On 5/4/05, Grant Coady <grant_lkml at dodo.com.au> wrote: > I have queries, is there a reason why sysfs doesn't return multiple > values? So instead of asking for a filename with encoded array index, > one gets a list of values? One line per value, it works, easy to use > as 'flat' datafiles. And it removes index from filename. the many > to many (eg. temp channel -> fan speed control channel) can be resolved > same as database normalisation. As I understand it this was a deliberate decision to ease the problems experienced with 2.4 proc entries where userspace programs would have to parse the contents to extract specific information, and every time the format of the contents (e.g. number/order of columns) changed all these userspace apps would be broken. It was decided presenting the specific information per file was a much simpler and more sensible interface. I tend to agree. > > Secondly is there a design document I've missed for this? What does > dynamic sysfs look like to user? sub-directory per device/block or > in the same directory level namespace? I damaged the patches somewhere, > one didn't apply so couldn't 'see' it yet. This patch just changes the way device attributes are created, it does not change the external sysfs interface at all. At the moment every driver in the kernel (as far as I can see) defines a set of static device attribute structs which are used by the driver when calling the sysfs_create_file function. Greg was referring to creating non-static attributes or creating device attributes at runtime (as bmcsensors does) as dynamic. Due to the nature of the sysfs device callbacks, each device attribute in general requires a separate sysfs show/store callback function. This has led to the kludge of a large number of macro defined callbacks that are virtually identical. This leads to two problems, first we can only define a limited and pre-determined number of sysfs callbacks and hence device_attributes (in the case of bmcsensors it can have an unlimited number of sensors), secondly a whole load of redundant code is generated by the macros and is a large waste of space. By adding a void * attribute member to the device_attribute structure and passing these to callback functions we allow drivers to greatly reduce the number of callback functions and also allow for a potentially unlimited number of sysfs entries to be created. I refer to these callbacks as dynamic because they change their function depending on what is passed to them. Yani
