Re: [PATCH v5 08/15] cxl: Add support for FWCTL get driver information callback

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Feb 12, 2025 at 01:18:01PM -0800, Saeed Mahameed wrote:
> > +/**
> > + * struct fwctl_info_cxl - ioctl(FWCTL_INFO) out_device_data
> > + * @reserved: zero
> > + */
> > +struct fwctl_info_cxl {
> > +	__u32 reserved;
> > +};
> 
> I would add some useful info such as: num_user_features, mbox->feature_cap,
> etc ...
> 
> Maybe if the callback is not implemented by the fwctl driver, then fwctl
> subsystem should make sure to return a default info struct or some zero
> response buffer.

Yes, lets not implement an empty struct. The core should permit a
driver to nop this

Should I add this?

@@ -62,7 +62,11 @@ static int fwctl_cmd_info(struct fwctl_ucmd *ucmd)
        if (cmd->flags)
                return -EOPNOTSUPP;
 
-       if (cmd->device_data_len) {
+       if (!fwctl->ops->info && cmd->device_data_len) {
+               if (clear_user(u64_to_user_ptr(cmd->out_device_data),
+                              cmd->device_data_len))
+                       return -EFAULT;
+       } else if (cmd->device_data_len) {
                void *driver_info __free(kfree) =
                        fwctl->ops->info(ucmd->uctx, &driver_info_len);
                if (IS_ERR(driver_info))

Jason