Re: SG_IO ioctl (was: mode sense blacklist how)

[Pat LaVarre <p.lavarre@ieee.org>]

Offline kindly I'm reminded to distinguish a compelling third "pro" for
SG_IO via block/scsi_ioctl.c:

> > Designing an lk 2.6 user app to recommend more prominent device names
> > like /dev/hdd and /dev/scd0 in place of less prominent /dev/sg$n names
> > thereby steers people into using the less robust pass thru of SG_IO via
> > block/scsi_ioctl.c.
> 
> Pat,
> Well it's a trade-off. If you use the SG_IO in
> the block layer then:
> 
> Pros:
+ -- - works with ide-cd kernels, not just with ide-scsi kernels
>    - convenience (for block devices)
>    - no device mapping problems (sd <-> sg) **
> Cons:
>    - no help for "non-block" devices: tapes, enclosures,
>      OSD, etc
>    - inherit block layer policy (e.g. 128 KB xfer limit,
>      direct IO alignment)
>    - unable to interrupt a SCSI command in progress with
>      a signal
>    - associated ioctls are dummies or not there, hence unable
>      to reset device/bus/host (for example)
>    - no driver or host error reporting (only SCSI status)
> 
> I'm sure more "cons" will come to light and some will be
> addressed. There is probably enough there already to give
> the cdrecord author pause for thought.

Pat LaVarre