Re: Can BTRFS handle XATTRs larger than 4K?

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2014-12-22 13:43, Chris Murphy wrote:
> On Mon, Dec 22, 2014 at 11:09 AM, Austin S Hemmelgarn
> <ahferroin7@gmail.com> wrote:
>
>> Personally, I'd love to see unlimited length xattr's like NTFS and HFS+ do,
>> as that would greatly improve interoperability (both Windows and OS X use
>> xattrs, although they call them 'alternative data streams' and 'forks'
>> respectively), and provide a higher likelihood that xattrs would start
>> getting used more.
>
> This is two years old, but it looks like NFS will not support xattr.
> http://comments.gmane.org/gmane.linux.nfs/53259
>
> It looks like SMB does support xattr (and sometimes requires it) but I
> have no idea to what degree, including the host/client preservation on
> different filesystems. [1] It would still be helpful for cp and rsync
> to be able to preserve xattr, however Apple has moved to a new on-disk
> format that makes the future of reading OS X volumes on Linux an open
> question. [2]
>
>
>
>
> [1]e.g. Btrfs > Samba- server > SMB over TCP > "Apple SMB2" > HFS+.
> And then the OS X client pushing a file to the server is a separate
> test. Next test would be OS X as server and Linux as client to do HFS+
>> "Apple SMB2" > SMB over TCP > Samba-client > Btrfs, and then Linux
> client pushing a file to OS X is a separate test. So it's four tests
> for any combination of filesystems.
>
> [2] Apple has a logical volume manager called CoreStorage. Until
> recently it's mainly used to implement full disk (volume) encryption,
> but encryption is actually optional. It's also used to combine SSD+HDD
> partitions into a single logical volume using the SSD as a cache.
> Starting with 10.10 "Yosemite" it's used by default for the main
> HFSJ/X volume for system/apps/user data, and even legacy OS X only
> installations are converted to a CoreStorage logical volume upon
> upgrading. There's no pre-baked support on linux for this right now,
> and I'm not really sure if/when we'd ever see this in a distribution
> by default.
> http://www.cl.cam.ac.uk/~osc22/docs/cl_fv2_presentation_2012.pdf
> https://github.com/libyal/libfvde/
>
>
I'm more thinking along the lines of not having to jump through hoops to 
get _ALL_ the data in a tar file from OS X to extract on a Linux box. 
Also, Windows has been using it's 'alternative data streams' 
functionality from NTFS more in recent years (the new 'file history' 
functionality in Win8/8.1 uses ADS for storing old copies of files), and 
these are essentially just forks with a extra compatibility interface. 
There are other potentially interesting uses though, for example, 
storing multiple localized versions of a text file as a single 
user-visible 'file'.


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