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When building a target filesystem, it is desirable to not have to
become root and then run 'mknod' a thousand times. Using a device
table you can create device nodes and directories "on the fly".
You can do all sorts of interesting things with a device table file.
For example, if you want to adjust the permissions on a particular
file you can just add an entry like:
/sbin/foobar f 2755 0 0 - - - - -
and (assuming the file /sbin/foobar exists) it will be made setuid
root (regardless of what its permissions are on the host filesystem.
Furthermore, you can use a single table entry to create a many device
minors. For example, if I wanted to create /dev/hda and
/dev/hda[0-15] I could just use the following two table entries:
/dev/hda b 640 0 0 3 0 0 0 -
/dev/hda b 640 0 0 3 1 1 1 15
Device table entries take the form of:
<name> <type> <mode> <uid> <gid> <major> <minor> <start> <inc> <count>
where name is the file name, type can be one of:
f A regular file
d Directory
c Character special device file
b Block special device file
p Fifo (named pipe)
uid is the user id for the target file, gid is the group id for the
target file. The rest of the entries (major, minor, etc) apply only
to device special files.