scsi: nvme-fc: Add new routine nvme_fc_io_getuuid()

Add nvme_fc_io_getuuid() to the nvme-fc transport. The routine is invoked
by the FC LLDD on a per-I/O request basis. The routine translates from the
FC-specific request structure to the bio and the cgroup structure in order
to obtain the FC appid stored in the cgroup structure. If a value is not
set or a bio is not found, a NULL appid (aka uuid) will be returned to the
LLDD.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Hannes Reinecke <[e-mail]>
Reviewed-by: Himanshu Madhani <[e-mail]>
Acked-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Muneendra Kumar <[e-mail]>
Signed-off-by: James Smart <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/nvme/host/fc.c

···
 	nvme_fc_error_recovery(ctrl, "transport detected io error");
 }
 
+/*
+ * nvme_fc_io_getuuid - Routine called to get the appid field
+ * associated with request by the lldd
+ * @req:IO request from nvme fc to driver
+ * Returns: UUID if there is an appid associated with VM or
+ * NULL if the user/libvirt has not set the appid to VM
+ */
+char *nvme_fc_io_getuuid(struct nvmefc_fcp_req *req)
+{
+	struct nvme_fc_fcp_op *op = fcp_req_to_fcp_op(req);
+	struct request *rq = op->rq;
+
+	if (!IS_ENABLED(CONFIG_BLK_CGROUP_FC_APPID) || !rq->bio)
+		return NULL;
+	return blkcg_get_fc_appid(rq->bio);
+}
+EXPORT_SYMBOL_GPL(nvme_fc_io_getuuid);
+
 static void
 nvme_fc_fcpio_done(struct nvmefc_fcp_req *req)
 {

include/linux/nvme-fc-driver.h

···
 			void *lsreqbuf, u32 lsreqbuf_len);
 
 
+/*
+ * Routine called to get the appid field associated with request by the lldd
+ *
+ * If the return value is NULL : the user/libvirt has not set the appid to VM
+ * If the return value is non-zero: Returns the appid associated with VM
+ *
+ * @req: IO request from nvme fc to driver
+ */
+char *nvme_fc_io_getuuid(struct nvmefc_fcp_req *req);
 
 /*
  * ***************  LLDD FC-NVME Target/Subsystem API ***************
···
 
 void nvmet_fc_rcv_fcp_abort(struct nvmet_fc_target_port *tgtport,
 			struct nvmefc_tgt_fcp_req *fcpreq);
+/*
+ * add a define, visible to the compiler, that indicates support
+ * for feature. Allows for conditional compilation in LLDDs.
+ */
+#define NVME_FC_FEAT_UUID	0x0001
 
 #endif /* _NVME_FC_DRIVER_H */