usb: f_mass_storage: limit number of reported LUNs

Mass storage function created via configfs always reports eight LUNs
to the hosts even if only one LUN has been configured. Adjust the
number when the USB function is allocated based on LUNs that user
has created.

Cc: <[e-mail]>
Tested-by: Gregory CLEMENT <[e-mail]>
Signed-off-by: Michal Nazarewicz <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/function/f_mass_storage.c

···
 		return -EINVAL;
 	}
 
-	curlun = kcalloc(nluns, sizeof(*curlun), GFP_KERNEL);
+	curlun = kcalloc(FSG_MAX_LUNS, sizeof(*curlun), GFP_KERNEL);
 	if (unlikely(!curlun))
 		return -ENOMEM;
 
···
 
 	common->luns = curlun;
 	common->nluns = nluns;
-
-	pr_info("Number of LUNs=%d\n", common->nluns);
 
 	return 0;
 }
···
 	struct fsg_opts *opts = fsg_opts_from_func_inst(fi);
 	struct fsg_common *common = opts->common;
 	struct fsg_dev *fsg;
+	unsigned nluns, i;
 
 	fsg = kzalloc(sizeof(*fsg), GFP_KERNEL);
 	if (unlikely(!fsg))
 		return ERR_PTR(-ENOMEM);
 
 	mutex_lock(&opts->lock);
+	if (!opts->refcnt) {
+		for (nluns = i = 0; i < FSG_MAX_LUNS; ++i)
+			if (common->luns[i])
+				nluns = i + 1;
+		if (!nluns)
+			pr_warn("No LUNS defined, continuing anyway\n");
+		else
+			common->nluns = nluns;
+		pr_info("Number of LUNs=%u\n", common->nluns);
+	}
 	opts->refcnt++;
 	mutex_unlock(&opts->lock);
+
 	fsg->function.name	= FSG_DRIVER_DESC;
 	fsg->function.bind	= fsg_bind;
 	fsg->function.unbind	= fsg_unbind;