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Equinox/p2/Location selection scenarios
This page tries to collect scenarios and use cases for controlling the various locations used by p2. This includes managing the location initial location of a profile, p2's data area, shared locations, the location into which additional function is installed and the relationship to the bundle pool etc.
Each details a scenario and is followed by one or more approaches. In some cases the scenario is not currently supported and a bug report may be listed.
Select location on install
It should be possible to select the target location when installing plug-ins from within Eclipse. The functionality can be compared to selecting an extension location when installing plug-ins in the old Update Manager.
Remember the keynote at EclipseCon 2005? If you take control away from a user, it will make him/her unhappy. Some users are used to organize content on their systems the way they want to organize it. There are plenty reasons for this. For example, a user might want to place plug-ins from a single project into a separate folder - one folder containing the ECF, another containing Webtools. Later on he might want to share different folders between different runtime and development configurations.
Another user might want to organize plug-ins in a way he is used to. Maybe he just wants to align it better with the OS. But it is also possible that he simply wants to keep things separated (eg. don't mix experimental plug-ins from project XYZ with stable plug-ins from project ABC). Yet another option is to share some plug-ins between different runtime instances (eg. an image viewer plug-in and Subversion tooling for every instance but PDT only in one).
Therefore, a user should be able to keep control over the layout/organization of software on his computer and the p2 Update UI should assist him.
Another advantage are several usability improvements within Eclipse. The concept of extension locations has been well adopted within Eclipse. For example, PDE allows to select plug-ins in wizards, dialogs and editors by grouping them based on their install locations. This improves the usability in PDE when working with multiple Eclipse based applications/projects in multiple workspaces. For example, one can easily compose a target runtime simply by selecting the different plug-in locations - in one workspace it's Equinox + ECF in another it's the Platform + Webtools.
Mac OS X layout
The current Eclipse.app is pretty badly laid out for Mac OS X systems, as is the location of the bundles. Macs have several hierarchies of places where things can be expected to be placed/read from, in the following order:
- ~/Library/Application Support/Equinox/Bundles - accessible by the current user, probably read-write
- /Library/Application Support/Equinox/Bundles - shared across multiple users on the current computer, probably read-only
- /Network/Library/Application Support/Equinox/Bundles - shared across multiple computers, probably read-only
Although it should be possible to define these as 'dropins', there doesn't seem to be any easy/obvious way to have multiple such directories.
There's a bunch of secondary issues for the Mac bundle, such as that everything it needs should be inside the Eclipse.app rather than dropped outside it; and logs shouldn't be written inside, but rather outside in ~/Library/Logs. P2 is somewhat inflexible and assumes a wrietable location for the application isnatll folder when extracting e.g. configuration.ini. Even if that directory is writable (e.g. running with admin priviledges) it should defer to some per-user location instead. (The common argument - that we want to install multiple different versions of Eclipse - is almost completely unnecessary when running as a 'normal' user, but rather something that Eclipse developers might do more frequently.)
For a 'default' Eclipse install, it might make sense to have Eclipse.app/Contents/Resources/Equinox/Bundles/ as the location for key bundles, like ECF, OSGi.jar etc.
For people who use the Eclipse IDE for several different things, it has previously been possible to have several distinct installations of sharing *some* of their plugins.
The reason is that if you need very different functionality you do not want to clutter up your Eclipse install with everything.
For instance if you work with both Ruby and Java you might want one installation with a lot of Ruby specific plugins. But for Java you want a host of different plugins. Trying to mash it all into one install will likely generate a number of technical issues, and it will eat up a lot of RAM and become a whole lot slower.
But on the other hand you might need shared plugins like for SVN or basic technology plugins. And previously you could share those easily - along with the basic install - and only upgrade the shared stuff once. Now you have to maintain each installation separately and you waste a lot of hard disk space as well.
Even when the specific location of the shared stuff is not important, it is important to users to be able to define functional groups of plug-ins that can be installed/uninstalled as a group (Ruby stuff, Java stuff, etc.) And having downloaded these things before, a scripted/headless install is not enough. The user wants to know that these are kept locally. (See also Equinox_p2_UI_Use_Cases#Dave for a discussion of this requirement in terms of the p2 user persona, Dave).
Recovery from failures
Another thing that using Extension Locations gave me was that if the Eclipse install failed, for some reason, it would be easy to reinstall everything again. I have already once had a situation with Eclipse 3.4 where I simply couldn't update it anymore though P2 resulting in a complete reinstall of the entire thing. Before 3.4 I had all plugins - that was not part of the Eclipse distribution - in a number of Extension Locations. That made it easy to reinstall Eclipse as I would just unzip it again and point it at the Extension Locations I needed.
Similarly it was easy to remove a new plugin if I made sure to place it in a new Extension Location. I guess you could say I had a sort of quarantine Extension Location where I would place new stuff in. If they messed anything up I could easily get rid of them, even if the Update Manager wouldn't (I had cases of that, but to be fair not seen a similar situation in P2 yet)
Distribution in an restricted environment
We have to distribute an initial eclipse application with a defined set of bundles via an alternative software pooling mechanism, which is based on MSI technology. This mechanism installs software under a special account in the program files directory, where the user has no write permissions. If the user wants to install additional bundles we used the extension location and pointed to a directory where the user has write permissions. This directory must be set by the user, a predined directory (e.g.) the user's home directory is not applicable because of disc quota policies (only equinox.configuration.area is located in user's home). In general the user installs the additional plugins in D:\Data\[USERNAME] but not every user has a d-drive, so the location must be set by the user.