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This procedure, which implements a system call of the same name, is only executable by the super-user. As explained in the Section “MKNOD(II)” of the UPM, this system call is used to create “inodes” for special files.
“mknod” also solves the problem of “where do directories come from”? The second parameter passed to “mknod” is used, without modification or restriction to set “i_mode”. (Compare “creat” (5790) and “chmod” (3569)). This is the only way an “inode” can get flagged as a directory, for instance.
In such cases, the third parameter passed to “mknod” must be zero. This value is copied into “i_addr[0]” (as is appropriate for special files), and, if non-zero, will be accepted uncritically by “bmap” (6447). It might be prudent to insert a test
if (ip->i_mode & (IFCHR & IFBLK) != 0)
before line 5969, rather than rely indefinitely on the infallibility of the super-user.
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