Re: albods

Helge Hafting (helge.hafting@c2i.net)
Sun, 11 Jul 1999 16:06:22 +0200


> Hi, all. I see this discussion is still going on. Here's an
> interesting idea for you (not mine, some other guy suggested it in
> private email, but he doesn't seem to have taken up my suggestion of
> posting it to linux-kernel).
>
> His idea is to used a modified loop driver, and build a filesystem in
> a regular file, then mount this FS if you want to access different
> data "streams".
>
> When creating the file, make it huge, but filled with holes. The
> modified loop block driver would fill in holes as required (assuming
> it doesn't do this already: I haven't looked).

Making the file huge will waste lots of space. How about
this userspace solution:

Use the loop-mount way with a filesystem with very low overhead,
similar to romfs. Start with a small file, and extend it
when necessary. The filesystem must of course be designed
in a way that allows extension by simply appending more space.

Extending the file can be handled by a standardized library that
takes care of messy details like umount-extend-remount. This library
might have its own implementation of "fwrite()" so it can be smart
about extending the file.

A low-overhead filesystem could fragment a lot, but this can be helped
by letting the albod-library have a idle-priority thread doing
defragmentation when such files are in use.

We get:
* A compact file useful for ftp, cp, and other transfers.
* Many files in one for albod-aware apps (that use the
appropriate library)
* GUI Filemanagers may do the loop-mount thing when users click
on this kind of file.

Helge Hafting

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