[tahoe-dev] Tahoe Lock Files again

[zooko]

Folks:

Brian's observation that K == 1 makes directories susceptible to  
rollback [1], Jim's note [2], and my reply to Jim [3] have made me  
realize that K == 1 is not such a low-risk alternative after all.

I believe what we are probably going to do for the allmydata.org  
"Tahoe" (don't call it "laugfs") v0.9.0 release (which will come out  
this week) is leave mutable files and directories with 3-of-10  
erasure coding.

This leaves open a (very small) possibility of colliding writes  
causing data loss.  More commonly than actual colliding writes at the  
filesystem layer, the current wapi offers know way to prevent  
*overwrites*, where someone else has added entries to a directory,  
and you didn't see their entries, yet, and then when you add some  
entries, you accidentally delete the ones that they added.

I am going to see if I can add a simple implementation of Tahoe Lock  
Files, following the recipe I earlier posted [4].

To make such a thing usable to client code such as Mike Booker's SMB  
layer, it needs to be exposed in the wapi [5].

Regards,

Zooko

[1] http://allmydata.org/trac/tahoe/ticket/332
[2] http://allmydata.org/pipermail/tahoe-dev/2008-March/000421.html
[3] http://allmydata.org/pipermail/tahoe-dev/2008-March/000424.html
[4] http://allmydata.org/pipermail/tahoe-dev/2008-March/000412.html
[5] http://allmydata.org/trac/tahoe/browser/docs/webapi.txt