Date: Sun, 13 Jun 2004 19:14:11 +0200 From: Poul-Henning Kamp <phk@phk.freebsd.dk> To: geom@freebsd.org Subject: GEOM class idea... Message-ID: <87385.1087146851@critter.freebsd.dk>
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OK, here is one of the more nasty ideas for a GEOM class:
Many of us read CD's into iso images, stick them on a harddisk and
mount them from there when we need to access them. This usually
costs us a md(4) vnode gadget, and that is really a waste.
Write a GEOM class which is a slicer, but it needs to work on CD9660
image headers as metadata, and work the following way:
Read in the first ISO image onto our archive disk:
dd if=/dev/acd0 of=/dev/ad8 bs=2k
On close, the disk is tasted, and our "geom_cdarch" class finds a
valid CD9660 volume description and attaches to the disk.
It extracts the image size from the CD9660 descriptor (offset 0x8050,
32bitLE. Repeated at 0x8054 as 32bitBE) and creates a slice with
this ISO image in it.
Since there is no valid CD9660 descriptor on the disk right after
this image, the remaining free space gets put into a special
slice ("ad8.freespace").
To read in the next ISO image:
dd if=/dev/acd0 of=/dev/ad8.freespace bs=2k
On close the geom_cdarch class looks for a valid CD9660 volume and
if it finds one, creates a new slice and recreates the freespace
slice with the space now available, and we can repeat the process
until we run out of space.
Any takers ?
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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