On Thu, Oct 24, 2002 at 12:46:12AM +0200, Oliver Neukum wrote:
> >
> > Seriously, this is a userspace issue. The driver can set some initial
> > values that it things is good, but in the end, root can change them to
> > whatever it wants to, nothing new there.
>
> Most definitely not true.
> 1. You make it impossible for drivers to implement exclusive open.
> This assumption is built into all V4L drivers.
Wait, we aren't streaming video data out a driverfs file. We are just
exporting or writing a single value for a single device. What needs to
be "exclusive" for something like that?
> 2. You now have changes of permissions and ownership
> which are not atomic.
Who's changing anything? Userspace? I don't see the kernel doing any
changes. Or am I just confused here...
> > Even so, open is not needed to be passed to the driver. Yes, of course
> > you need to do a open() call from userspace, and driverfs will get that
> > and handle the reference counting properly for the device that is
> > attached to that file.
>
> You can do that for the module usage count. For reference counting
> of a driver's internal data structures you cannot depend on driverfs.
Um, driverfs knows the device that every attribute file that has been
created, so it knows the needed information.
> The alternative is for the driver to treat any read/write through driverfs
> as a combination of open+read/write+close.
> There seems to be some misunderstanding. Do you want to prevent
> disconnect() while read/write is running ?
No, we can't prevent that. We should have the following:
open(/sys/root/..../usb.../foo_value) returns file_handle
-- disconnect happens
-- device gets cleaned up
read(file_handle) returns -ENODEV, or some other error value.
close(file_handle)
Look ok?
Yes, it's not that way today, but we are getting there...
> > The goal is to not have drivers get driverfs (soon to be sysfs)
> > implementation wrong. The current driver interface to it is quite
> > simple, and we want it to stay that way.
>
> The usage recently seen on usb-devel was totally screwed, so I am
> judging by recent experience.
The current device values that the usb core exports through driverfs are
screwed? How so?
thanks,
greg k-h
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