Re: 26 ways to set a device driver variable from userland

Matt Helsley
2005-10-19T23:39:35Z

On Wed, 2005-10-19 at 12:35 -0600, Christopher Friesen wrote:
> Kyle Moffett wrote:
>
> >> (4) sysfs
>
> > This is ideal for almost all device driver purposes.
>
> The one thing that I have yet to see a good solution for is
> transaction-based operations, where userspace passes in something (could
> be a command, a new value, a query, etc.) and expects some data in return.
>
> The ioctl() method is ideal for this, passing down a binary struct with
> a command/query member, and the driver fills in the rest of the struct
> based on the commnd.
>
> How do you do this cleanly via sysfs? It seems like you either double
> the number of syscalls (write to one file, read from another) or else
> you need to have sysfs files for every possible query/command, so that
> the input becomes implicitly encoded in the file that you are reading.
> This could end up creating a large number of files depending on the
> range of inputs.
>
> Are there any other standard ways to do this?
>
> Chris

Perhaps a connector would be appropriate here. Userspace could send a
netlink message to the connector with the query/command and the
connector could respond by sending appropriate results back to
userspace.

Cheers,
-Matt Helsley