target: Add SCF_EMULATE_QUEUE_FULL -> transport_handle_queue_full

This patch adds SCF_EMULATE_QUEUE_FULL support using -EAGAIN failures
via transport_handle_queue_full() to signal queue full in completion
path TFO->queue_data_in() and TFO->queue_status() callbacks.

This is done using a new se_cmd->transport_qf_callback() to handle
the following queue full exception cases within target core:

*) TRANSPORT_COMPLETE_OK (for completion path queue full)

*) TRANSPORT_COMPLETE_QF_WP (for TRANSPORT_WRITE_PENDING queue full)

*) transport_send_check_condition_and_sense() failure paths in
   transport_generic_request_failure() and transport_generic_complete_ok()

All logic is driven using se_device->qf_work_queue -> target_qf_do_work()
to to requeue outstanding se_cmd at the head of se_dev->queue_obj->qobj_list
for transport_processing_thread() execution.

Tested using tcm_qla2xxx with MAX_OUTSTANDING_COMMANDS=128 for FCP READ
to trigger the TRANSPORT_COMPLETE_OK queue full cases, and a simulated
TFO->write_pending() -EAGAIN failure to trigger TRANSPORT_COMPLETE_QF_WP.

Reported-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 71abc4c5e2b4..cd163dd94cd4 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -99,6 +99,7 @@ enum transport_state_table {
         TRANSPORT_FREE          = 15,
         TRANSPORT_NEW_CMD_MAP   = 16,
         TRANSPORT_FREE_CMD_INTR = 17,
+        TRANSPORT_COMPLETE_QF_WP = 18,
 };
 
 /* Used for struct se_cmd->se_cmd_flags */
@@ -125,6 +126,7 @@ enum se_cmd_flags_table {
         SCF_PASSTHROUGH_CONTIG_TO_SG    = 0x00200000,
         SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC = 0x00400000,
         SCF_EMULATE_CDB_ASYNC           = 0x01000000,
+        SCF_EMULATE_QUEUE_FULL          = 0x02000000,
 };
 
 /* struct se_dev_entry->lun_flags and struct se_lun->lun_access */
@@ -466,6 +468,7 @@ struct se_cmd {
         struct list_head        se_delayed_node;
         struct list_head        se_ordered_node;
         struct list_head        se_lun_node;
+        struct list_head        se_qf_node;
         struct se_device      *se_dev;
         struct se_dev_entry   *se_deve;
         struct se_device        *se_obj_ptr;
@@ -480,6 +483,8 @@ struct se_cmd {
         void (*transport_split_cdb)(unsigned long long, u32 *, unsigned char *);
         void (*transport_wait_for_tasks)(struct se_cmd *, int, int);
         void (*transport_complete_callback)(struct se_cmd *);
+        int (*transport_qf_callback)(struct se_cmd *);
+
         unsigned char           *t_task_cdb;
         unsigned char           __t_task_cdb[TCM_MAX_COMMAND_SIZE];
         unsigned long long      t_task_lba;
@@ -743,6 +748,7 @@ struct se_device {
         atomic_t                dev_status_thr_count;
         atomic_t                dev_hoq_count;
         atomic_t                dev_ordered_sync;
+        atomic_t                dev_qf_count;
         struct se_obj           dev_obj;
         struct se_obj           dev_access_obj;
         struct se_obj           dev_export_obj;
@@ -758,6 +764,7 @@ struct se_device {
         spinlock_t              dev_status_thr_lock;
         spinlock_t              se_port_lock;
         spinlock_t              se_tmr_lock;
+        spinlock_t              qf_cmd_lock;
         /* Used for legacy SPC-2 reservationsa */
         struct se_node_acl      *dev_reserved_node_acl;
         /* Used for ALUA Logical Unit Group membership */
@@ -771,10 +778,12 @@ struct se_device {
         struct task_struct      *process_thread;
         pid_t                   process_thread_pid;
         struct task_struct              *dev_mgmt_thread;
+        struct work_struct      qf_work_queue;
         struct list_head        delayed_cmd_list;
         struct list_head        ordered_cmd_list;
         struct list_head        execute_task_list;
         struct list_head        state_task_list;
+        struct list_head        qf_cmd_list;
         /* Pointer to associated SE HBA */
         struct se_hba           *se_hba;
         struct se_subsystem_dev *se_sub_dev;