[tahoe-dev] [tahoe-lafs] #845: "tahoe backup" and HFS+ OS-level immutable directories: copying Time Machine backups

[tahoe-lafs]

#845: "tahoe backup" and HFS+ OS-level immutable directories: copying Time
Machine backups
-------------------------------+--------------------------------------------
 Reporter:  warner             |           Owner:           
     Type:  enhancement        |          Status:  new      
 Priority:  major              |       Milestone:  undecided
Component:  code-frontend-cli  |         Version:  1.5.0    
 Keywords:                     |   Launchpad_bug:           
-------------------------------+--------------------------------------------
 Some local filesystems offer immutable directories (specifically HFS+, as
 created by apple's Time Machine backup tool). If the "tahoe backup"
 command were able to recognize these, it could run faster, by remembering
 that it had already made a copy of the local directory, and refraining
 from making a new copy each time.

 This probably requires a test like:

  * if local filesystem is HFS+, and
  * use some extended OS API calls to find out if the directory is
 immutable
  * then read devno and inodeno, then map into the dircache table of the
 backupdb

 We need to learn more about how immutable directories work on HFS+, to see
 what sorts of consistent identifiers can be used (I don't know if inodeno
 is appropriate, or even available).

 This would be useful to do e.g. "{{{tahoe backup /Volume
 /TMBackupDrive/Latest tahoe:somewhere}}}". When nothing had changed, the
 local disk IO would be reduced to a single directory read. (the current
 code would need to read the contents of every directory in the system,
 before being able to determine that the previously-uploaded directories
 could be re-used).

-- 
Ticket URL: <http://allmydata.org/trac/tahoe/ticket/845>
tahoe-lafs <http://allmydata.org>
secure decentralized file storage grid