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RE: [eclipse-incubator-e4-dev] [resources] Alias management

Hi Terry,
after more investigations, I believe that we should make the following additions
to EFS:
  • String IFileStore#getCanonicalPath() throws CoreException
    Will be necessary for IWorkspace.findFilesForLocation() if a filesystem has symlinks.
    If we want to introduce this in a fully compatible fashion, we could also think about doing
  • Object IFileInfo#fileKey()
    A unique key identifying a file (e.g. on UNIX: Device ID + INode number), or null if not available.
    Can be used to determine with least effort whether two files are the same, e.g. in order to
    avoid cycles due to symbolic links when walking a file tree. I've had that idea for a very
    long time, and seeing it in JSR203 confirms for me that this is worthwhile.
  • boolean IFileStore#isSameFile(IFileStore other) throws CoreException
    Also for checking link cycles and fixing issues with case (in)sensitive file names.
    More efficient than doing getCanonicalPath() on both file stores... we might
    acutally get away without this API since it's only about efficiency.
  • boolean IFileInfo#getAttribute(EFS.ATTRIBUTE_SPECIAL_FILE)
    For files that are neither a directory nor regular file nor symbolic link (such as named
    pipes, Unix domain sockets, or devices). These should get special treatment.
  • boolean IFileStore#createSymbolicLink(String linkTarget, int options, IProgressMonitor mon) throws CoreException
    I think we need this for properly importing from file system / tar archive into workspace.
I'm not so sure any more if we really need more asynchronous support. What we might need,
though, is some API around manipulation of file system paths (resolving, concatenating, stripping)
as well as some Monitoring API.
> * IFileStore.isAlias() -- much lighter weight than getting the canonical path, only returns true if last segment is aliased
I think we have this already, with
   boolean IFileInfo#getAttribute(EFS.ATTRIBUTE_SYMLINK)
I'm not exactly sure how we could be dealing with hard links -- the fileKey() and
isSameFile() methods could help here, or we treat all kinds of aliases with
ATTRIBUTE_SYMLINK... I'm not sure. Hard links are also the same concept
as what McQ mentioned on system/i -- the very same file referenced in both
a case sensitive and case insensitive manner by different file paths.
I think that your other requirements are basically covered by
and the bugs referenced from there.
Martin Oberhuber, Senior Member of Technical Staff, Wind River
Target Management Project Lead, DSDP PMC Member

From: eclipse-incubator-e4-dev-bounces@xxxxxxxxxxx [mailto:eclipse-incubator-e4-dev-bounces@xxxxxxxxxxx] On Behalf Of Terry Parker
Sent: Wednesday, October 08, 2008 8:42 PM
To: E4 developer list
Subject: Re: [eclipse-incubator-e4-dev] [resources] Alias management

Hi Martin,

Thanks for your comments.  Keeping the file system layer stateless is the right approach.  I think the following additions would be sufficient:
* IFileStore.getCanonicalPath() 
* IFileStore.isAlias() -- much lighter weight than getting the canonical path, only returns true if last segment is aliased

A big concern I have is that if the resource layer solely adds getCanonicalPath() to existing methods, it won't get invoked consistently.  Perhaps having {IWorkspace,IProject}.findResource(String absolutePath) API calls as the primary/only way to convert a path string to a resource would provide the consistency we need.

Here are some scenarios for which we will want aliasing to work correctly:

A) The file "/real/" is symlinked by "/project_alias/".  Desired behavior:
* When a debugger returns the path "/real/", the debug framework opens the resource associated with project_alias, not a separate resource outside the workspace

B) "/project/external_lib/headers" is symlinked to the folder "/project/external_lib/v1234/src/headers".  "/project/external_lib/v1234/src/headers/file_with_syntax_error.h" fails to compile. Desired behavior:
* Clicking on a console hyperlink or a Problems pane item for the error opens the workspace-mapped resource.  (This is no different from A, but illustrates that symlinks can occur in any segment in a path, not just the end segment.)

C) "/project1/external_lib/headers" and "/project2/external_lib/headers" are both symlinked to the folder "/project1/external_lib/v1234/src/headers".  On a build of project1, code in an #ifdef in "/project/external_lib/v1234/src/headers/header.h" fails to compile. Desired behavior:
* You get two different editor panes when opening "/project1/external_lib/headers/header.h" and "/project1/external_lib/headers/header.h", since they may be used with different compilation directives, which would affect their display
* Clicking on a console hyperlink or a problems pane item for the error opens the workspace-mapped resource for the project1 version of the file
* Editing the "header.h" file updates both editors in concert


On Tue, Oct 7, 2008 at 10:31 AM, Oberhuber, Martin <Martin.Oberhuber@xxxxxxxxxxxxx> wrote:
Hi Terry,
I fully agree.
  1. Create / Modify Aliases. I also don't see a need for creating / modifying file system links from Eclipse. There should be support for visualizing them, though (which is easy to add in Eclipse 3.5 already).
  2. Consistent normalized path support. Agree. We'll need IFileStore#getCanonicalPath() on the EFS API, and we'll need smart algorithms on the Resource / Refresh / Compare code to avoid using getCanonicalPath() where possible, in order to maintain good performance. In other words, query the canonical path only when we come across an FS link, but construct the path ourselves for "regular" files and folders. The Workspace Tree will need some redesign to understand links "moving around" its structure.
  3. Serve up both normalized and non-normalized path strings. Yes, though I think this is probably more relevant for resource objects than for filesystem objects -- the FS layer does exactly that with a getCanonicalPath() API already, but since FS must be stateless it will be expensive. On the Resource layer, we can add state (caching) to make it faster.
    * the non-normalized path is how the client / user originally referred to a resource, and
    * the normalized path is its normalized variant (can be computed from the workspace tree).
  4. Support team providers for VCSs that can check in symlinks. I'm not sure if that is required. Assuming that foo/bar is a symlink, doing a "checkin foo/bar" will check in the symlink as needed. To me, it seems that all we need to make sure is that we don't instruct the VCS to check in the same file twice just because we approach a given (normalized) file through multiple different (non-normalized) paths. This should be possible through an improved alias-aware Workspace Tree.
I think that if we are careful, there is some potential to even add proper Alias Management in Eclipse 3.5 already, though that needs a lot more investigation. What I would propose, is starting that work soon in order to see whether we can apply it to Galileo already or whether it requires more radical change that would make it impossible in 3.5.
Martin Oberhuber, Senior Member of Technical Staff, Wind River
Target Management Project Lead, DSDP PMC Member

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