Re: [PATCH 0/4] Fiemap, an extent mapping ioctl - round 2

[Andreas Dilger <adilger@sun.com>]

On Jun 30, 2008  19:01 -0700, Brad Boyer wrote:
> What would you expect as reasonable behavior for an FS type that
> doesn't have distinct storage for directories? On HFS and HFS+, the
> directory information is completely synthetic based on the parent
> ID of each file. A directory has no actual data dedicated to it 
> other than the basic metadata that would be in the inode in ext3,
> and readdir just walks the catalog tree and finds all the entries
> that say they have the directory you want as a parent. They are
> sorted that way, so it's not as bad as it sounds for performance.
> 
> Would it be reasonable for a filesystem like this to just say that
> a directory has no extents at all? You can open a directory and
> seek to an offset, but that doesn't logically map to any place
> on the disk. Is this going to cause problems?

Even though the directory data isn't stored in a separate "file",
the inodes that make up the "directory" still consume space on disk.
If I were writing a FIEMAP handler for such a filesystem, I'd probably
return the byte range of the "catalog tree" that match the directory
"parent".

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.