Meelis Roos wrote:
>
> sfgd> What you see is a result of a design flaw in the Linux kernel:
>
> sfgd> A "natural" implementation would look like this:
> sfgd> - one or more SCSI parallel Host adapter drivers
> sfgd> - one oe more SCSI serial Host adapter drivers (e.g. ieee 1034 ???
>Fire wire)
> sfgd> - one or more IDE packet SCSI hostadapter drivers
> sfgd> All working with a single SCSI glue library to:
> sfgd> - CD-ROM driver
> sfgd> - Tape driver
> sfgd> ...
>
> AFAIK this is how Linux works. There are host adapters - real adapters,
> ide-scsi virtual adapter, usb/i2o/parallel adapters (don't know whether IEEE
> 1394 scsi exists already). And then there are general high-level drivers liks
> scsi disks, scsi cdroms, scsi tapes etc. The same scsi cdrom driver is used
> for "real" scsi cdroms and ide cdrom (in case the ide interface uses ide-scsi
> virtual host adapter). I see no problem with Linux. I think you are seeing
> hallucinations (sp?) here.
>
> The original problem was with choosing between ide-scsi (the virtual scsi
> adapter that takes over an ide interface) and native ide cdrom driver (ide-cd)
> for this interface. I find it natural that the generic scsi interface needs a
> scsi host adapter (virtual or not) below it to function. So ide-scsi must be
> used with this ide interface, not ide-cd. The cdrom becomes scsi cdrom to the
> rest of the system - so what?
Well put.
What I think Joerg objects to is needing multiple libscg
interfaces for Linux (several versions of sg [including his]
and pg) with a possibility of more to come. When a pseudo
driver such as ide-scsi is used then some magic is needed to
stop the native ide stack taking ownership of the device.
Linux has allowed various IO subsystems to develop independently
of one another. Where the need arises, cross over (or pseudo)
drivers such as ide-scsi are written. FreeBSD has a very good
SCSI implementation based on CAM (part of the SCSI standard).
NT/W2K has its overarching Storage Driver Architecture and
ASPI that generalize over various IO architectures. The
freedom of the various IO subsystems in Linux allows advances
in new areas such as 100 MB/sec IDE and I2O without the inertia
of a grand IO subsystem design or using a foreign command set.
All approaches have advantages over the others in certain
categories.
In the area of cd writing, Linux is beginning to offer packet
writing facilities through the cdrom subsystem. This will
represent a higher level interface into the kernel for
this function than currently offered by sg or pg.
Doug Gilbert
linux sg maintainer
P.S. Linux offers no SCSI capability over IEEE 1394 yet.
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