so long ago, but it seems there has been some movement
> since then and I am guilty of being wrong on the internet, as
> mentioned here:
> 
> https://savannah.gnu.org/task/?7050

Yeah.
 
> So it looks like they added working semaphores in 2022, but in 2023 I
> removed some unrelated stuff during and happened to mention that Hurd
> can't run PostgreSQL anyway, and they didn't like that (I mean it
> wasn't an unreasonable chain of thought, it was just unfortunate
> timing given they'd worked on addressing that).  The log linked there
> shows the regression tests mostly passing, so that seems promising: at
> least a cluster can finally actually start up and run!  There may be a
> few more little things to chase down, who knows.

I tried again (as seen in this thread) and the current status is:

1. build failure due to IOV_MAX being undefined (under discussion here)
2. initdb (at least) fails with assert-enabled builds due to O_RDONLY
being 1 on the Hurd and 0 everywhere else, I sent a patch for that here:
https://www.postgresql.org/message-id/68480868.5d0a0220.1e214d.68a6%40mx.google.com
3. make check nowadays succeeds the subscription test that it failed in
the log mentioned in the above task, but it still fails the stats test:

|@@ -672,7 +672,7 @@
| SELECT stats_reset > :'slru_commit_ts_reset_ts'::timestamptz FROM pg_stat_slru WHERE name = 'CommitTs';
|  ?column? 
| ----------
|- t
|+ f
| (1 row)
| 
| SELECT stats_reset > :'slru_notify_reset_ts'::timestamptz FROM pg_stat_slru WHERE name = 'Notify';
|@@ -769,7 +769,7 @@
| SELECT stats_reset > :'db_reset_ts'::timestamptz FROM pg_stat_database WHERE datname = (SELECT current_database());
|  ?column? 
| ----------
|- t
|+ f
| (1 row)
| 
| ----

I'll try to figure out why that is next.

> I wonder if the pthreads implementation is still unfinished as hinted
> at there too.

I think it is reasonably complete nowadays that I don't think it makes
sense to worry about this right now.

> Anyway, that's a long way of saying +1, GNU/Hurd would be a new
> platform for us, and obviously it hasn't even been plausible until
> quite recently.  There are also circularities when you're bringing up
> an OS and application support for it in parallel, so there will no
> doubt be a few little threads like this along the way, and I'm not
> against helping on our side.  More than that, for the specific point,
> yeah the GNU project's unlimited limits thing is kinda admirable, and
> they are quite right to complain about this one: {IOV_MAX} appears
> with curly braces in POSIX and <limits.h> says:
> 
> "A definition of one of the symbolic constants in the following list
> shall be omitted from <limits.h> on specific implementations where the
> corresponding value is equal to or greater than the stated minimum,
> but is unspecified."
> 
> So irrespective of Hurd support, it was a mistake to require the
> symbol to be defined, based on POSIX language lawyering alone.  It's
> annoying though, we've hit the only known system so far that doesn't
> actually define it, and POSIX then says we can only rely on 16 if we
> want a compile-time limit.  Yet Hurd presumably really wants to make
> it unlimited (well limited only by things like data types), while
> POSIX says that if we want to use anything but the required minimum
> when the macro isn't defined, we should call sysconf(_SC_IOV_MAX) at
> runtime.  So... I guess the correct thing to do may be to use 16 for
> the benefit of our (few) statically sized arrays that Richard Stallman
> would hate, but also consult sysconf() when limiting
> io_max_combine_limit, our own runtime bound on I/O combining for the
> main serious user of vectored I/O.  A little complicated, but...
> they're quite right about all that.  Hnghh.

I don't have an opinion here, I think it would be ok to just define it
to 16 if it is undefined and if the Hurd people want something better at
some point, they should submit patches.


Michael

Commits

  1. Make sure IOV_MAX is defined.

  2. Doc: Abstract AF_UNIX sockets don't work on Windows.

  3. Clean up inconsistent use of fflush().

  4. Remove configure probe for sockaddr_in6 and require AF_INET6.

  5. Remove configure probes for sockaddr_storage members.

  6. Remove configure probe for netinet/tcp.h.

  7. Fix macro problem with gai_strerror on Windows.

  8. Remove configure probe for net/if.h.

  9. mstcpip.h is not missing on MinGW.

  10. Remove dead ifaddr.c fallback code.

  11. Remove configure probe for gethostbyname_r.

  12. Remove replacement code for getaddrinfo.

  13. Remove configure probe for struct sockaddr_storage.

  14. Remove HAVE_UNIX_SOCKETS.

  15. Remove configurability of PPC spinlock assembly code.

  16. Remove configure probe for shl_load library.

  17. Remove configure probe for sys/select.h.

  18. Remove configure probes for sys/un.h and struct sockaddr_un.

  19. Remove configure probes for sys/ipc.h, sys/sem.h, sys/shm.h.

  20. Remove configure probe for sys/resource.h and refactor.

  21. Remove configure probe for sys/uio.h.

  22. Fix obsolete comments in instr_time.h.

  23. aix: fix misreading of condition in 8f12a4e7add

  24. aix: Remove checks for very old OS versions

  25. windows: Remove HAVE_MINIDUMP_TYPE test

  26. solaris: Remove unnecessary gcc / gnu ld vs sun studio differences

  27. Trust a few system headers to stand on their own

  28. Rely on __func__ being supported

  29. Simplify replacement code for strtof.

  30. Simplify gettimeofday for Windows.

  31. Simplify gettimeofday() fallback logic.

  32. Remove fallbacks for strtoll, strtoull.

  33. Remove configure probe for fdatasync.

  34. Remove configure probe for clock_gettime.

  35. Simplify replacement code for preadv and pwritev.

  36. Remove dead pread and pwrite replacement code.

  37. Remove dead setenv, unsetenv replacement code.

  38. Remove configure probes for poll and poll.h.

  39. Remove configure probe for link.

  40. Remove configure probes for symlink/readlink, and dead code.

  41. Remove configure probe for setsid.

  42. Remove configure probe for shm_open.

  43. Remove configure probe and related tests for getrlimit.

  44. Remove configure probe for dlopen, and refactor.

  45. Remove dead getpwuid_r replacement code.

  46. Remove dead handling for pre-POSIX sigwait().

  47. Remove dead getrusage replacement code.

  48. Cygwin and Mingw floating-point fixes.

  49. Support platforms where strtoll/strtoull are spelled __strtoll/__strtoull.

  50. Arrange to supply declarations for strtoll/strtoull if needed.

  51. Lock down regression testing temporary clusters on Windows.

  52. Secure Unix-domain sockets of "make check" temporary clusters.

  53. Add configure checks for strtoll, strtoull (or strto[u]q). Disable

  54. Portability fix for old SunOS releases: fflush(NULL)