sysfs_ctlreg_write(9)

sysfs_ctlreg_write(9) 💅

okay so this is straight out of the Kernel API Manual, and honestly? It’s giving “tiny write hook, big main-character energy.” No cap, bestie — let’s get into it.

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💖 NAME

sysfs_ctlreg_write — the write method for writing to ctlreg. That’s the whole name moment: it writes, and it’s ctlreg’s write hook. Slay.

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✨ SYNOPSIS

ssize_t sysfs_ctlreg_write (struct file *filp , struct kobject *kobj ,
       const struct bin_attribute *bin_attr , char *buf , loff_t off , size_t
       count );

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🎀 ARGUMENTS

• filp — the open sysfs file. That’s the file door you came in through.
• kobj — the kernel kobject that contains the kernel class device.
• bin_attr — the kernel attributes passed to us.
• buf — contains the data to be written to the adapter IOREG space. This is the payload, bestie.
• off — offset into the buffer to the beginning of the data.
• count — bytes to transfer. Yes, we’re counting bytes. Iconic behavior.

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🦋 DESCRIPTION

You get to this through /sys/class/scsi_host/hostxxx/ctlreg. It uses the adapter io control registers to send the contents of buf over to the adapter. That’s the whole vibe — buffer contents go to the adapter through the adapter’s io control registers. Periodt.

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🌸 RETURN

• -ERANGE — the off and count combo is out of range.
• -EINVAL — off, count, or the buff address is invalid.
• -EPERM — the adapter is offline. Do not pass go, do not write ctlreg, bestie.
• The value of count — on success, and the buf contents are written. Yay, it went through! 💖

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🔥 SEE ALSO

The kernel file ./drivers/scsi/lpfc/lpfc_attr.c is in the mix, plus the whole LPFC extended universe: lpfc_jedec_to_ascii(9), lpfc_drvr_version_show(9), lpfc_enable_fip_show(9), lpfc_info_show(9), lpfc_serialnum_show(9), lpfc_temp_sensor_show(9), lpfc_modeldesc_show(9), lpfc_modelname_show(9), lpfc_programtype_show(9), lpfc_vportnum_show(9), lpfc_fwrev_show(9), lpfc_hdw_show(9), lpfc_option_rom_version_show(9), lpfc_link_state_show(9), lpfc_sli4_protocol_show(9), lpfc_oas_supported_show(9), lpfc_link_state_store(9), lpfc_num_discovered_ports_show(9), lpfc_issue_lip(9), lpfc_do_offline(9), lpfc_reset_pci_bus(9), lpfc_selective_reset(9), lpfc_issue_reset(9), lpfc_sli4_pdev_status_reg_wait(9), lpfc_sli4_pdev_reg_request(9), lpfc_nport_evt_cnt_show(9), lpfc_board_mode_show(9), lpfc_board_mode_store(9), lpfc_get_hba_info(9), lpfc_max_rpi_show(9), lpfc_used_rpi_show(9), lpfc_max_xri_show(9), lpfc_used_xri_show(9), lpfc_max_vpi_show(9), lpfc_used_vpi_show(9), lpfc_npiv_info_show(9), lpfc_poll_show(9), lpfc_poll_store(9), lpfc_sriov_hw_max_virtfn_show(9), lpfc_enable_bbcr_set(9), lpfc_wwn_set(9), lpfc_oas_tgt_show(9), lpfc_oas_tgt_store(9), lpfc_oas_priority_show(9), lpfc_oas_priority_store(9), lpfc_oas_vpt_show(9), lpfc_oas_vpt_store(9), lpfc_oas_lun_state_show(9), lpfc_oas_lun_state_store(9), lpfc_oas_lun_status_show(9), lpfc_oas_lun_state_set(9), lpfc_oas_lun_get_next(9), lpfc_oas_lun_state_change(9), lpfc_oas_lun_show(9), lpfc_oas_lun_store(9), lpfc_nodev_tmo_show(9), lpfc_nodev_tmo_init(9), lpfc_update_rport_devloss_tmo(9), lpfc_nodev_tmo_set(9), lpfc_devloss_tmo_set(9), lpfc_tgt_queue_depth_set(9), lpfc_restrict_login_init(9), lpfc_restrict_login_set(9), lpfc_topology_store(9), lpfc_static_vport_show(9), lpfc_link_speed_store(9), lpfc_link_speed_init(9), lpfc_aer_support_store(9), lpfc_aer_cleanup_state(9), lpfc_sriov_nr_virtfn_store(9), lpfc_request_firmware_upgrade_store(9), lpfc_request_firmware_upgrade_init(9), lpfc_force_rscn_store(9), lpfc_force_rscn_init(9), lpfc_fcp_imax_store(9), lpfc_fcp_imax_init(9), lpfc_cq_max_proc_limit_store(9), lpfc_cq_max_proc_limit_init(9), lpfc_fcp_cpu_map_show(9), lpfc_fcp_cpu_map_store(9), lpfc_fcp_cpu_map_init(9), lpfc_cpumask_irq_mode_init(9), lpfc_irq_chann_show(9), lpfc_sg_seg_cnt_show(9), lpfc_sg_seg_cnt_init(9), sysfs_ctlreg_read(9), sysfs_mbox_write(9), sysfs_mbox_read(9), lpfc_alloc_sysfs_attr(9), lpfc_free_sysfs_attr(9), lpfc_get_host_symbolic_name(9), lpfc_get_host_port_id(9), lpfc_get_host_port_type(9), lpfc_get_host_port_state(9), lpfc_get_host_speed(9), lpfc_get_host_fabric_name(9), lpfc_get_stats(9), lpfc_reset_stats(9), lpfc_get_enc_info(9), lpfc_get_node_by_target(9), lpfc_get_starget_port_id(9), lpfc_get_starget_node_name(9), lpfc_get_starget_port_name(9), lpfc_set_rport_loss_tmo(9), lpfc_set_vport_symbolic_name(9), lpfc_hba_log_verbose_init(9), lpfc_get_hba_function_mode(9), lpfc_get_cfgparam(9), lpfc_nvme_mod_param_dep(9), lpfc_get_vport_cfgparam(9).

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xoxo, your fave little page from ./drivers/scsi/lpfc, October 2026 — stay slay, check your off/count combo, and don’t write while the adapter’s offline 💅✨🫶