using rsync with Mac OS X
tgeernaert at merlinsoftech.com
Wed Feb 6 06:16:19 EST 2002
OK, I'm brand new to this group, brand new to rsync, brand new to
unix in general. I'm trying to play catch up with this discussion
so there are likely many misconceptions that I have about these
My goal is to create a tool that does backup and restore only
transferring changes. It will connect to a server running Linux
from Mac OS X and preserve all metadata without the user ever
knowing there is an issue. I've found the rsync algorithm is a good
start and it sounds like you all have the same idea.
I don't think I like the idea of the MacBinary solution, in that I
can see some configuration of the tool that the user will have to
worry about. We obviously don't want the overhead of flattening files
without forks or files that have FileInfo that can be determined from
other metadata strategies. The user might have to maintain a list
of files they use... How do I handle this file or that (á la mac cvs
I see another user experience issue with the MacBinary solution and
the protocol change. What do the files look like when they get
backed up? If I connect to the server via the finder am I going to
see a bunch of files that are 'archived' or do I get the real deal.
I would hate to use rsync if I couldn't just go and grab the files
that got backed up. Not that running the file through stuffit is a
big deal but it going to seems like a bit of a kludge to the user
even if the solution is in fact much more elegant. What format is
this new protocol going to produce? Will the only way to get to the
files be to use the rsync client? Sorry, that's just not acceptable.
The only solution left is to pre-process the file by splitting it
before before creating the change lists. There will have to be some
intelligence about what method of splitting was used on the server
but I'm positive that couldn't be too hard to determine. Please
tell me if I'm way off base here.
One other question that I'm sure will show my ignorance of Darwin
development. What is the issue with using the high level API's if
the output is compatible with the other platforms running rsync.
What is the advantage of trying for posix purity or code at the
"Darwin level" if the code is only going to be used on Macs running
the higher level stuff anyway? If you don't have a forked file
system why would you care if you don't know how to handle forks?
I'm planning on taking this project on full time and we would all
benefit if we can all agree on a direction.
Lets get this thing going,
> Mark Valence wrote:
> So, that's one vote each for options 1, 2, and 3 ;-)
> I agree that the ideal implementation would support HFS+ as well as
> netatalk's .AppleDouble scheme, Mac OS X's ._<filename> scheme, and
> MacBinary for all the rest. This can certainly be a goal of the
> implementation, but personally I am interested in the HFS+ on Mac
> OS X part of the problem.
> My implementation, whether it is MacBinary based or a change the
> the protocol, will leave room for these alternative schemes. Right
> now, I am thinking that MacBinary is the way to go. This doesn't
> give the flexibility and extensibility that a protocol change would
> give, but it does have the benefit of supporting existing rsync
> Chris I., I'm not sure what you mean by "done at the Darwin level".
> If you mean that it should be done based on Darwin/BSD APIs and not
> Carbon/Cocoa APIs, then I am in full agreement with you. The calls
> that I'd use to access the resource fork are posix calls
> (essentially, it's just an open() call), although the calls to get
> HFS metadata are Mac OS X-specific (but not Carbon calls).
> Anyway, I'm still mulling all this over, so any suggestions are
> more than welcome. Once a path is chosen and code is written,
> things will be harder to change ;-)
> Chris Garrigues wrote:
>> A quick thought about implementation details: It would be nice if
>> this were
>> done in such a way that if I were to rsync from a non-OSX netatalk
>> onto an OSX system the .AppleDouble directories would be merged
>> back into the
>> files, and conversely if I were to rsync from an OSX system to a
>> system the resource forks would be split into .AppleDouble
>> I guess this would be simplest with scheme 2 above.
> David Feldman wrote:
>> I'm not familiar with netatalk, but along a similar line, Mac OS X
>> stores resource forks and metadata differently on HFS+ and
>> single-fork volumes (such as UFS or NFS). If you copy a file from
>> an HFS+ volume over to a single-fork volume using the Finder it'll
>> split the pieces apart and save the resource fork and metadata
>> under variations of the original filename. I don't remember the
>> exact names but I think they're in the Mac OS X System Overview
>> document...something like ._<original filename>.
>> If there's a way I can help with the porting effort please let me
>> know. I don't know a lot about the lower-level details, but do
>> know C, C++, Cocoa, etc. and would be interested in looking at the
>> BSD-level info you have on transferring OS X files.
>> As I stated in my earlier message, my primary interest is
>> synchronization of desktop and laptop, though backup would be
>> terrific too. I'm pretty sure there are a lot of OS X users out
>> there in need of both. I'm currently synchronizing with a shell
>> script that uses ditto.
> Chris Irvine wrote:
>> I would lean toward option "1" for several reasons. Primarily it
>> could probably inter-operate safely with non-HFS or older versions.
>> How about a flag that changes the mode to detect named forks and
>> encode them in-line. These encoded files could be safely synced to
>> non-forked storage destinations or tape. A simple tag passed at
>> the beginning of a session could notify the destination that
>> MacBinary decoding could be attempted if available.
>> I also understand the need for named resource files for systems
>> like netatalk. The problem with this is that every named fork
>> system is different: netatalk, Xinet, Helios, OSX Finder. This is
>> a lot to chew. I would rather the user post process files to get
>> them into the named fork method if they must. If you are going
>> between two systems using the named fork technique, this whole
>> process is unneeded.
>> Option "3" might be the best. It seems to me that this could end
>> up requiring a lot of changes to the protocol.
>> It should also be noted, that a project like this should be done
>> at the Darwin level. There have also been discussions on the
>> darwin-development list in June 01. No one really stared anything,
>> however they did discuss at length how access to resource forks
>> might be done while stying inside posix calls.
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