Re: Support getrandom() for pg_strong_random() source

On Thu, Oct 23, 2025 at 2:48 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> I've drafted the patches for this item.

Thanks!

> The 0001 patch allows the packager to select the random source:
> "openssl" or "system", by using --with-random-source option. If it's
> omitted and OpenSSL is used (--with-openssl or --with-ssl=openssl),
> 'openssl' source is automatically chosen. The selected random source
> can be shown in read-only GUC parameter random_source.

I think 0001 is missing logic to switch pg_strong_random.c according
to the new #defines; selecting `system` still uses OpenSSL on my
machine.

> + --with-random-source=NAME
> + set random number source (system,openssl)

Bikeshedding: should we make it clear in the name that this covers
only the "strong" random implementation, for cryptography? Maybe
--with-strong-random, or --with-crypt-random, or...

> + AC_DEFINE([USE_RANDOM_SOURCE_OPENSSL] , 1, [Define to 1 to use OpenSSL libary for random number generation])

autoreconf 2.69 is refusing to process these AC_DEFINEs on my machine,
and I think it's because of the space between the end bracket ']' and
the comma. Removing it fixes generation for me.

> @@ -3500,5 +3507,4 @@
> options => 'io_method_options',
> assign_hook => 'assign_io_method',
> },
> -
> ]

(FWIW, I prefer the extra newline there; it's easier for me to read
and it matches the spacing at the top.)

> The 0002 patch supports getrandom() as a 'system' random source where
> available while keeping the method of reading /dev/urandom as a
> fallback option.

> +AC_CHECK_HEADER([sys/random.h],
> + [AC_CHECK_FUNCS([getrandom],
> + [AC_DEFINE(HAVE_GETRANDOM, 1, [Define to 1 if you have getrandom])])])

AC_CHECK_FUNCS([getrandom]) by itself should let autoconf take care of
the description; I think the extra AC_DEFINE there will duplicate some
handling.

> +if cc.has_header('sys/random.h') and cc.has_function('getrandom',
> + args: test_c_args, prefix: '''
> +#include <sys/random.h>''')
> + cdata.set('HAVE_GETRANDOM', 1)
> +endif

Some of the more complicated prefixes use multiline literals, but for
this case I think `prefix: '#include <sys/random.h'` would be more
readable. Also, is there a way to merge this check into the
check_funcs logic later on?

Thanks,
--Jacob