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File System Management Is Headed for Trouble

Feb 24, 2009, 15:32 (5 Talkback[s])
(Other stories by Henry Newman)

[ Thanks to Paul Shread for this link. ]

"POSIX today contains information on each file on access time, creation time, user, groups, and permissions. That is about the extent of what POSIX provides. All of this is accessible via the stat() system call and nothing else. POSIX basically defines extended attributes using the getattr() and setattr() system calls. This is a standard way to extend the information that is carried in a file.

"The problem is that the framework exists for a file system to populate the attributes, but there is no common set of attributes that works across file systems. Take the following example. Let's say a vendor wants to support an HSM interface. There is a common framework called DMAPI that many HSMs use. The vendor might implement the DMAPI standard using POSIX extended attributes and populate the DMAPI information as part of those extended attributes. When the file system can't open the file, the file system will then check the extended attributes and find that the file is under HSM control. What if you copy that file to another file system or a different operating system? If you are using the standard copy commands like cp or you ftp the file, all the information about the file and in the extended attribute will be lost."

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