[darcs-devel] Re: darcs is unable to operate with a repository on OpenAFS

[Bennett Todd]

2005-06-08T14:42:55  via RT:
> $ darcs init
> 
> Fail: takeLock: unsupported operation (Invalid cross-device link)
> [...]
> For reasons beyond my understanding, an AFS subdirectory is treated as a
> different mount than the parent, despite being on the same volume. 
> Since hard linking doesn't make sense across different mounts, darcs is
> barfing.

Not exactly "an AFS subdirectory is ... a different mount". Rather,
AFS doesn't support hard links between directories. It's one of the
many extraordinary and wonderful ways in which AFS is not like a
Unix filesystem. Here are some more:

- Unix permissions have no meaning or effect, except where
  applications explicitly read the permissions and make decisions
  --- the filesystem itself ignores them. Instead, AFS ACLs have
  the only control there is.

- <dev,ino> pairs are not unique. All AFS "volumes" (a much smaller,
  lighter-weight concept than unix "filesystem") show up with the
  same st_dev, and the st_ino is taken by combining some (but not
  all) of the bits from the AFS file number, and some (but not all)
  the bits from the AFS volume number.

- st_nlink for Unix directories is always 2 plus the number of
  subdirs. Not in AFS, AFS mount points are reported by stat(2) as
  directories, but don't participate in st_nlink. Remember to use
  -noleaf when asking GNU find to traverse AFS.

- files being written are flushed back to the server only when the
  file is closed. That is, if your tokens haven't expired first, in
  which case everything you wrote is discarded, lost forever.

AFS is a cute academic hack, the sort of work that's great to see in
universities, rich fertilizer for growing research papers. It's a
catastrophic mistake letting such a prepostorous kludge out of the
academic hothouse and trying to use it to get real work done.

-Bennett
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: not available
Url : http://lists.osuosl.org/pipermail/darcs-devel/attachments/20050608/9d002014/attachment.pgp