Messages in this thread |  | | | Date | Wed, 21 Dec 2005 09:46:38 +0100 | | From | Jesper Juhl <> | | Subject | Re: [PATCH - 2.6.15-rc5-mm3] Allow sysfs attribute files to be pollable. |
On 12/21/05, Neil Brown <neilb@suse.de> wrote: > On Wednesday December 21, jesper.juhl@gmail.com wrote: > > 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? > > You miss an intermediate event I guess. > > If you have a stream of events where you absolutely want to see every > one of them, then you want something like a character-device (or one > of several other alternative). > That is not what this is for. > > However very often you don't need to see every single event. You just > need to know when state has changed so you can respond to the new > state. > That is what this patch is for. > > Does that answer your question? > Yes it does. Thanks.
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