Messages in this thread | | | Date | Wed, 21 Dec 2005 00:28:51 +0100 | From | Jesper Juhl <> | Subject | Re: [PATCH - 2.6.15-rc5-mm3] Allow sysfs attribute files to be pollable. |
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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. > + */
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