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When a LUN is replaced, scst_acg_repl_lun polls tgt_dev_cmd_count every 100ms waiting for in-flight commands on the old tgt_devs to drain before freeing them. This is synchronous: the sysfs write to luns/mgmt blocks until the drain completes. If the old device becomes unreachable before the LUN replace (e.g. due to a transport failure), in-flight commands may be stuck in error recovery for up to the transport's recovery timeout, blocking the replace for that entire window. Add a bool module parameter async_lun_replace (default false). When enabled, scst_acg_repl_lun schedules the tgt_dev drain and free on system_wq and returns immediately. Falls back to synchronous behaviour on allocation failure. This is safe because __scst_acg_del_lun removes the old tgt_devs from all session and device lookup paths before the work is scheduled. New commands from the initiator use the new tgt_devs; only in-flight commands still hold references via cmd->tgt_dev, and tgt_dev_cmd_count tracks exactly those. synchronize_rcu ensures no RCU reader holds a stale pointer before scst_free_tgt_dev is called.
Overview
This is the source code repository of the SCST project. SCST is a collection of Linux kernel drivers that implement SCSI target functionality. The SCST project includes:
- The SCST core in the scst/ subdirectory.
- A tool for loading, saving and modifying the SCST configuration in directory scstadmin/.
- Several SCSI target drivers in the directories iscsi-scst/, qla2x00t/, srpt/, scst_local/ and fcst/.
- User space programs in the usr/ subdirectory, e.g. fileio_tgt.
- Various documentation in the doc/ subdirectory.
Instructions for building and installing SCST are available in the INSTALL.md file.
QLogic target driver
Two QLogic target drivers are included in the SCST project.
The default driver is located in qla2x00t-32gbit directory and it supports up to 32 Gb/s FC. It is the newer one.
May anyone wish to switch back to the older driver that only supported up to
16 Gb/s adapters, it is located in qla2x00t directory. To make use of the
older driver build scst with environment variable QLA_32GBIT=no set.
Vladislav Bolkhovitin vst@vlnb.net, http://scst.sourceforge.net
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