Hi all,
I had some thoughts about the Strawman proposal, and the file system
layer in particular.
*
We have a requirement to extend usability of Eclipse tools
beyond the Workspace. Bugs are open which request, for instance,
capabilities to Search files and folders outside the workspace, open
editors, add markers, ... apparently, we'll want to do all that on the
Filesystem layer.
*
Given that, the Filesystem layer must be stateless (we cannot
maintain state in memory for a tree that can become arbitrarily large,
since that wouldn't scale). The Filesystem layer must take its
information from the filesystem alone, and nowhere else. Which seems to
tie in nicely with ideas of having the FS layer RESTful.
*
If the Filesystem layer is stateless, we cannot push down any
resource deltas, since these require state ("before" vs "after" the
change). The Resources (Project) layer would remain the one which holds
state just as it does today.
*
I like the idea of pushing down metadata such that (a) markers
can live outside the workspace on FS objects, and (b) file system
capabilities for storing metadata such as Encoding or content type can
be leveraged. Perhaps that metadata layer could even be totally separate
from both FS Layer and Resource layer, linked with them through URI as
the identifier, and some resource delta callbacks for lifecycle
management. The other option is to leave it with the Resource layer, but
make it lazy (see below).
*
This brings up the question, where we really need to beef up the
FS layer? I actually don't see much need for this, except for
(a) adding asynchronous support if needed ... though that brings
up other questions (see my other E-Mail), and
(b) adding an IFileStore#getCanonicalPath() API which we clearly
need for Alias resolution.
*
I think that we can not have full Alias Management on the FS
Layer, because:
1.) one requirement of Alias management is that given some file
X, you need to know "who else links to X?".
2.) Now that kind of "reverse lookup" of symbolic links is not
supported by file systems, so it must be solved in code.
3.) That, again, requires that clients have "expressed
interest" in X before, which is adding state to the file system, which
we cannot have on the FS layer.
I think that we need to keep Alias Management on the
Resource/Project layer, supported by the getCanonicalPath() API on the
FS layer. In order to still support Alias Management for items outside
the workspace (that have been looked at before), we'll probably want
some "lazy addition to Workspace" paradigm which adds files and folders
to the workspace as they are being visited (and probably removes them
again after some time with an LRU paradigm).
Now that being said, it looks for me as if the necessary enhancements on
the FS layer could even be done in the Eclipse 3.5 Stream (adding
IFileStore#getCanonicalPath()).
Or am I missing any requirements on the FS Layer?
Cheers,
--
Martin Oberhuber, Senior Member of Technical Staff, Wind River
Target Management Project Lead, DSDP PMC Member
http://www.eclipse.org/dsdp/tm
.
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