Securelevels and /dev/io documentation inconsistency

[Alexandros Kosiaris]

Hello,

I believe i have stumbled upon a documentation inconsistency
concerning securelevels and usage of /dev/io

>From init(8) manpage

  1     Secure mode - the system immutable and system append-only flags may
           not be turned off; disks for mounted file systems, /dev/mem,
           /dev/kmem and /dev/io (if your platform has it) may not be opened
           for writing; kernel modules (see kld(4)) may not be loaded or
           unloaded.

Note the "may not be opened for writing". It is correct for /dev/mem
and /dev/kmem but incorrect for /dev/io as the following experiment
shows:

3:40pm  ~ # sysctl kern.securelevel
kern.securelevel: 1
root at mybox
3:40pm  ~ # head /dev/io
head: /dev/io: Operation not permitted
root at mybox
3:40pm  ~ #

Now the source code in /usr/src/sys/i386/i386/io.c just checks if
securelevel is greater that 0 when opening the device and return
accordingly.

However from io(4)

Note that even read-only access will grant the full I/O privileges.

Which means that changing the code to check if the device is opened
O_RDONLY and then allowing access would be a mistake cancelling the
idea of blocking access to the device through usage of the
securelevel.

I am correct about the above ?
Does the documentation need a correction in that place?

Thanks,

alex