On Thu, Nov 06, 2008 at 01:35:02PM -0200, Eduardo M KALINOWSKI wrote: > Umarzuki Mochlis escreveu: > > $ mknod block-device b 8 68 > > > > can somebody explains why do we need major and minor in creating a > > device file like above? > > Basically for the same reason one needs both the street name and the > house number to locate a house in a city. The reason is historical. Inside the kernel they are just a single number, from which the "major" and "minor" parts can be extracted. When devices had numbers statically allocated, so a disc drive would have a major number, with partitions as minor numbers (for example), they had a purpose. Today, where the device numbers are dynamically allocated and we use udev (previously devfs) to attach names to the numbers, the major and minor separation has little meaning. Currently there is a mixture of both static names (older devices, for compatibility) and dynamic: % ls -ld /dev/hda* /dev/mapper/* /dev/usb/* brw-rw---- 1 root disk 3, 0 2008-11-06 12:51 /dev/hda brw-rw---- 1 root disk 3, 1 2008-11-06 12:51 /dev/hda1 brw-rw---- 1 root disk 3, 2 2008-11-06 12:51 /dev/hda2 brw-rw---- 1 root disk 3, 3 2008-11-06 12:51 /dev/hda3 brw-rw---- 1 root disk 3, 4 2008-11-06 12:51 /dev/hda4 brw-rw---- 1 root disk 3, 5 2008-11-06 12:51 /dev/hda5 crw-rw---- 1 root root 10, 60 2008-11-06 12:51 /dev/mapper/control brw-rw---- 1 root disk 254, 4 2008-11-06 12:51 /dev/mapper/hardknott-home brw-rw---- 1 root disk 254, 0 2008-11-06 12:51 /dev/mapper/hardknott-root brw-rw---- 1 root disk 254, 5 2008-11-06 12:51 /dev/mapper/hardknott-sbuild--chroots brw-rw---- 1 root disk 254, 3 2008-11-06 12:51 /dev/mapper/hardknott-swap brw-rw---- 1 root disk 254, 1 2008-11-06 12:51 /dev/mapper/hardknott-usr brw-rw---- 1 root disk 254, 2 2008-11-06 12:51 /dev/mapper/hardknott-var crw-rw---- 1 root root 180, 0 2008-11-06 12:51 /dev/usb/hiddev0 In this case, the hard disc and its partitions are all on block-major-3. The LVM volumes are all on block-major-254, but the partitions have a (semi-)random minor device number, depending on the order they get discovered/registered in. Regards, Roger -- .''`. Roger Leigh : :' : Debian GNU/Linux http://people.debian.org/~rleigh/ `. `' Printing on GNU/Linux? http://gutenprint.sourceforge.net/ `- GPG Public Key: 0x25BFB848 Please GPG sign your mail.
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