set_rcvar() function use?

[Hiroki Sato]

Pavel Timofeev <timp87 at gmail.com> wrote
  in <CAAoTqfss_-=N4EGd=XKDA+tzqvK5YZ7Ci6QJZvvip2xc64fYrw at mail.gmail.com>:

ti> Hello, dear community. I'm confused, please, help me.
ti>
ti> There is a rc.subr function which was buried[1] and resurrected[2] after a
ti> couple of years in almost the same form.
ti>
ti> I don't know what happened behind the scenes, but I have a question.
ti> Is it a preferable way to define a rc.conf variable these days in rc
ti> scripts (again/over and over)?

 I resurrected it because I wanted to change the standard style to use
 set_rcvar() to declare the user-configurable variables, their default
 values, and descriptions without losing backward compatibility.
 There is no clear consensus on this migration, however.

 The primary motivation was to add multi-instance support in rc
 scrupts[1].  To support this, the set_rcvar() style was required.

 [1] https://lists.freebsd.org/pipermail/freebsd-current/2014-October/052706.html

 Another issue I am aware of is that rc scripts installed by ports/pkg
 that they cannot have related entries in /etc/defaults/rc.conf for
 the default values.  So a lot of ports tend to end up with
 assignments in the rc scripts like this:

 : ${foo_enable=YES}

 This introduces inconsistency and it is difficult to find
 documentation about which knobs are available.  The set_rcvar() style
 should mitigate this and also implements a support to obsolete a
 variable when needed.  set_rcvar_obsolete() will convert the old
 value to the new variable automatically or emit an error if there is
 no compatibility between the old and the new.

 I committed set_rcvar() part only in [1], not whole of the
 multi-instance support.  This is because it was quite difficult to
 control which version of rc.subr is installed.  If rc scipts in ports
 use set_rcvar() on older versions of FreeBSD which do not support it,
 the port breaks.  At this moment all of the supported FreeBSD
 versions have the resurrected set_rcvar(), so I think it is now safe
 to use it globally.  Probably we might want to add a version number
 or feature flags in rc.subr to prevent this kind of situation.

 I am planning to revisit the multi-instance support shortly because I
 am using it for a long time and I think it is useful.  While I did
 not receive a strong objection to it so far, it is also true that
 adopting the set_rcvar() style was not discussed properly.  I would
 like more feedback before moving forward.

-- Hiroki
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