Re: VFS

Bill Hawes (whawes@star.net)
Tue, 18 Nov 1997 15:00:19 -0500

Andrew E. Mileski wrote:
> UDF is used on much bigger disks (like DVD), it also can span media
> (up to 64k volumes). It really neads a 48-bit inode number.
>
> I think I found a passable solution though. Use the lower half of the
> 64-bit unique ID of the _first_ file entry for a file.
>
> The UDF spec recommends the unique ID be less than 2^32 for Macintosh
> compatibility, but it doesn't insist on it. [This limits the number of
> files on all media, and the number of file revisions on write-once media.]
> So we'll have to scream if the upper half of the ID is ever > 0.
>
> It is possible to access a file by this inode number, but it would be
> slow to open as the file system must be searched.

Does the UDF volume include an index to translate from ID number to
block number, or could you build this dynamically?

Using a stable ID number for your inodes would allow the filesystem to
be exported, which would be a desirable feature if it's at all
possible. The lookup problem could be covered up by a dynamic index, or
perhaps some other clever schemes.
(For example, a well laid out UDF volume might have a predictable
pattern of IDs allowing you to estimate the block position before having
gone there.)

Regards,
Bill