• Open Menu Close Menu
  • Apple
  • Shopping Bag
  • Apple
  • Mac
  • iPad
  • iPhone
  • Watch
  • TV
  • Music
  • Support
  • Search apple.com
  • Shopping Bag
 

Lists

Open Menu Close Menu
  • Terms and Conditions
  • Lists hosted on this site
  • Email the Postmaster
  • Tips for posting to public mailing lists
Should I be concerned about the XATTR_SHOWCOMPRESSION option?
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Should I be concerned about the XATTR_SHOWCOMPRESSION option?


  • Subject: Should I be concerned about the XATTR_SHOWCOMPRESSION option?
  • From: James Bucanek <email@hidden>
  • Date: Tue, 21 Feb 2012 16:16:28 -0700

Greetings,

This question is in the context of a backup application, so I'm concerned with backing up and restoring extended attributes on a filesystem.
Should I be concerned with the XATTR_SHOWCOMPRESSION option to
the listxattrs() and getxattr() functions?
The documentation says:

XATTR_SHOWCOMPRESSION
getxattr() and fgetxattr() will return HFS Plus Compression extended attribute name (if
    present) for the file referred to by path or fd.

I'd like to know what these special xattrs are and how they should be handled (i.e., when restoring should these xattrs be set before the data forks are written, etc.).
I thought I would see what files had them, but I can't find any. :(

As a test, I wrote the following loop and ran it as root on every file of a relatively recent Lion install.
    int i;
    for (i=1; i<argc; i++)
        {
        ssize_t nameListLength, altListLength;
        // Get the size of the extended attributes name list
        nameListLength = listxattr(argv[i],NULL,sizeof(names),XATTR_NOFOLLOW);
        if (nameListLength<0)
            {
            NSLog(@"%s; errno=%d",argv[i],(int)errno);
            continue;
            }
        if (nameListLength==0)
            {
            //NSLog(@"%s; no extended attributes",argv[i]);
            continue;
            }
        altListLength = listxattr(argv[i],NULL,sizeof(names),XATTR_NOFOLLOW|XATTR_SHOWCOMPRESSION);
        if (nameListLength!=altListLength)
            {
            NSLog( ... print out all xattrs ... );
            }
        }

The results were ... nothing. Not a single file on the volume returned a different set of xattr names when the XATTR_SHOWCOMPRESSION option was included.
--
James Bucanek


_______________________________________________
Do not post admin requests to the list. They will be ignored.
Filesystem-dev mailing list      (email@hidden)
Help/Unsubscribe/Update your Subscription:

This email sent to email@hidden


  • Follow-Ups:
    • Re: Should I be concerned about the XATTR_SHOWCOMPRESSION option?
      • From: Chris Suter <email@hidden>
  • Prev by Date: Re: jhfs+ question, jhdr size
  • Next by Date: The mysteries of the XATTR_SHOWCOMPRESSION option
  • Previous by thread: Re: jhfs+ question, jhdr size
  • Next by thread: Re: Should I be concerned about the XATTR_SHOWCOMPRESSION option?
  • Index(es):
    • Date
    • Thread