xref: /freebsd-src/lib/libsys/rtprio.2 (revision 8269e7673cf033aba67dab8264fe719920c70f87)

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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.Dd December 8, 2021
.Dt RTPRIO 2
.Os
.Sh NAME
.Nm rtprio ,
.Nm rtprio_thread
.Nd examine or modify realtime or idle priority
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/rtprio.h
.Ft int
.Fn rtprio "int function" "pid_t pid" "struct rtprio *rtp"
.Ft int
.Fn rtprio_thread "int function" "lwpid_t lwpid" "struct rtprio *rtp"
.Sh DESCRIPTION
The
.Fn rtprio
system call
is used to lookup or change the realtime or idle priority of a process,
or the calling thread.
The
.Fn rtprio_thread
system call
is used to lookup or change the realtime or idle priority of a thread.
.Pp
The
.Fa function
argument
specifies the operation to be performed.
RTP_LOOKUP to lookup the current priority,
and RTP_SET to set the priority.
.Pp
For the
.Fn rtprio
system call,
the
.Fa pid
argument
specifies the process to operate on,
0 for the calling thread.
When
.Fa pid
is non-zero,
the system call reports the highest priority in the process,
or sets all threads' priority in the process,
depending on value of the
.Fa function
argument.
.Pp
For the
.Fn rtprio_thread
system call,
the
.Fa lwpid
specifies the thread to operate on,
0 for the calling thread.
.Pp
The
.Fa *rtp
argument
is a pointer to a struct rtprio which is used to specify the priority and priority type.
This structure has the following form:
.Bd -literal
struct rtprio {
	u_short	type;
	u_short prio;
};
.Ed
.Pp
The value of the
.Va type
field may be RTP_PRIO_REALTIME for realtime priorities,
RTP_PRIO_NORMAL for normal priorities, and RTP_PRIO_IDLE for idle priorities.
The priority specified by the
.Va prio
field ranges between 0 and
.Dv RTP_PRIO_MAX
.Pq usually 31 .
0 is the highest possible priority.
.Pp
Realtime and idle priority is inherited through
.Fn fork
and
.Fn exec .
.Pp
A realtime thread can only be preempted by a thread of equal or
higher priority, or by an interrupt; idle priority threads will run only
when no other real/normal priority thread is runnable.
Higher real/idle priority threads
preempt lower real/idle priority threads.
Threads of equal real/idle priority are run round-robin.
.Sh RETURN VALUES
.Rv -std rtprio rtprio_thread
.Sh ERRORS
The
.Fn rtprio
and
.Fn rtprio_thread
system calls
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The rtp pointer passed to
.Fn rtprio
or
.Fn rtprio_thread
was invalid.
.It Bq Er EINVAL
The specified
.Fa prio
was out of range.
.It Bq Er EPERM
The calling thread is not allowed to set the priority.
Only
root is allowed to change the realtime or idle priority of any thread.
Exceptional privileges can be granted through the
.Xr mac_priority 4
policy and the realtime and idletime user groups.
The
.Xr sysctl 8
variable
.Va security.bsd.unprivileged_idprio
is deprecated.
If set to non-zero, it lets any user change the idle priority of threads
they own.
.It Bq Er ESRCH
The specified process or thread was not found or visible.
.El
.Sh SEE ALSO
.Xr nice 1 ,
.Xr ps 1 ,
.Xr rtprio 1 ,
.Xr setpriority 2 ,
.Xr nice 3 ,
.Xr mac_priority 4 ,
.Xr renice 8 ,
.Xr p_cansee 9
.Sh AUTHORS
.An -nosplit
The original author was
.An Henrik Vestergaard Draboel Aq Mt hvd@terry.ping.dk .
This implementation in
.Fx
was substantially rewritten by
.An David Greenman .
The
.Fn rtprio_thread
system call was implemented by
.An David Xu .