nvmet: fix per feat data len for get_feature

The existing implementation for the get_feature admin-cmd does not
use per-feature data len. This patch introduces a new helper function
nvmet_feat_data_len(), which is used to calculate per feature data len.
Right now we only set data len for fid 0x81 (NVME_FEAT_HOST_ID).

Fixes: commit e9061c397839 ("nvmet: Remove the data_len field from the nvmet_req struct")

Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Amit Engel <[e-mail]>
[endiness, naming, and kernel style fixes]
Signed-off-by: Chaitanya Kulkarni <[e-mail]>
Signed-off-by: Keith Busch <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/nvme/target/admin-cmd.c

···
 	return len;
 }
 
+static u32 nvmet_feat_data_len(struct nvmet_req *req, u32 cdw10)
+{
+	switch (cdw10 & 0xff) {
+	case NVME_FEAT_HOST_ID:
+		return sizeof(req->sq->ctrl->hostid);
+	default:
+		return 0;
+	}
+}
+
 u64 nvmet_get_log_page_offset(struct nvme_command *cmd)
 {
 	return le64_to_cpu(cmd->get_log_page.lpo);
···
 	u32 cdw10 = le32_to_cpu(req->cmd->common.cdw10);
 	u16 status = 0;
 
-	if (!nvmet_check_data_len(req, 0))
+	if (!nvmet_check_data_len(req, nvmet_feat_data_len(req, cdw10)))
 		return;
 
 	switch (cdw10 & 0xff) {