Subject: Re: scsipi woes: can't call scsi command from kernel by ioctl?
To: Manuel Bouyer <>
From: Bill Studenmund <>
List: tech-kern
Date: 08/30/2005 19:29:21
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On Tue, Aug 30, 2005 at 10:07:09PM +0200, Manuel Bouyer wrote:
> On Tue, Aug 30, 2005 at 08:16:47PM +0200, Reinoud Zandijk wrote:
> Note that we already have IOCTLs for synchronise cache. Maybe you could
> reuse that ?

Yes, but that's only one call.

> > needs to be done regulary. In my userland code i used a disc abstractio=
> > that inquired the drive and handled all the specifics on=20
> > SCSI/ATAPI/disc/file devices. I could try to generalise it and to offer=
> > information in a IOCTL with the modification in the cd strategy that if=
> > certain type of media is found (CD recordables f.e.) the synchronise ca=
> > call is made on each switch from write to read. Without the sync the de=
> > won't accept read attempts (and certain other calls) possibly leading t=
o a=20
> > device lockout in situations where a cd writing program crases. If one =
> > lucky the timeout is less than 5-10 minutes :-S but some devices just w=
> > till bus/device reset.
> Yes; I think we should also allow writing though the raw or block device;
> so we could allow writing using e.g. dd (instead of writing only though
> the UDF filesystem).

Are you sure that these devices will support that? Perhaps I'm=20
overly-conditioned, but I have never looked to dd as a way to write CDs,=20
so I don't see why it should be a way to write UDF disks.

> > I've thought about implementing a /dev/mmc* device that is specific for=
> > cd/dvd/bd recordables/rewritables since they are a special breed of=20
> > critters quite different from normal cd-rom/dvd-rom. Seperating mmc dev=
> > from the generic `cd' devices also enables more targeted code to be=20
> > written. Code could also be simplified. How to use the detection framew=
> > i haven't figured out yet though. What i've read indicates that Linux a=
> > split off mmc devices from the older legacy CD driver.
> How much code would this represent ? I don't know if it's really
> worth it, and /dev/mmc vs /dev/cd could be confusing for users (not count=
> the third-party packages that would need to be adapted to use both :)

Can't say here.

However my understanding is that UDF is designed to work with MMC devices.=
As such, I don't think it's unusual to expect it to know about SCSI=20
commands, and to not work so well with non-SCSI/ATAPI devices.

Take care,


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