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Re: extattr namespaces

On Mon, Feb 06, 2012 at 05:04:45PM +0000, David Holland wrote:
> On Mon, Feb 06, 2012 at 09:51:19AM +0000, Emmanuel Dreyfus wrote:
>  > Here is public disuccsion about extended attributs namespaces, following
>  > a private request from yamt@
> Which of the two models does OS X use?

OS X doesn't directly support namespacing nor does it support a difference 
in access. If a file has an extended attribute, a program can read and 
write it.

Put another way, the whole API deals with "user" xattrs.

ls -l@ /

drwxr-xr-x@ 62 root  wheel         2108 Feb 17 20:48 sbin          32 

That's some of the output on my Lion system. Looking in ~/Downloads, we 
see some other interesting EAs:

-rw-r--r--@  1 wrstuden  staff     8381161 Apr  2  2010 things_1.3.3.dmg               20                80                53           166            74 

So just make the whole API do "user" and you're set.

The OS X file systems that have "system" EAs and which I am familiar with 
do not expose them using the normal EA APIs. HFS uses a special EA to 
store a file's ACL, and you never see it (nor should you).

Xsan supports user, system, and system.inherited EAs. Everything that 
comes from userland is a "user" EA. We use the "system" ones for Reverse 
Path data, so we can get a path for a file descriptor. The 
"system.inherited" ones are used by Quantum for their data migration work.

As above, just have the VFS layer handle "user" attributes. It's simpler 
and I don't think anything else will be reliable.

Take care,


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