[hb][jails] Fix jail configuration example

[fernape]

Summary

jail.conf(8) accepts a devfs_ruleset that should be specified as a number
according to jail(8):

devfs_ruleset
The number of the devfs ruleset that is enforced for mounting
devfs in this jail. A value of zero (default) means no ruleset.

With the example in the handbook, we get this error when trying to launch the
jail:

Starting jails: cannot start jail  "www":
jail: www: devfs_ruleset: non-integer value "www_ruleset"

Remove that from the handbook and left the default value of 0, meaning no
ruleset is enforced. No need to go into explaining devfs(8) at this point.

Test Plan

Create an entry in /etc/jail.conf with the contents from the handbook:

www {
    host.hostname = www.example.org;           # Hostname
    ip4.addr = 192.168.0.10;                   # IP address of the jail
    path = "/usr/jail/www";                    # Path to the jail
    devfs_ruleset = "www_ruleset";             # devfs ruleset
    mount.devfs;                               # Mount devfs inside the jail
    exec.start = "/bin/sh /etc/rc";            # Start command
    exec.stop = "/bin/sh /etc/rc.shutdown";    # Stop command
}

No need to create the real jail, just try to start it:

$ sudo service jail onestart www
Starting jails: cannot start jail  "www":
jail: www: devfs_ruleset: non-integer value "www_ruleset"

[zlei]

Remove that from the handbook and left the default value of 0, meaning no
ruleset is enforced

This seems to be inconsistent with mount.devfs, which says the default devfs_ruleset is 4 ( devfsrules_jail ).

[0mp]

Great catch!

[0mp]

In D35630#808272, @zlei.huang_gmail.com wrote:

Remove that from the handbook and left the default value of 0, meaning no
ruleset is enforced

This seems to be inconsistent with mount.devfs, which says the default devfs_ruleset is 4 ( devfsrules_jail ).

Hmm, that’s true. The manual page is a bit confusing.

[fernape]

In D35630#808274, @0mp wrote:

In D35630#808272, @zlei.huang_gmail.com wrote:

Remove that from the handbook and left the default value of 0, meaning no
ruleset is enforced

This seems to be inconsistent with mount.devfs, which says the default devfs_ruleset is 4 ( devfsrules_jail ).

Hmm, that’s true. The manual page is a bit confusing.

The code confirms what Zlei Huang pointed out.
I can go with the update of the Handbook and try to clarify jail(8) in another review.

[fernape]

Landed. Thanks for the review!

So IIUC, devfs_ruleset is 0 if not defined. Then, mount.devfs takes the value of devfs_ruleset if defined and != 0. If undefined or 0, then it takes value 4 (devfsrules_jail)