scsi: target: Have drivers report if they support direct submissions

In some cases, like with multiple LUN targets or where the target has to
respond to transport level requests from the receiving context it can be
better to defer cmd submission to a helper thread. If the backend driver
blocks on something like request/tag allocation it can block the entire
target submission path and other LUs and transport IO on that session.

In other cases like single LUN targets with storage that can support all
the commands that the target can queue, then it's best to submit the cmd
to the backend from the target's cmd receiving context.

Subsequent commits will allow the user to config what they prefer, but
drivers like loop can't directly submit because they can be called from a
context that can't sleep. And, drivers like vhost-scsi can support direct
submission, but need to keep their default behavior of deferring execution
to avoid possible regressions where the backend can block.

Make the drivers tell LIO core if they support direct submissions and their
current default, so we can prevent users from misconfiguring the system and
initialize devices correctly.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://lore.kernel.org/r/20230928020907.5730-2-michael.christie@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/infiniband/ulp/srpt/ib_srpt.c

@@ -3867,6 +3867,9 @@ static const struct target_core_fabric_ops srpt_template = {
 	.tfc_discovery_attrs		= srpt_da_attrs,
 	.tfc_wwn_attrs			= srpt_wwn_attrs,
 	.tfc_tpg_attrib_attrs		= srpt_tpg_attrib_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 /**

drivers/scsi/elx/efct/efct_lio.c

@@ -1611,6 +1611,8 @@ static const struct target_core_fabric_ops efct_lio_ops = {
 	.sess_get_initiator_sid		= NULL,
 	.tfc_tpg_base_attrs		= efct_lio_tpg_attrs,
 	.tfc_tpg_attrib_attrs           = efct_lio_tpg_attrib_attrs,
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static const struct target_core_fabric_ops efct_lio_npiv_ops = {
@@ -1646,6 +1648,9 @@ static const struct target_core_fabric_ops efct_lio_npiv_ops = {
 	.sess_get_initiator_sid		= NULL,
 	.tfc_tpg_base_attrs		= efct_lio_npiv_tpg_attrs,
 	.tfc_tpg_attrib_attrs		= efct_lio_npiv_tpg_attrib_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 int efct_scsi_tgt_driver_init(void)

drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c

@@ -3975,6 +3975,9 @@ static const struct target_core_fabric_ops ibmvscsis_ops = {
 	.fabric_drop_tpg		= ibmvscsis_drop_tpg,
 
 	.tfc_wwn_attrs			= ibmvscsis_wwn_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static void ibmvscsis_dev_release(struct device *dev) {};

drivers/scsi/qla2xxx/tcm_qla2xxx.c

@@ -1822,6 +1822,9 @@ static const struct target_core_fabric_ops tcm_qla2xxx_ops = {
 	.tfc_wwn_attrs			= tcm_qla2xxx_wwn_attrs,
 	.tfc_tpg_base_attrs		= tcm_qla2xxx_tpg_attrs,
 	.tfc_tpg_attrib_attrs		= tcm_qla2xxx_tpg_attrib_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static const struct target_core_fabric_ops tcm_qla2xxx_npiv_ops = {
@@ -1859,6 +1862,9 @@ static const struct target_core_fabric_ops tcm_qla2xxx_npiv_ops = {
 	.fabric_init_nodeacl		= tcm_qla2xxx_init_nodeacl,
 
 	.tfc_wwn_attrs			= tcm_qla2xxx_wwn_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static int tcm_qla2xxx_register_configfs(void)

drivers/target/iscsi/iscsi_target_configfs.c

@@ -1590,4 +1590,7 @@ const struct target_core_fabric_ops iscsi_ops = {
 	.tfc_tpg_nacl_param_attrs	= lio_target_nacl_param_attrs,
 
 	.write_pending_must_be_called	= 1,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };

drivers/target/loopback/tcm_loop.c

@@ -1102,6 +1102,8 @@ static const struct target_core_fabric_ops loop_ops = {
 	.tfc_wwn_attrs			= tcm_loop_wwn_attrs,
 	.tfc_tpg_base_attrs		= tcm_loop_tpg_attrs,
 	.tfc_tpg_attrib_attrs		= tcm_loop_tpg_attrib_attrs,
+	.default_submit_type		= TARGET_QUEUE_SUBMIT,
+	.direct_submit_supp		= 0,
 };
 
 static int __init tcm_loop_fabric_init(void)

drivers/target/sbp/sbp_target.c

@@ -2278,6 +2278,9 @@ static const struct target_core_fabric_ops sbp_ops = {
 	.tfc_wwn_attrs			= sbp_wwn_attrs,
 	.tfc_tpg_base_attrs		= sbp_tpg_base_attrs,
 	.tfc_tpg_attrib_attrs		= sbp_tpg_attrib_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static int __init sbp_init(void)

drivers/target/tcm_fc/tfc_conf.c

@@ -432,6 +432,9 @@ static const struct target_core_fabric_ops ft_fabric_ops = {
 
 	.tfc_wwn_attrs			= ft_wwn_attrs,
 	.tfc_tpg_nacl_base_attrs	= ft_nacl_base_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static struct notifier_block ft_notifier = {

drivers/usb/gadget/function/f_tcm.c

@@ -1687,6 +1687,9 @@ static const struct target_core_fabric_ops usbg_ops = {
 
 	.tfc_wwn_attrs			= usbg_wwn_attrs,
 	.tfc_tpg_base_attrs		= usbg_base_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 /* Start gadget.c code */

drivers/vhost/scsi.c

@@ -2598,6 +2598,9 @@ static const struct target_core_fabric_ops vhost_scsi_ops = {
 	.tfc_wwn_attrs			= vhost_scsi_wwn_attrs,
 	.tfc_tpg_base_attrs		= vhost_scsi_tpg_attrs,
 	.tfc_tpg_attrib_attrs		= vhost_scsi_tpg_attrib_attrs,
+
+	.default_submit_type		= TARGET_QUEUE_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static int __init vhost_scsi_init(void)

drivers/xen/xen-scsiback.c

@@ -1832,6 +1832,9 @@ static const struct target_core_fabric_ops scsiback_ops = {
 	.tfc_wwn_attrs			= scsiback_wwn_attrs,
 	.tfc_tpg_base_attrs		= scsiback_tpg_attrs,
 	.tfc_tpg_param_attrs		= scsiback_param_attrs,
+
+	.default_submit_type		= TARGET_DIRECT_SUBMIT,
+	.direct_submit_supp		= 1,
 };
 
 static const struct xenbus_device_id scsiback_ids[] = {

include/target/target_core_base.h

@@ -108,6 +108,15 @@
 #define SE_MODE_PAGE_BUF			512
 #define SE_SENSE_BUF				96
 
+enum target_submit_type {
+	/* Use the fabric driver's default submission type */
+	TARGET_FABRIC_DEFAULT_SUBMIT,
+	/* Submit from the calling context */
+	TARGET_DIRECT_SUBMIT,
+	/* Defer submission to the LIO workqueue */
+	TARGET_QUEUE_SUBMIT,
+};
+
 /* struct se_hba->hba_flags */
 enum hba_flags_table {
 	HBA_FLAGS_INTERNAL_USE	= 0x01,

include/target/target_core_fabric.h

@@ -118,6 +118,15 @@ struct target_core_fabric_ops {
 	 * its entirety before a command is aborted.
 	 */
 	unsigned int write_pending_must_be_called:1;
+	/*
+	 * Set this if the driver supports submitting commands to the backend
+	 * from target_submit/target_submit_cmd.
+	 */
+	unsigned int direct_submit_supp:1;
+	/*
+	 * Set this to a target_submit_type value.
+	 */
+	u8 default_submit_type;
 };
 
 int target_register_template(const struct target_core_fabric_ops *fo);