{"id":26045,"date":"2019-07-23T16:41:49","date_gmt":"2019-07-23T20:41:49","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=26045"},"modified":"2019-12-19T14:57:15","modified_gmt":"2019-12-19T19:57:15","slug":"xattr-flags-and-icloud-drive","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2019\/07\/23\/xattr-flags-and-icloud-drive\/","title":{"rendered":"xattr Flags and iCloud Drive"},"content":{"rendered":"

Howard Oakley<\/a>:<\/p>\n

\n

If you work with xattrs, you’ve probably already seen this in xattrs whose name ends with a hash # then one or more characters: that’s actually the flags, not part of the name, what Apple refers to as a ‘property list’. To avoid confusion I won’t use that term here, but refer to them as xattr flags. A common example of this is com.apple.lastuseddate#PS<\/code>, which is seen quite widely.<\/p>\n

Flags can be upper or lower case letters C, N, P and S, and invariably follow the # separator, which is presumably otherwise forbidden from use in a xattr’s name. Upper case sets (enables) that property, whilst lower case clears (disables) that property.<\/p>\n

[…]<\/p>\n

The sought-for ‘whitelist’ is actually baked into the xattr flag code, where as of 2013 the following default flags are set for different types of xattr[…]<\/p>\n

[…]<\/p>\n

If you want a xattr preserved when it passes through iCloud, you therefore need to give it a name which ends in the xattr flag S<\/strong>, such as co.eclecticlight.MyTest#S<\/code>.<\/p>\n<\/blockquote>\n

This is like filename extensions all over again, cramming two pieces of data into the same field. If you have an app that uses xattrs (maybe even from before iCloud Drive was introduced), you need to migrate all your metadata (and forever check the old xattrs when reading a file) if you want to set the “flags” for proper iCloud treatment.<\/p>\n\n

Previously:<\/p>\n