Subject: Re: mounting non-BSD partitions.
To: None <current-users@NetBSD.ORG>
From: Michael C. Richardson <firstname.lastname@example.org>
Date: 06/23/1997 15:14:15
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>>>>> "Perry" == Perry E Metzger <email@example.com> writes:
Perry> John Kohl writes:
>> >>>>> "MR" == "Michael C Richardson"
>> <firstname.lastname@example.org> writes:
MR> I'd also like to suggest that 16 bits for the major number is
MR> over doing it. I can understand 8 getting a bit tight in
MR> exceptional conditions, but 12 ought to it. I suggest major
MR> numbers are 8 or 12 bits in size, and the rest is minor
>> Solaris and IRIX use a 10-bit major number with 22-bit minor
>> numbers. That seems to work just fine, so I'd suggest we use
>> this existing practice.
>> They also use a makedevice() macro instead of makedev().
>> (makedev() makes the old compatibility-sized device numbers,
>> makedevice() creates full-sized device numbers)
Perry> How does BSDI do all this?
mknod - build special file
mknod name [c | b] major minor
mknod name [c | b] major unit subunit
The mknod command creates device special files. Normally the shell
script /dev/MAKEDEV is used to create special files for commonly known
devices; it executes mknod with the appropriate arguments and can make
all the files required for the device.
To make nodes manually, the required arguments are:
name Device name, for example ``sd'' for a SCSI disk or ``pty'' for
b | c Type of device. If the device is a block type device such as a
tape or disk drive which needs both cooked and raw special files,
the type is b. All other devices are character type devices, such
as terminal and pseudo devices, and are type c.
major The major device number is an integer number which tells the ker-
nel which device driver entry point to use. To learn what major
device number to use for a particular device, check the file
/dev/MAKEDEV to see if the device is known, or check the system
dependent device configuration file:
(for example /usr/src/sys/i386/conf/ioconf.c.i386).
minor The minor device number tells the kernel which unit and/or sub-
unit the node corresponds to on the device. It may be further
subdivided into a unit and subunit. For example, there might be a
single minor value specifying a tty line, or the unit might spec-
ify a disk unit number (a single drive) with the subunit being a
partition on that drive.
A mknod command appeared in Version 6 AT&T UNIX. The separate unit and
subunit appeared in BSD/OS 2.0.
>ls -l /dev/console
crw------- 1 root tty 0,0,0 Jun 23 11:29 /dev/console
>grep makedev /usr/include/sys/types.h
#define makedev(x,y) ((dev_t)(((x) << 20) | (y))) /* create dev_t */
#define dv_makedev(x,y,z) ((dev_t)(((x)<<20) | ((y) << 10) | (z)))
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