rsync - Oct 2007 - Using pre2 for backing up a mac

With the new ACL+xattr support and fake super (I'm glad this made it  
in!), it seems like my dream of being able to use rsync --link-dest  
to backup my mac is almost within reach!

If you take a look at
   http://blog.plasticsfuture.org/2006/03/05/the-state-of-backup-and- 
cloning-tools-under-mac-os-x/
you can get an overview of the meta-data which needs to be saved for  
faithful backups on a mac.

rsync 3pre2 now handles all but three items:
1. bsd flags
2. "locked flag" (supposedly finder meta-data)
3. creation date

There is a (broken) patch in the pre2 directory for backing up bsd  
flags. I gather these don't exist on linux? On a mac (and I assume  
BSD in general) you can get them from st_flags in struct stat and set  
them with chflags(2). If linux doesn't support them, it might be  
possible to copy the flags into an xattr.

The "locked flag" is actually just the bsd immutable flag; the author
of that article is wrong. So solving the bsd flag issue solves this.

The creation date is AFAIK a mac os specific piece of meta-data and  
can be accessed via the set/getattrlist + ATTR_CMN_CRTIME system call  
on a mac. Again, this meta-data might be reasonably converted into an  
extended attribute.

I've noticed the ACLs on a mac are only saved in an xattr on a linux  
machine when the fake-super option is used. I'm not sure if this is  
the right thing to do, and I'm not sure whether the bsd flags /  
creation date should behave similarly.

Would people be interested in a solution like this? What sort of  
toggle should be used to determine if the meta-data should be  
transported into an extended attribute? I'd be happy to whip up a  
quick patch for this if there's a consensus on how this meta-data  
should be converted.

On Oct 13, 2007, at 4:07 PM, Wesley W. Terpstra wrote:
> rsync 3pre2 now handles all but three items:
> 1. bsd flags
> 2. "locked flag" (supposedly finder meta-data)
> 3. creation date
>
> The creation date is AFAIK a mac os specific piece of meta-data and  
> can be accessed via the set/getattrlist + ATTR_CMN_CRTIME system  
> call on a mac. Again, this meta-data might be reasonably converted  
> into an extended attribute.
I've attached a patch which does this. Currently resource forks and  
finder info get placed into an extended attribute transparently by  
osx (com.apple.{ResourceFork/FinderInfo}). This patch makes another  
"extended attribute" called com.apple.CreationDate. The only issue  
I've found so far is that it gives warning when copying a symlink to  
linux as one can't set extended attributes there. It even works when  
copying from hfs to fat32 on the same mac. I don't understand where  
osx saves the creation date in a fat filesystem, but somehow it works!?

I admit it's a bit hack-ish to put this in the extended attribute get/ 
set methods, but this mimics the behaviour of the other osx-specific  
meta-data. Also, it seems reasonable to me that it should be copied  
when '-X' is specified. There is no fgetattrlist method, but it seems  
that sys_fgetxattr is actually never used b/c x_fstat is not used.

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