linux/Documentation/scsi/megaraid.txt
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   1                        Notes on Management Module
   2                        ~~~~~~~~~~~~~~~~~~~~~~~~~~
   3
   4Overview:
   5--------
   6
   7Different classes of controllers from LSI Logic accept and respond to the
   8user applications in a similar way. They understand the same firmware control
   9commands. Furthermore, the applications also can treat different classes of
  10the controllers uniformly. Hence it is logical to have a single module that
  11interfaces with the applications on one side and all the low level drivers
  12on the other.
  13
  14The advantages, though obvious, are listed for completeness:
  15
  16        i.      Avoid duplicate code from the low level drivers.
  17        ii.     Unburden the low level drivers from having to export the
  18                character node device and related handling.
  19        iii.    Implement any policy mechanisms in one place.
  20        iv.     Applications have to interface with only module instead of
  21                multiple low level drivers.
  22
  23Currently this module (called Common Management Module) is used only to issue
  24ioctl commands. But this module is envisioned to handle all user space level
  25interactions. So any 'proc', 'sysfs' implementations will be localized in this
  26common module.
  27
  28Credits:
  29-------
  30
  31"Shared code in a third module, a "library module", is an acceptable
  32solution. modprobe automatically loads dependent modules, so users
  33running "modprobe driver1" or "modprobe driver2" would automatically
  34load the shared library module."
  35
  36                - Jeff Garzik (jgarzik@pobox.com), 02.25.2004 LKML
  37
  38"As Jeff hinted, if your userspace<->driver API is consistent between
  39your new MPT-based RAID controllers and your existing megaraid driver,
  40then perhaps you need a single small helper module (lsiioctl or some
  41better name), loaded by both mptraid and megaraid automatically, which
  42handles registering the /dev/megaraid node dynamically. In this case,
  43both mptraid and megaraid would register with lsiioctl for each
  44adapter discovered, and lsiioctl would essentially be a switch,
  45redirecting userspace tool ioctls to the appropriate driver."
  46
  47                - Matt Domsch, (Matt_Domsch@dell.com), 02.25.2004 LKML
  48
  49Design:
  50------
  51
  52The Common Management Module is implemented in megaraid_mm.[ch] files. This
  53module acts as a registry for low level hba drivers. The low level drivers
  54(currently only megaraid) register each controller with the common module.
  55
  56The applications interface with the common module via the character device
  57node exported by the module.
  58
  59The lower level drivers now understand only a new improved ioctl packet called
  60uioc_t. The management module converts the older ioctl packets from the older
  61applications into uioc_t. After driver handles the uioc_t, the common module
  62will convert that back into the old format before returning to applications.
  63
  64As new applications evolve and replace the old ones, the old packet format 
  65will be retired.
  66
  67Common module dedicates one uioc_t packet to each controller registered. This
  68can easily be more than one. But since megaraid is the only low level driver
  69today, and it can handle only one ioctl, there is no reason to have more. But
  70as new controller classes get added, this will be tuned appropriately.
  71
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