Have 'make uninstall' delete plugins which are no longer built

[SteveErl]

This update modifies the uninstall rule in mythplugins/cleanup/Makefile to delete plugins which are not being built. If a builder reruns configuration to eliminate a plugin which was previously included, but fails to run uninstall before doing so, the old plugin may be left behind. Running make uninstall after the configuration changes wouldn't work. These changes will remove plugins which are no longer configured to be built.

Resolves #1174

Checklist

• contribution does not duplicate one of our existing pull requests
• contribution is in a branch rebased against master
• code compiles successfully without errors
• code follows the MythTV Coding Standards
• documentation added/updated/removed where necessary
• commits are logically organised and have good commit messages

[linuxdude42]

This does not belong in a "make install" command. I have no objection to it being part of a "make uninstall" command.

[kmdewaal]

As I understand it this patch does remove the old plugins when there is a new plugin built.
But you can have an old build with more plugins than the new build and then there will be one or more old plugins still remaining, which can then cause a crash.
This is another reason to put this functionality in a "make uninstall" and I assume it can then uninstall everything that was previously installed.

[SteveErl]

I could try moving it to make uninstall, but then it will only work if builders know that there is this sneaky hidden problem and that they need to run make uninstall to fix it. Do you always run make uninstall before running make install in the plugins directory? I haven't been doing that. I just tried it out to see how well it works. The output is a bit scary.

It tries, but luckily fails to remove /usr/bin/, /usr/share/mythtv/, /usr/share/mythtv/bindings, /usr/share/mythtv/fonts, /usr/share/mythtv/locales, /usr/share/mythtv/metadata, /usr/share/mythtv/mythconverg_backup.pl, /usr/share/mythtv/mythconverg_restore.pl, /usr/share/mythtv/sql, /usr/share/mythtv/themes. None of these are parts of the plugins. They are components of the mythbackend, mythfrontend, or the operating system.

I prefer to consider sudo make install a request to make sure the plugins currently being built are the only ones to be loaded by mythfrontend.

[kmdewaal]

A few comments.

• I think this is more a package management problem. It should be possible to build a package and then install that package. I think that some users do actually do this. This then solves the problem of removing the old package.
• For my development I do use "make install" but I use dedicated target directories. Afte rmajor changes I just remove the complete target directory (e.g. /home/klaas/mythtv-master/usr/...) before doing the make install.
• A proper solution would be that mythfrontend does do a better job of checking the version of the plugin before loading it. There some form of checking, as loading plugins sometimes fails with a version number mismatch message, but it also sometimes crashes. Maybe this check can be improved.

[SteveErl]

The way the version check is currently implemented is that the plugin detects that its version does not match the libmythbase version. But this check is only done once the plugin is loaded, and by then, it's too late to avoid the memory corruption.

I looked into ways to implement your suggested "proper solution". The only way I found was

$ strings /usr/lib/mythtv/plugins/libmythmusic.so | grep libmythbase- | sed 's/^.*\.so\.//'
37
$ strings /usr/lib/mythtv/plugins/libmythweather.so | grep libmythbase- | sed 's/^.*\.so\.//'
34

This could work on Linux and MacOS, but Windows does not have a direct built-in equivalent that extracts strings from binary files in the same way the Linux strings command does. It also doesn't have a direct built-in equivalent to sed.

Implementing your "proper solution" would be quite complicated. The solution I came up with in this Pull Request is tremendously more simple. It will throw out libmythweather.so on my system since that plugin is expecting an old libmythbase version (34). As a result, it will never get loaded, and we avoid the memory corruption. The builder doesn't need to know about a new requirement that they run sudo make uninstall before sudo make install.

I grant that it's unusual to delete something during a make install command, but it's the simplest, most elegant solution to this problem.

[SteveErl]

I've moved the cleanup of old plugins from the install rule to the uninstall rule.