Re: cd burning: kernel / userspace?

[Wakko Warner <wakko@animx.eu.org>]

Please keep me CC

> A script would be cool, but dd doesn't do the memory locking and real 
> time priority stuff.  I don't know how important this is - how old your 
> hardware would have to be for you to get "coasters" (buffer underun) 
> without it.

Agreed, however, I was attempting to make a point by saying dd.

> Theres an option in cdrecord to fixate an arbitrary disk (one without a 
> TOC for whatever reason), and one not to fixate the disk you're writing, 
> so it looks like fixation could and should be done on demand using an 
> ioctl.  You'd also need ioctls to deal with multiple sessions.

Already thought of this.  But how to deal with it, I don't know.

> I think most people would want a cdrwtool that basically pretends to be 
> cdrecord (in some ways ;), because thats the most intuitive way to do it 
> - even if you can do everything you want to with cdrwtool for the ioctls 
> and dd for the data.

That did come to mind, as long as I don't have to use dev=x,y,z (joerg you
listening?  Another user steps up to say he hates it =)    heheh.

> I've definitely underestimated the problems with my idea, and I can't 
> see any tangible benefits which couldn't be obtained by hacking

I can, like someone else specified.  Unlike windows, linux users can put
whatever filesystem (or just plain data) on a cd they choose.

They wanted to specify their cdrw to send stuff directly to it and change
cds.  Something like this (so long as the driver supports it too):

cdrwtool /dev/scd0 -ejectonclose -fixateonclose
	note could possibly do -dao with a fixed size.
	also, I don't know dump's options so I'm improvising
dump -D /dev/scd0 -B 700MB /home

When dump fills 700mb, it will close and await the user.  Since the driver
was told to fixate and eject on close, the cd comes out ready.  I understand
buffer underruns here and for starters, underruns aren't part of this
picture, it can come later (ie after proof of concept)
 
> cdrecord.  Idealistically, its the right thing to do - but in practice 
> its unessecary, I'm not up to the job, and its not attractive enough for 
> someone to pick up.  After packet writing is seamlessly merged into the 
> uniform cdrom driver it might start looking more important, and I might 
> have learnt enough to at least implement a proof of concept.  I'm still 
> interested in hashing out more details and potential benefits.

Frankly, I have found that growisofs is awkward to use.  I could hack it to
be better suited for what I wanted to do (I can't pipe data into it.  I used
to do mkisofs on one machine, send the data over the network and burn at the
same time.)  However, it's not as bad as dev=x,y,z

For me, if this were implemented in kernel, I could do this:
nail:~> mkisofs -r -no-pad /80g/debian/x/vol200 | \
	ssh vegeta 'cat > /dev/scd0'

(nail is a disk server, vegeta is the box with the burner on /dev/scd0,
that's my current setup)

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