78 lines
3.1 KiB
ReStructuredText
78 lines
3.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=================================
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Megaraid Common Management Module
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=================================
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Overview
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--------
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Different classes of controllers from LSI Logic accept and respond to the
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user applications in a similar way. They understand the same firmware control
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commands. Furthermore, the applications also can treat different classes of
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the controllers uniformly. Hence it is logical to have a single module that
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interfaces with the applications on one side and all the low level drivers
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on the other.
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The advantages, though obvious, are listed for completeness:
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i. Avoid duplicate code from the low level drivers.
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ii. Unburden the low level drivers from having to export the
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character node device and related handling.
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iii. Implement any policy mechanisms in one place.
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iv. Applications have to interface with only module instead of
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multiple low level drivers.
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Currently this module (called Common Management Module) is used only to issue
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ioctl commands. But this module is envisioned to handle all user space level
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interactions. So any 'proc', 'sysfs' implementations will be localized in this
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common module.
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Credits
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-------
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::
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"Shared code in a third module, a "library module", is an acceptable
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solution. modprobe automatically loads dependent modules, so users
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running "modprobe driver1" or "modprobe driver2" would automatically
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load the shared library module."
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- Jeff Garzik (jgarzik@pobox.com), 02.25.2004 LKML
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::
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"As Jeff hinted, if your userspace<->driver API is consistent between
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your new MPT-based RAID controllers and your existing megaraid driver,
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then perhaps you need a single small helper module (lsiioctl or some
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better name), loaded by both mptraid and megaraid automatically, which
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handles registering the /dev/megaraid node dynamically. In this case,
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both mptraid and megaraid would register with lsiioctl for each
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adapter discovered, and lsiioctl would essentially be a switch,
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redirecting userspace tool ioctls to the appropriate driver."
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- Matt Domsch, (Matt_Domsch@dell.com), 02.25.2004 LKML
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Design
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------
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The Common Management Module is implemented in megaraid_mm.[ch] files. This
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module acts as a registry for low level hba drivers. The low level drivers
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(currently only megaraid) register each controller with the common module.
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The applications interface with the common module via the character device
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node exported by the module.
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The lower level drivers now understand only a new improved ioctl packet called
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uioc_t. The management module converts the older ioctl packets from the older
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applications into uioc_t. After driver handles the uioc_t, the common module
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will convert that back into the old format before returning to applications.
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As new applications evolve and replace the old ones, the old packet format
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will be retired.
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Common module dedicates one uioc_t packet to each controller registered. This
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can easily be more than one. But since megaraid is the only low level driver
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today, and it can handle only one ioctl, there is no reason to have more. But
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as new controller classes get added, this will be tuned appropriately.
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