UNIX SCSI Drivers Overview

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UNIX SCSI DriversOverview
February 2002
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Computer Essentials
Software
Hardware
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Operating System
Applications
Utilities
User Space
Kernel Space
Process Control
Device Managers
Hardware
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Device Drivers
Application
User Space
Kernel Space
Driver
Driver
Hardware
Device
Device
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Decoupling Drivers
major number
minor number
Application access driver (1), device (2)
Switch Table
Driver(1)
Driver(4)
Hardware
Device(0)
Device(2)
Device
Device(1)
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Block vs. Character Devices
Application
Application
File System
Raw I/O
Cooked I/O
Switch Table
Block Driver
Character Driver
Hardware
Blocky Devices
Letter-y Devices
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Switch Table Entry Points
Common
Block
Character
strategy
read write ioctl
open close
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Device Nodes
Stored under /dev Special Files Type block
or character (cooked or raw) Device
Number Major Number Selects Driver from Switch
Table Minor Number Driver-Specific. device
instance device partitioning (a.k.a.
slice) device options (e.g. rewind tape)
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Driver Arguments (1)
open (dev_t dev, int flag, int open_type, cred_t
cred_p) close (dev_t dev, int flag, int
open_type, cred_t cred_p)
dev major and minor number from the device
node flag read, write, exclusive, no delays,
etc. open_type block, character, layered,
etc. cred_p pointer to users credentials
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Driver Arguments (2)
strategy (struct buf bp)
bp pointer to buffer header. kernel maintains
buffer pool. file system buffers application
I/O in memory cache. buffer processing is
asynchronous. application can do something
else while waiting on I/O
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Driver Arguments (3)
read (dev_t dev, uio_t uiop, cred_t
cred_p) write (dev_t dev, uio_t uiop, cred_t
cred_p)
dev major and minor number uio_p pointer to
user I/O structure, describes I/O cred_p pointer
to users credentials
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Driver Arguments (4)
ioctl (dev_t dev, int cmd, long arg, int
mode, cred_t cred_p, int rval_p)
dev major and minor number cmd interpreted by
driver arg (usually) pointer to cmd
arguments mode direction of transfer out or
in cred_p pointer to users credentials ral_p
pointer for returning ioctl status
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Target vs. HBA Drivers
target driver (disk)
target driver (tape)
HBA driver
Driver software
Host Adapter
Hardware
SCSI BUS
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Layered Drivers
Application
Switch Table
layered open
RDAC Driver
Driver
path table
Software
Hardware
Multi-Path Device