Preserve xattr by default?

[Vassilis Palassopoulos]

xattr seems to becoming more useful everyday as it's being used by more applications to store data on them, for example for tagging purposes. This is a good reason to have future versions of BIT preserve xattr by default.

Here is a list of examples that use xattr to store tags:

- KDE 4.13 http://vhanda.in/blog/2014/07/tagging-your-files/

- OS X 10.9 http://arstechnica.com/apple/2013/10/os-x-10-9/9/

Of course preserving xattr by default would be problematic in cases where the filesystem wouldn't support them

With a preliminary check on wikipedia, one can see that there is xattr support in the following cases

Linux: ext2, ext3, ext4, JFS, Squashfs, ReiserFS, XFS, Btrfs and OCFS2 1.6

OS X: HFS+ since 10.4 (since 10.6 Cocoa applications don't preserve xattr on save e.g. TextEdit, Preview)

Windows: FAT, HPFS, and NTFS (limited support I think)

https://en.wikipedia.org/wiki/Extended_file_attributes

Additionally NFS doesn't support xattr nor has any plans to do so according to a mailing list I found where the devs were against it: http://comments.gmane.org/gmane.linux.nfs/53259

A notable case worth mentioning is GNOME Tracker which doesn't use xattr to store tags (it stores them only in the database used for indexing and querying with the exception of special cases like images where it uses EXIF tags alongside the database). I had a chat on IRC with martyn, the main dev of the project and he told me that he didn't like it that way and that he would prefer if in the future Tracker would also store tags in xattr in addition to the database.

Finally there have been reported cases of problematic support of xattr one should be aware of and were solved in the past by adding the option to enable/disable it:

https://bugs.launchpad.net/backintime/+bug/571894
https://bugs.launchpad.net/backintime/+bug/489380

[Germar (germar)]

There should be a check if destination FS supports acl and xattr and warn/deactivate the option in that case.