STRUCT FC_EXCH(9)

okay so you opened struct fc_exch(9) from the Kernel API Manual, and it’s literally all about Fibre Channel Exchange — kernel struct edition, bestie. 💅✨

💅 NAME

struct fc_exch — Fibre Channel Exchange. That’s the name situation, periodt. 🎀

✨ SYNOPSIS

Here’s the struct in all its exact glory, no cap, because we do not mess with types around here:

       struct fc_exch {
           spinlock_t ex_lock;
           atomic_t ex_refcnt;
           enum fc_class       class;
           struct fc_exch_mgr  *em;
           struct fc_exch_pool *pool;
           struct list_head    ex_list;
           struct fc_lport     *lp;
           u32 esb_stat;
           u8 state;
           u8 fh_type;
           u8 seq_id;
           u8 encaps;
           u16 xid;
           u16 oxid;
           u16 rxid;
           u32 oid;
           u32 sid;
           u32 did;
           u32 r_a_tov;
           u32 f_ctl;
           struct fc_seq       seq;
           int resp_active;
           struct task_struct  *resp_task;
           wait_queue_head_t resp_wq;
           void (*resp)(struct fc_seq *, struct fc_frame *, void *);
           void *arg;
           void (*destructor)(struct fc_seq *, void *);
           struct delayed_work timeout_work;
        };

🫶 Members

okay bestie, member-by-member, no skips, no crumbs:

• ex_lock — Lock that protects the exchange. iconic protective energy. 🔒
• ex_refcnt — Reference count.
• class — The class of service.
• em — Exchange manager.
• pool — Exchange pool.
• ex_list — Handle used by the EM to track free exchanges.
• lp — The local port that this exchange is on.
• esb_stat — ESB exchange status.
• state — The exchange’s state.
• fh_type — The frame type.
• seq_id — The next sequence ID to use.
• encaps — encapsulation information for lower-level driver.
• xid — The exchange ID.
• oxid — Originator’s exchange ID.
• rxid — Responder’s exchange ID.
• oid — Originator’s FCID.
• sid — Source FCID.
• did — Destination FCID.
• r_a_tov — Resource allocation time out value (in msecs).
• f_ctl — F_CTL flags for the sequence.
• seq — The sequence in use on this exchange.
• resp_active — Number of tasks that are concurrently executing resp.
• resp_task — If resp_active > 0, either the task executing resp, the task that has been interrupted to execute the soft-IRQ executing resp, or NULL if more than one task is executing resp concurrently. yes, it’s a whole situation. 😭
• resp_wq — Waitqueue for the tasks waiting on resp_active.
• resp — Callback for responses on this exchange.
• arg — Passed as a void pointer to the resp callback.
• destructor — Called when destroying the exchange.
• timeout_work — Handle for timeout handler.

💖 Description

Locking notes, bestie: The ex_lock protects following items: state, esb_stat, f_ctl, seq.ssb_stat, seq_id, sequence allocation. That’s the list, and yes you should take it seriously. 💅🔥

🌈 SEE ALSO

Kernel file ./include/scsi/libfc.h — plus the whole friend group:

• enum fc_lport_state(9)
• enum fc_rport_state(9)
• struct fc_disc_port(9)
• enum fc_rport_event(9)
• struct fc_rport_operations(9)
• struct fc_rport_libfc_priv(9)
• struct fc_rport_priv(9)
• struct fc_stats(9)
• struct fc_seq_els_data(9)
• struct fc_fcp_pkt(9)
• struct fc_seq(9)
• struct fc_disc(9)
• struct fc_lport(9)
• struct fc4_prov(9)
• fc_lport_test_ready(9)
• fc_set_wwnn(9)
• fc_set_wwpn(9)
• fc_lport_state_enter(9)
• fc_lport_init_stats(9)
• fc_lport_free_stats(9)
• lport_priv(9)
• libfc_host_alloc(9)

That’s the page, bestie! Source/version ./include/scsi, dated October 2026, and it’s struct fc_exch(9) forever. 💖🎀🦋