Creating filesystem images with device tables

The kernel has a utility, gen_init_cpio, that creates a cpio file based on format instructions set out in a text file, called a device table, which allows a non-root user to create device nodes and to allocate arbitrary UID and GID values to any file or directory.

The same concept has been applied to tools that create other filesystem image formats:

• jffs2: mkfs.jffs2

• ubifs: mkfs.ubifs

• ext2: genext2fs

We will look at jffs2 and ubifs in Chapter 7, Creating a Storage Strategy, when we look at filesystems for flash memory. The third, ext2, is a fairly old format for hard drives.

They each take a device table file with the format <name> <type> <mode> <uid> <gid> <major> <minor> <start> <inc> <count> in which the following applies:

• name: Filename

• type: One of the following:

  • f: A regular file

  • d: A directory

  • c: A character special device file

  • b: A block special device file

  • p: A FIFO (named pipe)

• uid The...