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

["Christopher Friesen" <cfriesen@nortel.com>]

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