Can we make the io_poll queue attibute read-only

Can we make the io_poll queue attibute read-only

[Christoph Hellwig]

Hi Jens,

while looking at the polling code I wonder if we have to keep supporting
the change of the io_poll attribute and thus the poll flag on a live
queue.  The support to change this goes back to before supporting the
explicit poll queues, and was used as the prime interface to enable
polling.  Now that we use explicit poll queues the driver specific
paramters to set them up work as the prime interface to enable polling.
They can still be changed at runtime, although much more invasively
(i.e. controller reset in nvme).  The upside is that we don't need
to bother with draining the bios and two queue flags, and don't have
a confusing duplicated user interface.

Re: Can we make the io_poll queue attibute read-only

[Jens Axboe]

On 4/29/21 1:32 AM, Christoph Hellwig wrote:
> Hi Jens,
> 
> while looking at the polling code I wonder if we have to keep supporting
> the change of the io_poll attribute and thus the poll flag on a live
> queue.  The support to change this goes back to before supporting the
> explicit poll queues, and was used as the prime interface to enable
> polling.  Now that we use explicit poll queues the driver specific
> paramters to set them up work as the prime interface to enable polling.
> They can still be changed at runtime, although much more invasively
> (i.e. controller reset in nvme).  The upside is that we don't need
> to bother with draining the bios and two queue flags, and don't have
> a confusing duplicated user interface.

I think so, doesn't make much sense anymore. There's no point in
configuring for poll queues and then disabling it through sysfs.

Rather than make it RO and risk breaking apps, why not just ignore the
write?

-- 
Jens Axboe