Doubt in major and minor numbers

[rpjday@crashcourse.ca (Robert P. J. Day)]

On Sun, 16 Nov 2014, me storage wrote:

> Hi All,
>
> I am reading chapter 3 in LDD3 i checked same topics in LDD2 so i
> got some confusions.According to my understanding Major number is
> used by kernel to identify the driver i.e major number tells about
> driver . Minor number is used by the driver module to know about the
> device which is using this module i.e minor number related to device
> number can i any one please tell am i correct? if wrong please
> explain me a bit more

  for the most part, that is entirely correct -- the major number
identifies the driver (either block or char), and you can see the
current list of registered drivers with:

$ cat /proc/devices
Character devices:
  1 mem
  4 /dev/vc/0
  4 tty
  4 ttyS
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
  7 vcs
 10 misc
 13 input
...
Character devices:
  1 mem
  4 /dev/vc/0
  4 tty
  4 ttyS
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
  7 vcs
 10 misc
 13 input
...

and while the minor number *usually* then identifies a particular
instance of a device being controlled by that driver, it doesn't
*have* to. in fact, the driver is free to interpret the minor number
any way it wants but, as you suggest, it typically just refers to a
specific instance of a device.

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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