freebsd-skq/sbin/devfs/devfs.8

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.Dd December 1, 2020
.Dt DEVFS 8
.Os
.Sh NAME
.Nm devfs
.Nd "DEVFS control"
.Sh SYNOPSIS
.Nm
.Op Fl m Ar mount-point
.Ar keyword
.Ar argument ...
.Sh DESCRIPTION
The
.Nm
utility provides an interface to manipulate properties of
.Xr devfs 5
mounts.
.Pp
The rules, by default as configured by
.Pa /etc/rc.conf ,
are loaded at boot via the devfs
.Xr service 8 .
The rules can be reloaded by running the command:
.Bd -literal -offset indent
service devfs restart
.Ed
.Pp
The
.Ar keyword
argument determines the context for
the rest of the arguments.
For example,
most of the commands related to the rule subsystem must be preceded by the
.Cm rule
keyword.
The following flags are common to all keywords:
.Bl -tag -width 15n
.It Fl m Ar mount-point
Operate on
.Ar mount-point ,
which is expected to be a
.Xr devfs 5
mount.
If this option is not specified,
.Nm
operates on
.Pa /dev .
.El
.Ss Rule Subsystem
The
.Xr devfs 5
rule subsystem provides a way for the administrator of a system to control
the attributes of DEVFS nodes.
.\" XXX devfs node?  entry?  what?
Each DEVFS mount-point has a
.Dq ruleset ,
or a list of rules,
associated with it.
When a device driver creates a new node,
all the rules in the ruleset associated with each mount-point are applied
(see below) before the node becomes visible to the userland.
This permits the administrator to change the properties,
including the visibility,
of certain nodes.
For example, one might want to hide all disk nodes in a
.Xr jail 2 Ns 's
.Pa /dev .
.Ss Rule Manipulation
Rule manipulation commands follow the
.Cm rule
keyword.
The following flags are common to all of the rule manipulation commands:
.Bl -tag -width 15n
.It Fl s Ar ruleset
Operate on the ruleset with the number
.Ar ruleset .
If this is not specified,
the commands operate on the ruleset currently associated with the
specified mount-point.
.El
.Pp
The following commands are recognized:
.Bl -tag -width 15n
.It Cm rule add Oo Ar rulenum Oc Ar rulespec
Add the rule described by
.Ar rulespec
(defined below)
to the ruleset.
The rule has the number
.Ar rulenum
if it is explicitly specified;
otherwise, the rule number is automatically determined by the kernel.
.It Cm rule apply Ar rulenum | rulespec
Apply rule number
.Ar rulenum
or the rule described by
.Ar rulespec
to the mount-point.
Rules that are
.Dq applied
have their conditions checked against all nodes
in the mount-point and the actions taken if they match.
.It Cm rule applyset
Apply all the rules in the ruleset to the mount-point
(see above for the definition of
.Dq apply ) .
.It Cm rule del Ar rulenum
Delete rule number
.Ar rulenum
from the ruleset.
.It Cm rule delset
Delete all rules from the ruleset.
.It Cm rule show Op Ar rulenum
Display the rule number
.Ar rulenum ,
or all the rules in the ruleset.
The output lines (one line per rule) are expected to be valid
.Ar rulespec Ns s .
.It Cm rule showsets
Report the numbers of existing rulesets.
.It Cm ruleset Ar ruleset
Set ruleset number
.Ar ruleset
as the current ruleset for the mount-point.
.El
.Ss Rule Specification
Rules have two parts: the conditions and the actions.
The conditions determine which DEVFS nodes the rule matches
and the actions determine what should be done when a rule matches a node.
For example, a rule can be written that sets the GID to
.Dq Li operator
for all devices of type tape.
If the first token of a rule specification is a single dash
.Pq Sq Fl ,
rules are read from the standard input and the rest of the specification
is ignored.
.Pp
The following conditions are recognized.
Conditions are ANDed together when matching a device;
if OR is desired, multiple rules can be written.
.Bl -tag -width 15n
.It Cm path Ar pattern
Matches any node with a path that matches
.Ar pattern ,
which is interpreted as a
.Xr glob 3 Ns -style
pattern.
.It Cm type Ar devtype
Matches any node that is of type
.Ar devtype .
Valid types are
.Cm disk , mem , tape
and
.Cm tty .
.El
.Pp
The following actions are recognized.
Although there is no explicit delimiter between conditions and actions,
they may not be intermixed.
.Bl -tag -width 15n
.It Cm group Ar gid
Set the GID of the node to
.Ar gid ,
which may be a group name
(looked up in
.Pa /etc/group )
or number.
.It Cm hide
Hide the node.
Nodes may later be revived manually with
.Xr mknod 8
or with the
.Cm unhide
action.
Hiding a directory node effectively hides all of its child nodes.
.It Cm include Ar ruleset
Apply all the rules in ruleset number
.Ar ruleset
to the node.
This does not necessarily result in any changes to the node
(e.g., if none of the rules in the included ruleset match).
Include commands in the referenced
.Ar ruleset
are not resolved.
.It Cm mode Ar filemode
Set the file mode to
.Ar filemode ,
which is interpreted as in
.Xr chmod 1 .
.It Cm user Ar uid
Set the UID to
.Ar uid ,
which may be a user name
(looked up in
.Pa /etc/passwd )
or number.
.It Cm unhide
Unhide the node.
If the node resides in a subdirectory,
all parent directory nodes must be visible to be able to access the node.
.El
.Sh IMPLEMENTATION NOTES
Rulesets are created by the kernel at the first reference
and destroyed when the last reference disappears.
E.g., a ruleset is created when a rule is added to it or when it is set
as the current ruleset for a mount-point, and
a ruleset is destroyed when the last rule in it is deleted
and no other references to it exist
(i.e., it is not included by any rules and it is not the current ruleset
for any mount-point).
.Pp
Ruleset number 0 is the default ruleset for all new mount-points.
It is always empty, cannot be modified or deleted, and does not show up
in the output of
.Cm showsets .
.Pp
Rules and rulesets are unique to the entire system,
not a particular mount-point.
I.e., a
.Cm showsets
will return the same information regardless of the mount-point specified with
.Fl m .
The mount-point is only relevant when changing what its current ruleset is
or when using one of the apply commands.
.Sh FILES
.Bl -tag -width "Pa /usr/share/examples/etc/devfs.conf" -compact
.It Pa /etc/defaults/devfs.rules
Default
.Nm
configuration file.
.It Pa /etc/devfs.rules
Local
.Nm
configuration file.
Rulesets in here override those in
.Pa /etc/defaults/devfs.rules
with the same ruleset number, otherwise the two files are effectively merged.
.It Pa /etc/devfs.conf
Boot-time
.Nm
configuration file.
.It Pa /usr/share/examples/etc/devfs.conf
Example boot-time
.Nm
configuration file.
.El
.Sh EXAMPLES
When the system boots,
the only ruleset that exists is ruleset number 0;
since the latter may not be modified, we have to create another ruleset
before adding rules.
Note that since most of the following examples do not specify
.Fl m ,
the operations are performed on
.Pa /dev
(this only matters for things that might change the properties of nodes).
.Pp
Specify that ruleset 10 should be the current ruleset for
.Pa /dev
(if it does not already exist, it is created):
.Pp
.Dl "devfs ruleset 10"
.Pp
Add a rule that causes all nodes that have a path that matches
.Dq Li speaker
(this is only
.Pa /dev/speaker )
to have the file mode 666 (read and write for all).
Note that if any such nodes already exist, their mode will not be changed
unless this rule (or ruleset) is explicitly applied (see below).
The mode
.Em will
be changed if the node is created
.Em after
the rule is added
(e.g., the
.Pa atspeaker
module is loaded after the above rule is added):
.Pp
.Dl "devfs rule add path speaker mode 666"
.Pp
Apply all the rules in the current ruleset to all the existing nodes.
E.g., if the below rule was added after
.Pa /dev/speaker
was created,
this command will cause its file mode to be changed to 666
as prescribed by the rule:
.Pp
.Dl "devfs rule applyset"
.Pp
For all devices with a path that matches
.Dq Li snp* ,
set the file mode to 660 and the GID to
.Dq Li snoopers .
This permits users in the
.Dq Li snoopers
group to use the
.Xr snp 4
devices
(quoting the argument to
.Cm path
is often necessary to disable the shell's globbing features):
.Pp
.Dl devfs rule add path "snp*" mode 660 group snoopers
.Pp
Add a rule to ruleset number 20.
Since this ruleset is not the current ruleset for any mount-points,
this rule is never applied automatically (unless ruleset 20 becomes
a current ruleset for some mount-point at a later time):
.Pp
.Dl "devfs rule -s 20 add type disk group wheel"
.Pp
Explicitly apply all rules in ruleset number 20 to the DEVFS mount on
.Pa /my/jail/dev .
It does not matter that ruleset 20 is not the current ruleset for that
mount-point; the rules are still applied:
.Pp
.Dl "devfs -m /my/jail/dev rule -s 20 applyset"
.Pp
Since the following rule has no conditions, the action
.Pq Cm hide
will be applied to all nodes:
.Pp
.Dl "devfs rule apply hide"
.Pp
Since hiding all nodes is not very useful, we can undo it.
The following applies
.Cm unhide
to all the nodes,
causing them to reappear:
.Pp
.Dl "devfs rule apply unhide"
.Pp
Add all the rules from the file
.Pa my_rules
to ruleset 10:
.Pp
.Dl "devfs rule -s 10 add - < my_rules"
.Pp
The below copies all the rules from ruleset 20 into ruleset 10.
The rule numbers are preserved,
but ruleset 10 may already have rules with non-conflicting numbers
(these will be preserved).
Since
.Cm show
outputs valid rules,
this feature can be used to copy rulesets:
.Pp
.Dl "devfs rule -s 20 show | devfs rule -s 10 add -"
.Sh SEE ALSO
.Xr chmod 1 ,
.Xr jail 2 ,
.Xr glob 3 ,
.Xr devfs 5 ,
.Xr devfs.conf 5 ,
.Xr devfs.rules 5 ,
.Xr chown 8 ,
.Xr jail 8 ,
.Xr mknod 8 ,
.Xr service 8
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 5.0 .
.Sh AUTHORS
.An Dima Dorfman