Using binary attributes for configuration sysfs entries

[Greg KH]

On Wed, Mar 13, 2019 at 12:02:02PM +0530, Jay Aurabind wrote:
> Hi,
> 
> Before I send this patch to actual mailing list, I'd appreciate if
> someone could tell me if this is a bad idea!
> 
> The driver in staging for pi433 (a wireless transceiver) uses IOCTLs
> at the moment. I wish to add a sysfs interface to it that control the
> various transmission and reception parameters. In the ioctl interface,
> it uses two structs that have about 40 parameters in total.
> 
> For the corresponding sysfs interface, since there are a lot of
> parameters, would it be justified to use the same binary format though
> sysfs_create_binary_file() ? The rationale is that it would be easier
> to simply pack all the config options in the struct and send it in
> once rather than individually write 40 files. This is what the
> attached patch follows. Interface is added only for reception
> parameters as of now.

binary sysfs files are only allowed for "pass through" data, where the
kernel does not touch the information at all and only passes it from the
hardware, to userspace directly (or the other way around).  It can not
be used for data that the kernel actually knows about and modifies /
acts on.

An example of valid binary sysfs files are USB and PCI device
configuration information (read directly from the hardware), or firmware
files that are send from userspace directly to the hardware without the
kernel knowing what the data is.

You can't use a binary sysfs file for ioctl-like data, that's not
allowed, just use an ioctl for that.  Or better yet, use a common api
interface for it, to match the other types of devices.

hope this helps,

greg k-h