Extended attributes in MacOS X

[Wesley W. Terpstra]

On Oct 25, 2006, at 9:10 PM, Wesley W. Terpstra wrote:
>> As for prefixing all MacOS xattrs with "user.", we'd need to come up
>> with some rules that would preserve the xattrs for all data paths:
>> Mac -> Mac, Mac -> Posix -> Mac, and Posix -> Mac -> Posix.  So, a  
>> Mac
>> receiver would need to be able to differentiate what entries  
>> needed the
>> extra prefix stripped, and which did not.  So, perhaps adding  
>> something
>> like "user.N0nP0s1%." to any non "user." data (that's NonPosix  
>> spelled
>> with 2 zeros, a one, and a percent).  That would make the stripping
>> rule pretty straight forward on the Mac side.
>
> I just don't know enough about these issues to have an opinion;  
> that's why I asked here

I will add this:
com.apple.ResourceFork
	is used by MacOS internally to expose/modify the resource fork
com.apple.FinderInfo
	is used by the Finder to track stuff like icon/program to open with/etc
com.apple.acl.text
	is used when a file with an ACL is copied to a non-HFS volume.  
However, this seems to be broken, because if you copy the file back,  
the EA remains and the ACL is not restored. I suspect this is  
probably some bug in osx that will be fixed in the future, though. It  
is NOT set when the file has working ACLs on the local volume.

The namespace appears to be flat aside from this, allowing EAs of any  
shape and size. Even 'system.x' seems to be allowed, despite an  
article I read claiming this was reserved.