On Wednesday 08 March 2006 00:23, Greg KH wrote:
> >
> > Hmm, what is the policy for attr->show()? With hotplug variables we
> > return -ENOMEM if there is not enough memory to store all data, but
> > what about attributes? Should we also return error (and which one,
> > -ENOMEM, -ENOBUFS?) or fill as much as we can and return up to
> > PAGE_SIZE?
>
> Remember, sysfs files are supposed to be small, you are an "oddity" in
> that you have a much larger buffer that you can return due to the wierd
> aliases you have.
>
> Truncating the buffer is probably good as we want userspace to get some
> information, right?
>
> > With sysfs not kernel nor application can really recover
> > if attribute needs buffer larger than a page. Or just rely on BUG_ON
> > in fs/sysfs/file.c::fill_read_buffer()?
>
> How about just making this a binary attribute, then you can handle an
> arbitrary size buffer and don't have to worry about the PAGE_SIZE stuff
> (but it makes it more code that you have to write to handle it all,
> there are tradeoffs...)
>
I really don't believe that we ever going to cross 4096 boundary for any
single input attribute, but just to code defensively we need to decide
what to do if we ever encounter a crazy device. Just truncating to
PAGE_SIZE is easiest so that's what I am going to do.
--
Dmitry
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