[Info-vax] Request description of UFS for VMS person

[Bill Gunshannon]

In article <00356ca1$0$20450$c3e8da3 at news.astraweb.com>,
	JF Mezei <jfmezei.spamnot at vaxination.ca> writes:
> Bob Eager wrote:
> 
>> As you say, unlink just removes a directory entry; all directory entries
>> are 'equal', so when the last one goes, the use count in the inode drops
>> to zero. At that point, the inode is cleared and the file blocks 
>> returned to free space.
>> 
>> On MS-DOS, the first byte of the directory entry was set to a special 
>> 'deleted' value, and file blocks were marked as free. Basic, but 
>> sufficient.
> 
> 
> Does this mean that "undelete" is not possible on Unix file systems
> because its logical equivalent to the entry in indexf is actually wiped
> out ?

Well, theoretically there is no reason why you couldn't rebuild a file.
BUt in actuallity, on any multi-user, multi-tasking system what do you
think the odds are that the freed blocks haven't been re-used between
when the file was deleted and when you decide to try to undelete it?

> 
> With VMS and DOS, it was possible to undelete files because entries were
> just flagged as available and remained until used by another file.

While the method used seems to make it somewhat easy, I think what I said
above has more to do with it.  If I can be fairly certain I haven't re-used
the freed blocks, then I can probably safely reconstruct the file.

bill


-- 
Bill Gunshannon          |  de-moc-ra-cy (di mok' ra see) n.  Three wolves
billg999 at cs.scranton.edu |  and a sheep voting on what's for dinner.
University of Scranton   |
Scranton, Pennsylvania   |         #include <std.disclaimer.h>