[Dirvish] Dirvish/rsync thinking partition is 'new'

Paul Slootman paul at debian.org
Mon Mar 7 11:47:23 UTC 2011


On Sun 06 Mar 2011, Dale Amon wrote:
> 
> Oh futz. Hard links don't allow a new directory entry with different
> metadata. I had not thought that all the way through.

I get a sense of misunderstanding here about how files, directories and
inodes really work, so I'll volunteer some info now :)

An inode is a data structure that stores meta information about a
"file" (using "file" here in its broadest sense - it can be a regular
file, a directory, a device node, a named pipe, etc.). The inode stores
the owner/group/permissions/timestamps, as well as the type of file it
is, and where appropriate also has info on how to find the data blocks.

A directory is a data structure that contains pointers to inodes.
More than one pointer to a given inode may exist, that's what hard links
are. The owner/group/permissions aren't stored in the directory;
basically all a directory is, is a name to inode mapping.

So to have the same file contents with two different sets of metadata on
a filesystem, the data needs to be duplicated.
(For simplicity I ignore copy-on-write filesystems here, as that
introduces a complete new layer of information to the filesystem.)


Paul


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