Re: OS X 10.6 (Snow Leopard) HFS+ File Compression

[Mike Bombich]

HFS compression can be preserved as long as the relevant xattr(s) and flags on those files are preserved.  A compressed file has the compressed data in a hidden xattr (com.apple.decmpfs if < 4Kb, com.apple.ResourceFork if more), and has the UF_COMPRESSED flag set (decimal 40).  When rsync encounters a file like this, it should ignore the data fork of the file, which will appear to contain normal, uncompressed data.  It should also pass a special flag to the xattr calls to expose the decmpfs xattrs. I've already implemented this in rsync (3.0.6), I just hadn't taken the time to craft the HFS-compression-specific changes into a patch.  I did that this evening and attached it below.  These are changes against the 3.0.6 base, plus the crtimes, fileflags, and backup-dir-dels patches.  It should work, at minimum, against the 3.0.6 base plus the fileflags patch (that patch is required). Let me know if it doesn't work for you, it's entirely possible that I overlooked something in the extraction. Mike

rsync_3.0.6-hfs-compression_20091027.diff
Description: Binary data

On Oct 27, 2009, at 11:08 PM, Matt McCutchen wrote: On Tue, 2009-10-27 at 23:38 -0400, Tony wrote: When rsync 3.0.6 copies files with HFS+ File Compression, the new   extended attribute decmpfs is not preserved, and the UF_COMPRESSED   flag is not set on the destination and the destination file is not   compressed. I examined the destination file as described in ars technica  (with ls   and xattr from a 10.5 Leopard boot), and the compressed data is moved   from the resource fork to the data fork, and the extended attributes   '@' are removed from the file. As far as I know, only ditto in 10.6 can handle HFS+ File   Compression.  (I even tested a 'clone' with disk utility (file copy,   not block), and it also failed (block copy, of course works). Rsync is just reading and writing files via the filesystem API; it has no access to any of the flags or xattrs used to implement the compression. I guess the filesystem doesn't compress new files by default.  If it had an API to request compression, rsync could use that API when writing the destination files.  Unfortunately, the API ditto is using appears to be private to Apple.  See the post from brkirch beginning "The first thing that I tried to do" on this page: http://www.macosxhints.com/article.php?story=20090902223042255 So anyone interested in making rsync compress the destination files would probably have to copy the relevant code from afsctool.  This could be shared as a patch; I feel quite sure it would not be adopted in the main version of rsync. -- Matt -- Please use reply-all for most replies to avoid omitting the mailing list. To unsubscribe or change options: https://lists.samba.org/mailman/listinfo/rsync Before posting, read: http://www.catb.org/~esr/faqs/smart-questions.html

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