tools: explain reason for the explicit PerlIO load

Explain the reason for the explicit `use PerlIO::scalar;` statement
introduced in c4945bf ("tools: load PerlIO explicitly to avoid odd
failures")

Signed-off-by: Filip Schauer <f.schauer@proxmox.com>

src/PVE/Tools.pm

@@ -290,12 +290,12 @@ sub file_set_contents {
 	} else {
 	    # Encode wide characters with print before passing them to syswrite
 	    my $unencoded_data = $data;
-	    # Without this we get some "Can't locate PerlIO.pm in @INC" errors _sometimes_, and the
-	    # odd thing about it is that they can be "fixed" by calling file_set_contents in the
-	    # parent methode/code before the method, from another module, is called.
-	    # Anyway, loading PerlIO here should be fine as the in-memory variable writing is in
-	    # fact backed by the PerlIO based "scalar" module. This comment can be removed once the
-	    # odd behavior is really understood.
+	    # Preload PerlIO::scalar at compile time to prevent runtime loading issues when
+	    # file_set_contents is called with PVE::LXC::Setup::protected_call. Normally,
+	    # PerlIO::scalar is loaded implicitly during the execution of
+	    # `open(my $data_fh, '>', \$data)`. However, this fails if it is executed within a
+	    # chroot environment where the necessary PerlIO.pm module file is inaccessible.
+	    # Preloading the module ensures it is available regardless of the execution context.
 	    use PerlIO::scalar;
 	    open(my $data_fh, '>', \$data) or die "failed to open in-memory variable - $!\n";
 	    print $data_fh $unencoded_data;