target and iSCSI Interfaces Guide¶

Introduction and Overview¶

TBD

Target core device interfaces¶

This section is blank because no kerneldoc comments have been added to drivers/target/target_core_device.c.

Target core transport interfaces¶

int transport_init_session(struct se_session *se_sess)¶: initialize a session object

Parameters

struct se_session *se_sess: Session object pointer.

Description

The caller must have zero-initialized se_sess before calling this function.

struct se_session *transport_alloc_session(enum target_prot_op sup_prot_ops)¶: allocate a session object and initialize it

Parameters

enum target_prot_op sup_prot_ops: bitmask that defines which T10-PI modes are supported.

int transport_alloc_session_tags(struct se_session *se_sess, unsigned int tag_num, unsigned int tag_size)¶: allocate target driver private data

Parameters

struct se_session *se_sess: Session pointer.
unsigned int tag_num: Maximum number of in-flight commands between initiator and target.
unsigned int tag_size: Size in bytes of the private data a target driver associates with each command.

int target_init_cmd(struct se_cmd *se_cmd, struct se_session *se_sess, unsigned char *sense, u64 unpacked_lun, u32 data_length, int task_attr, int data_dir, int flags)¶: initialize se_cmd

Parameters

struct se_cmd *se_cmd: command descriptor to init
struct se_session *se_sess: associated se_sess for endpoint
unsigned char *sense: pointer to SCSI sense buffer
u64 unpacked_lun: unpacked LUN to reference for struct se_lun
u32 data_length: fabric expected data transfer length
int task_attr: SAM task attribute
int data_dir: DMA data direction
int flags: flags for command submission from target_sc_flags_tables

Description

Task tags are supported if the caller has set se_cmd->tag.

If the fabric driver calls target_stop_session, then it must check the return code and handle failures. This will never fail for other drivers, and the return code can be ignored.

Return

less than zero to signal active I/O shutdown failure.

zero on success.

int target_submit_prep(struct se_cmd *se_cmd, unsigned char *cdb, struct scatterlist *sgl, u32 sgl_count, struct scatterlist *sgl_bidi, u32 sgl_bidi_count, struct scatterlist *sgl_prot, u32 sgl_prot_count, gfp_t gfp)¶: prepare cmd for submission

Parameters

struct se_cmd *se_cmd: command descriptor to prep
unsigned char *cdb: pointer to SCSI CDB
struct scatterlist *sgl: struct scatterlist memory for unidirectional mapping
u32 sgl_count: scatterlist count for unidirectional mapping
struct scatterlist *sgl_bidi: struct scatterlist memory for bidirectional READ mapping
u32 sgl_bidi_count: scatterlist count for bidirectional READ mapping
struct scatterlist *sgl_prot: struct scatterlist memory protection information
u32 sgl_prot_count: scatterlist count for protection information
gfp_t gfp: gfp allocation type

Return

less than zero to signal failure.

zero on success.

Description

If failure is returned, lio will the callers queue_status to complete the cmd.

void target_submit(struct se_cmd *se_cmd)¶: perform final initialization and submit cmd to LIO core

Parameters

struct se_cmd *se_cmd: command descriptor to submit

Description

target_submit_prep must have been called on the cmd, and this must be called from process context.

void target_submit_cmd(struct se_cmd *se_cmd, struct se_session *se_sess, unsigned char *cdb, unsigned char *sense, u64 unpacked_lun, u32 data_length, int task_attr, int data_dir, int flags)¶: lookup unpacked lun and submit uninitialized se_cmd

Parameters

struct se_cmd *se_cmd: command descriptor to submit
struct se_session *se_sess: associated se_sess for endpoint
unsigned char *cdb: pointer to SCSI CDB
unsigned char *sense: pointer to SCSI sense buffer
u64 unpacked_lun: unpacked LUN to reference for struct se_lun
u32 data_length: fabric expected data transfer length
int task_attr: SAM task attribute
int data_dir: DMA data direction
int flags: flags for command submission from target_sc_flags_tables

Description

Task tags are supported if the caller has set se_cmd->tag.

This may only be called from process context, and also currently assumes internal allocation of fabric payload buffer by target-core.

It also assumes interal target core SGL memory allocation.

This function must only be used by drivers that do their own sync during shutdown and does not use target_stop_session. If there is a failure this function will call into the fabric driver’s queue_status with a CHECK_CONDITION.

void target_queue_submission(struct se_cmd *se_cmd)¶: queue the cmd to run on the LIO workqueue

Parameters

struct se_cmd *se_cmd: command descriptor to submit

int target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess, unsigned char *sense, u64 unpacked_lun, void *fabric_tmr_ptr, unsigned char tm_type, gfp_t gfp, u64 tag, int flags)¶: lookup unpacked lun and submit uninitialized se_cmd for TMR CDBs

Parameters

struct se_cmd *se_cmd: command descriptor to submit
struct se_session *se_sess: associated se_sess for endpoint
unsigned char *sense: pointer to SCSI sense buffer
u64 unpacked_lun: unpacked LUN to reference for struct se_lun
void *fabric_tmr_ptr: fabric context for TMR req
unsigned char tm_type: Type of TM request
gfp_t gfp: gfp type for caller
u64 tag: referenced task tag for TMR_ABORT_TASK
int flags: submit cmd flags

Description

Callable from all contexts.

int target_get_sess_cmd(struct se_cmd *se_cmd, bool ack_kref)¶: Verify the session is accepting cmds and take ref

Parameters

struct se_cmd *se_cmd: command descriptor to add
bool ack_kref: Signal that fabric will perform an ack target_put_sess_cmd()

int target_put_sess_cmd(struct se_cmd *se_cmd)¶: decrease the command reference count

Parameters

struct se_cmd *se_cmd: command to drop a reference from

Description

Returns 1 if and only if this target_put_sess_cmd() call caused the refcount to drop to zero. Returns zero otherwise.

void target_stop_session(struct se_session *se_sess)¶: Stop new IO from being queued on the session.

Parameters

struct se_session *se_sess: session to stop

void target_wait_for_sess_cmds(struct se_session *se_sess)¶: Wait for outstanding commands

Parameters

struct se_session *se_sess: session to wait for active I/O

bool transport_wait_for_tasks(struct se_cmd *cmd)¶: set CMD_T_STOP and wait for t_transport_stop_comp

Parameters

struct se_cmd *cmd: command to wait on

int target_send_busy(struct se_cmd *cmd)¶: Send SCSI BUSY status back to the initiator

Parameters

struct se_cmd *cmd: SCSI command for which to send a BUSY reply.

Note

Only call this function if target_submit_cmd*() failed.

Target-supported userspace I/O¶

Userspace I/O¶

Define a shared-memory interface for LIO to pass SCSI commands and data to userspace for processing. This is to allow backends that are too complex for in-kernel support to be possible.

It uses the UIO framework to do a lot of the device-creation and introspection work for us.

See the .h file for how the ring is laid out. Note that while the command ring is defined, the particulars of the data area are not. Offset values in the command entry point to other locations internal to the mmap-ed area. There is separate space outside the command ring for data buffers. This leaves maximum flexibility for moving buffer allocations, or even page flipping or other allocation techniques, without altering the command ring layout.

SECURITY: The user process must be assumed to be malicious. There’s no way to prevent it breaking the command ring protocol if it wants, but in order to prevent other issues we must only ever read data from the shared memory area, not offsets or sizes. This applies to command ring entries as well as the mailbox. Extra code needed for this may have a ‘UAM’ comment.

Ring Design¶

The mmaped area is divided into three parts: 1) The mailbox (struct tcmu_mailbox, below); 2) The command ring; 3) Everything beyond the command ring (data).

The mailbox tells userspace the offset of the command ring from the start of the shared memory region, and how big the command ring is.

The kernel passes SCSI commands to userspace by putting a struct tcmu_cmd_entry in the ring, updating mailbox->cmd_head, and poking userspace via UIO’s interrupt mechanism.

tcmu_cmd_entry contains a header. If the header type is PAD, userspace should skip hdr->length bytes (mod cmdr_size) to find the next cmd_entry.

Otherwise, the entry will contain offsets into the mmaped area that contain the cdb and data buffers – the latter accessible via the iov array. iov addresses are also offsets into the shared area.

When userspace is completed handling the command, set entry->rsp.scsi_status, fill in rsp.sense_buffer if appropriate, and also set mailbox->cmd_tail equal to the old cmd_tail plus hdr->length, mod cmdr_size. If cmd_tail doesn’t equal cmd_head, it should process the next packet the same way, and so on.

iSCSI helper functions¶

void iscsi_prep_data_out_pdu(struct iscsi_task *task, struct iscsi_r2t_info *r2t, struct iscsi_data *hdr)¶: initialize Data-Out

Parameters

struct iscsi_task *task: scsi command task
struct iscsi_r2t_info *r2t: R2T info
struct iscsi_data *hdr: iscsi data in pdu

Notes

Initialize Data-Out within this R2T sequence and finds proper data_offset within this SCSI command.

This function is called with connection lock taken.

void iscsi_complete_scsi_task(struct iscsi_task *task, uint32_t exp_cmdsn, uint32_t max_cmdsn)¶: finish scsi task normally

Parameters

struct iscsi_task *task: iscsi task for scsi cmd
uint32_t exp_cmdsn: expected cmd sn in cpu format
uint32_t max_cmdsn: max cmd sn in cpu format

Description

This is used when drivers do not need or cannot perform lower level pdu processing.

Called with session back_lock

struct iscsi_task *iscsi_itt_to_task(struct iscsi_conn *conn, itt_t itt)¶: look up task by itt

Parameters

struct iscsi_conn *conn: iscsi connection
itt_t itt: itt

Description

This should be used for mgmt tasks like login and nops, or if the LDD’s itt space does not include the session age.

The session back_lock must be held.

int __iscsi_complete_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr, char *data, int datalen)¶: complete pdu

Parameters

struct iscsi_conn *conn: iscsi conn
struct iscsi_hdr *hdr: iscsi header
char *data: data buffer
int datalen: len of data buffer

Description

Completes pdu processing by freeing any resources allocated at queuecommand or send generic. session back_lock must be held and verify itt must have been called.

struct iscsi_task *iscsi_itt_to_ctask(struct iscsi_conn *conn, itt_t itt)¶: look up ctask by itt

Parameters

struct iscsi_conn *conn: iscsi connection
itt_t itt: itt

Description

This should be used for cmd tasks.

The session back_lock must be held.

void iscsi_requeue_task(struct iscsi_task *task)¶: requeue task to run from session workqueue

Parameters

struct iscsi_task *task: task to requeue

Description

Callers must have taken a ref to the task that is going to be requeued.

void iscsi_suspend_queue(struct iscsi_conn *conn)¶: suspend iscsi_queuecommand

Parameters

struct iscsi_conn *conn: iscsi conn to stop queueing IO on

Description

This grabs the session frwd_lock to make sure no one is in xmit_task/queuecommand, and then sets suspend to prevent new commands from being queued. This only needs to be called by offload drivers that need to sync a path like ep disconnect with the iscsi_queuecommand/xmit_task. To start IO again libiscsi will call iscsi_start_tx and iscsi_unblock_session when in FFP.

void iscsi_suspend_tx(struct iscsi_conn *conn)¶: suspend iscsi_data_xmit

Parameters

struct iscsi_conn *conn: iscsi conn tp stop processing IO on.

Description

This function sets the suspend bit to prevent iscsi_data_xmit from sending new IO, and if work is queued on the xmit thread it will wait for it to be completed.

void iscsi_conn_unbind(struct iscsi_cls_conn *cls_conn, bool is_active)¶: prevent queueing to conn.

Parameters

struct iscsi_cls_conn *cls_conn: iscsi conn ep is bound to.
bool is_active: is the conn in use for boot or is this for EH/termination

Description

This must be called by drivers implementing the ep_disconnect callout. It disables queueing to the connection from libiscsi in preparation for an ep_disconnect call.

int iscsi_eh_session_reset(struct scsi_cmnd *sc)¶: drop session and attempt relogin

Parameters

struct scsi_cmnd *sc: scsi command

Description

This function will wait for a relogin, session termination from userspace, or a recovery/replacement timeout.

int iscsi_eh_recover_target(struct scsi_cmnd *sc)¶: reset target and possibly the session

Parameters

struct scsi_cmnd *sc: scsi command

Description

This will attempt to send a warm target reset. If that fails, we will escalate to ERL0 session recovery.

int iscsi_host_add(struct Scsi_Host *shost, struct device *pdev)¶: add host to system

Parameters

struct Scsi_Host *shost: scsi host
struct device *pdev: parent device

Description

This should be called by partial offload and software iscsi drivers to add a host to the system.

struct Scsi_Host *iscsi_host_alloc(struct scsi_host_template *sht, int dd_data_size, bool xmit_can_sleep)¶: allocate a host and driver data

Parameters

struct scsi_host_template *sht: scsi host template
int dd_data_size: driver host data size
bool xmit_can_sleep: bool indicating if LLD will queue IO from a work queue

Description

This should be called by partial offload and software iscsi drivers. To access the driver specific memory use the iscsi_host_priv() macro.

void iscsi_host_remove(struct Scsi_Host *shost)¶: remove host and sessions

Parameters

struct Scsi_Host *shost: scsi host

Description

If there are any sessions left, this will initiate the removal and wait for the completion.

struct iscsi_cls_session *iscsi_session_setup(struct iscsi_transport *iscsit, struct Scsi_Host *shost, uint16_t cmds_max, int dd_size, int cmd_task_size, uint32_t initial_cmdsn, unsigned int id)¶: create iscsi cls session and host and session

Parameters

struct iscsi_transport *iscsit: iscsi transport template
struct Scsi_Host *shost: scsi host
uint16_t cmds_max: session can queue
int dd_size: private driver data size, added to session allocation size
int cmd_task_size: LLD task private data size
uint32_t initial_cmdsn: initial CmdSN
unsigned int id: target ID to add to this session

Description

This can be used by software iscsi_transports that allocate a session per scsi host.

Callers should set cmds_max to the largest total numer (mgmt + scsi) of tasks they support. The iscsi layer reserves ISCSI_MGMT_CMDS_MAX tasks for nop handling and login/logout requests.

void iscsi_session_teardown(struct iscsi_cls_session *cls_session)¶: destroy session, host, and cls_session

Parameters

struct iscsi_cls_session *cls_session: iscsi session

struct iscsi_cls_conn *iscsi_conn_setup(struct iscsi_cls_session *cls_session, int dd_size, uint32_t conn_idx)¶: create iscsi_cls_conn and iscsi_conn

Parameters

struct iscsi_cls_session *cls_session: iscsi_cls_session
int dd_size: private driver data size
uint32_t conn_idx: cid

void iscsi_conn_teardown(struct iscsi_cls_conn *cls_conn)¶: teardown iscsi connection

Parameters

struct iscsi_cls_conn *cls_conn: iscsi class connection

Description

TODO: we may need to make this into a two step process like scsi-mls remove + put host

iSCSI boot information¶

struct iscsi_boot_kobj *iscsi_boot_create_target(struct iscsi_boot_kset *boot_kset, int index, void *data, ssize_t (*show)(void *data, int type, char *buf), umode_t (*is_visible)(void *data, int type), void (*release)(void *data))¶: create boot target sysfs dir

Parameters

struct iscsi_boot_kset *boot_kset: boot kset
int index: the target id
void *data: driver specific data for target
ssize_t (*show) (void *data, int type, char *buf): attr show function
umode_t (*is_visible) (void *data, int type): attr visibility function
void (*release) (void *data): release function

Note

The boot sysfs lib will free the data passed in for the caller when all refs to the target kobject have been released.

struct iscsi_boot_kobj *iscsi_boot_create_initiator(struct iscsi_boot_kset *boot_kset, int index, void *data, ssize_t (*show)(void *data, int type, char *buf), umode_t (*is_visible)(void *data, int type), void (*release)(void *data))¶: create boot initiator sysfs dir

Parameters

struct iscsi_boot_kset *boot_kset: boot kset
int index: the initiator id
void *data: driver specific data
ssize_t (*show) (void *data, int type, char *buf): attr show function
umode_t (*is_visible) (void *data, int type): attr visibility function
void (*release) (void *data): release function

Note

The boot sysfs lib will free the data passed in for the caller when all refs to the initiator kobject have been released.

struct iscsi_boot_kobj *iscsi_boot_create_ethernet(struct iscsi_boot_kset *boot_kset, int index, void *data, ssize_t (*show)(void *data, int type, char *buf), umode_t (*is_visible)(void *data, int type), void (*release)(void *data))¶: create boot ethernet sysfs dir

Parameters

struct iscsi_boot_kset *boot_kset: boot kset
int index: the ethernet device id
void *data: driver specific data
ssize_t (*show) (void *data, int type, char *buf): attr show function
umode_t (*is_visible) (void *data, int type): attr visibility function
void (*release) (void *data): release function

Note

The boot sysfs lib will free the data passed in for the caller when all refs to the ethernet kobject have been released.

struct iscsi_boot_kobj *iscsi_boot_create_acpitbl(struct iscsi_boot_kset *boot_kset, int index, void *data, ssize_t (*show)(void *data, int type, char *buf), umode_t (*is_visible)(void *data, int type), void (*release)(void *data))¶: create boot acpi table sysfs dir

Parameters

struct iscsi_boot_kset *boot_kset: boot kset
int index: not used
void *data: driver specific data
ssize_t (*show)(void *data, int type, char *buf): attr show function
umode_t (*is_visible)(void *data, int type): attr visibility function
void (*release)(void *data): release function

Note

The boot sysfs lib will free the data passed in for the caller when all refs to the acpitbl kobject have been released.

struct iscsi_boot_kset *iscsi_boot_create_kset(const char *set_name)¶: creates root sysfs tree

Parameters

const char *set_name: name of root dir

struct iscsi_boot_kset *iscsi_boot_create_host_kset(unsigned int hostno)¶: creates root sysfs tree for a scsi host

Parameters

unsigned int hostno: host number of scsi host

void iscsi_boot_destroy_kset(struct iscsi_boot_kset *boot_kset)¶: destroy kset and kobjects under it

Parameters

struct iscsi_boot_kset *boot_kset: boot kset

Description

This will remove the kset and kobjects and attrs under it.

iSCSI TCP interfaces¶

int iscsi_sw_tcp_recv(read_descriptor_t *rd_desc, struct sk_buff *skb, unsigned int offset, size_t len)¶: TCP receive in sendfile fashion

Parameters

read_descriptor_t *rd_desc: read descriptor
struct sk_buff *skb: socket buffer
unsigned int offset: offset in skb
size_t len: skb->len - offset

int iscsi_sw_sk_state_check(struct sock *sk)¶: check socket state

Parameters

struct sock *sk: socket

Description

If the socket is in CLOSE or CLOSE_WAIT we should not close the connection if there is still some data pending.

Must be called with sk_callback_lock.

void iscsi_sw_tcp_write_space(struct sock *sk)¶: Called when more output buffer space is available

Parameters

struct sock *sk: socket space is available for

int iscsi_sw_tcp_xmit_segment(struct iscsi_tcp_conn *tcp_conn, struct iscsi_segment *segment)¶: transmit segment

Parameters

struct iscsi_tcp_conn *tcp_conn: the iSCSI TCP connection
struct iscsi_segment *segment: the buffer to transmnit

Description

This function transmits as much of the buffer as the network layer will accept, and returns the number of bytes transmitted.

If CRC hashing is enabled, the function will compute the hash as it goes. When the entire segment has been transmitted, it will retrieve the hash value and send it as well.

int iscsi_sw_tcp_xmit(struct iscsi_conn *conn)¶: TCP transmit

Parameters

struct iscsi_conn *conn: iscsi connection

int iscsi_sw_tcp_xmit_qlen(struct iscsi_conn *conn)¶: return the number of bytes queued for xmit

Parameters

struct iscsi_conn *conn: iscsi connection

int iscsi_tcp_segment_done(struct iscsi_tcp_conn *tcp_conn, struct iscsi_segment *segment, int recv, unsigned copied)¶: check whether the segment is complete

Parameters

struct iscsi_tcp_conn *tcp_conn: iscsi tcp connection
struct iscsi_segment *segment: iscsi segment to check
int recv: set to one of this is called from the recv path
unsigned copied: number of bytes copied

Description

Check if we’re done receiving this segment. If the receive buffer is full but we expect more data, move on to the next entry in the scatterlist.

If the amount of data we received isn’t a multiple of 4, we will transparently receive the pad bytes, too.

This function must be re-entrant.

void iscsi_tcp_hdr_recv_prep(struct iscsi_tcp_conn *tcp_conn)¶: prep segment for hdr reception

Parameters

struct iscsi_tcp_conn *tcp_conn: iscsi connection to prep for

Description

This function always passes NULL for the hash argument, because when this function is called we do not yet know the final size of the header and want to delay the digest processing until we know that.

void iscsi_tcp_cleanup_task(struct iscsi_task *task)¶: free tcp_task resources

Parameters

struct iscsi_task *task: iscsi task

Description

must be called with session back_lock

int iscsi_tcp_recv_segment_is_hdr(struct iscsi_tcp_conn *tcp_conn)¶: tests if we are reading in a header

Parameters

struct iscsi_tcp_conn *tcp_conn: iscsi tcp conn

Description

returns non zero if we are currently processing or setup to process a header.

int iscsi_tcp_recv_skb(struct iscsi_conn *conn, struct sk_buff *skb, unsigned int offset, bool offloaded, int *status)¶: Process skb

Parameters

struct iscsi_conn *conn: iscsi connection
struct sk_buff *skb: network buffer with header and/or data segment
unsigned int offset: offset in skb
bool offloaded: bool indicating if transfer was offloaded
int *status: iscsi TCP status result

Description

Will return status of transfer in status. And will return number of bytes copied.

int iscsi_tcp_task_init(struct iscsi_task *task)¶: Initialize iSCSI SCSI_READ or SCSI_WRITE commands

Parameters

struct iscsi_task *task: scsi command task

int iscsi_tcp_task_xmit(struct iscsi_task *task)¶: xmit normal PDU task

Parameters

struct iscsi_task *task: iscsi command task

Description

We’re expected to return 0 when everything was transmitted successfully, -EAGAIN if there’s still data in the queue, or != 0 for any other kind of error.