On Mon, 19 Feb 2007, Douglas Gilbert wrote:
> Alan,
> The SG_GET_RESERVED_SIZE ioctl is also defined in
> the block layer, see block/scsi_ioctl.c .
Ah, I didn't know that. (Or more likely, I used to know and have since
forgotten.) Thanks for pointing it out.
> I suspect it is just a kludge to fool cdrecord that it
> is talking to a sg device. [One of many kludges in the
> block SG_IO ioctl implementation to that end.]
> So perhaps the block layer versions of SG_SET_RESERVED_SIZE
> and SG_GET_RESERVED_SIZE need to be similarly capped.
Yes. In fact one of them already is, but the other should be too.
> Actually I think that I would default SG_GET_RESERVED_SIZE to
> request_queue->max_sectors * 512 in the block layer
> implementation (as there is no "reserve buffer" associated
> with a block device).
Okay.
Come to think of it, the reserved_size value used when a new sg device is
created should also be capped at max_sectors * 512. Agreed? I can't see
any reason for ever having a larger buffer -- it would be impossible to
make use of the extra space.
Alan Stern
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