On 5/6/21 9:55 AM, Andrew Dunstan wrote:
> On 5/6/21 12:59 AM, Andres Freund wrote:
>> Hi,
>>
>> On 2021-05-06 00:18:12 -0400, Tom Lane wrote:
>>> Andres Freund <and...@anarazel.de> writes:
>>>> I understand why we don't want to rely on sed because of windows - but
>>>> it's far from obvious why we can't just use the .pl variant all the
>>>> time?
>>> Perl is not considered a hard build requirement on non-Windows.
>> Oops, forgot that.
>>
>>
>>> We could dodge that by shipping a pre-built dummy probes.h,
>>> but that doesn't really seem like a cleaner way than what's
>>> there now.
>> I tried to regenerate Gen_dummy_probes.pl using s2p - which doesn't seem
>> to exist for modern versions of perl anymore :(
>>
>>
>>> Also, as I read it, Gen_dummy_probes.sed is useful in any case as
>>> being the "source code" for Gen_dummy_probes.pl. You'd need some
>>> other form of documentation if you removed it.
>
> I suggest we add a README that sets out
>
>
> a) why we do things this way
>
> b) that the sed script is what's authoritative
>
> c) how to regenerate the perl script if you change the sed script,
> including where to get s2p
>
>
> I can do that.
>
>
Here's a patch that adds the README and also adds a Makefile recipe for
regenerating Gen_dummy_probes.pl after the sed script is changed. On my
system at least the recipe is idempotent.
cheers
andrew
--
Andrew Dunstan
EDB: https://www.enterprisedb.com
>From 488d812f06fe9ebe53368228af78e7ec8d7478d5 Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <and...@dunslane.net>
Date: Fri, 7 May 2021 10:08:01 -0400
Subject: [PATCH] Add a README and Makefile recipe for Gen_dummy_probes.pl
---
src/backend/utils/Makefile | 10 +++++++++
src/backend/utils/README.Gen_dummy_probes | 25 +++++++++++++++++++++++
2 files changed, 35 insertions(+)
create mode 100644 src/backend/utils/README.Gen_dummy_probes
diff --git a/src/backend/utils/Makefile b/src/backend/utils/Makefile
index 59b2255260..bcf9dd41ad 100644
--- a/src/backend/utils/Makefile
+++ b/src/backend/utils/Makefile
@@ -88,6 +88,16 @@ $(top_builddir)/src/include/utils/probes.h: probes.h
cd '$(dir $@)' && rm -f $(notdir $@) && \
$(LN_S) "../../../$(subdir)/probes.h" .
+# Recipe for rebuilding the Perl version of Gen_dummy_probes
+# Nothing depends on it, so it will never be called unless explicitly requested
+# The last two lines of the recipe format the script according to our
+# standard and put back some blank lines for improved readability.
+Gen_dummy_probes.pl: Gen_dummy_probes.sed
+ perl -ni -e ' print; exit if /^\$$0/;' $@
+ s2p -f $< | sed -e 1,4d -e '/# #/d' -e '$$d' >> $@
+ perltidy --profile=../../tools/pgindent/perltidyrc $@
+ perl -pi -e '!$$lb && ( /^\t+#/ || /^# prototypes/ ) && print qq{\n};'\
+ -e '$$lb = m/^\n/; ' $@
.PHONY: install-data
install-data: errcodes.txt installdirs
diff --git a/src/backend/utils/README.Gen_dummy_probes b/src/backend/utils/README.Gen_dummy_probes
new file mode 100644
index 0000000000..90fec37bce
--- /dev/null
+++ b/src/backend/utils/README.Gen_dummy_probes
@@ -0,0 +1,25 @@
+# Generating dummy probes
+
+If Postgres isn't configured with dtrace enabled, we need to generate
+dummy probes for the entries in probes.d, that do nothing.
+
+This is accomplished in Unix via the sed script `Gen_dummy_probes.sed`. We
+used to use this in MSVC builds using the perl utility `psed`, which mimicked
+sed. However, that utility disappeared from Windows perl distributions and so
+we converted the sed script to a perl script to be used in MSVC builds.
+
+We still keep the sed script as the authoritative source for generating
+these dummy probes because except on Windows perl is not a hard requirement
+when building from a tarball.
+
+So, if you need to change the way dummy probes are generated, first change
+the sed script, and when it's working generate the perl script. This can
+be accomplished by using the perl utility s2p.
+
+s2p is no longer part of the perl core, so it might not be on your system,
+but it is available on CPAN and also in many package systems. e.g.
+on Fedora it can be installed using `cpan App::s2p` or
+`dnf install perl-App-s2p`.
+
+The Makefile contains a recipe for regenerating Gen_dummy_probes.pl, so all
+you need to do is once you have s2p installed is `make Gen_dummy_probes.pl`
--
2.25.4
