Re: [PATCH - 2.6.15-rc5-mm3] Allow sysfs attribute files to be pollable.

Jesper Juhl
2005-12-20T23:28:53Z

On 12/21/05, Neil Brown <neilb@suse.de> wrote:
>
> I suggested an early of this patch some time ago to see if it was an
> acceptable approach and got zero feedback, which presumably means it
> is perfect:-)
>
> I've now reviewed it, fixed up the bits I didn't like, and tested it.
> It works and I am happy with in.
>
> So: I would like to submit it for inclusion in a future kernel.
>
> Comments, or acks, please :-)
>
[snip]
> +/* Sysfs attribute files are pollable. The idea is that you read
> + * the content and then you use 'poll' or 'select' to wait for
> + * the content to change. When the content changes (assuming the
> + * manager for the kobject supports notification), poll will
> + * return POLLERR|POLLPRI, and select will return the fd whether
> + * it is waiting for read, write, or exceptions.
> + * Once poll/select indicates that the value has changed, you
> + * need to close and re-open the file, as simply seeking and reading
> + * again will not get new data, or reset the state of 'poll'.

What if the value changes again between me closing and re-opening the file?

> + * Reminder: this only works for attributes which actively support
> + * it, and it is not possible to test an attribute from userspace
> + * to see if it supports poll.
> + */

--
Jesper Juhl <jesper.juhl@gmail.com>
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