On Mon, 2007-10-29 at 12:24 -0400, Jeff Garzik wrote:
> James Bottomley wrote:
> > Ah, OK; I haven't communicated what we need very clearly. We need a way
> > to see if the event is supported by the device, as well as a way to turn
> > it off. For some of the events (possibly not the SATA AN one, since I
> > know all SATA devices will be well behaved) there's going to be a need
> > to deal with berserk or broken devices that become trigger happy, so
> > turning off the event will be a useful (and possibly essential) way of
> > coping.
>
>
> That's possible with the presented interface[1]:
>
> # see if event is supported
> cat $path/evt_media_change
>
> # turn off event to deal with broken/beserk devices
> echo 0 > $path/evt_media_change
>
> Some sillyhead can always do
>
> echo 1 > $path/evt_some_event_my_device_does_not_support
>
> but that will be obviously be a no-op because their device simply will
> not send such events.
>
> Granted ls(1) is no longer a method for viewing supported-at-boot-time
> list of events -- ls(1) in the presented interface lists what events the
> _kernel_ supports, and cat(1) is used to discover which events are
> actually enabled.
>
> I think that is the only difference between our two positions: [if I
> understand you correctly] you want ls(1) to be able to list the device's
> supported events. However, I feel that is inconsistent: for your
> proposal, userspace must perform two checks in order to determine a
> feature's availability: 1) does the file exist? 2) is the file context
> non-zero?
Yes, I agree ... however, open file is one op for the user -ENXIO means
device doesn't support the event; value indicates whether the event is
currently triggering.
I just would rather we use the file exists if device supports event,
because it's consistent with all the rest of our SCSI interfaces.
> Regards,
>
> Jeff
>
>
> [1] modulo my comment from the original email in this thread:
> > * I was slack and did not bother to implement the 'set' operation
> > for the attributes. This can easily be done at a later time in a
> > separate patch.
James
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