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.Dd March 12, 1998
.Dt SCHED_SETSCHEDULER 2
.Os
.Sh NAME
.Nm sched_setscheduler ,
.Nm sched_getscheduler
.Nd set/get scheduling policy and scheduler parameters
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sched.h
.Ft int
.Fn sched_setscheduler "pid_t pid" "int policy" "const struct sched_param *param"
.Ft int
.Fn sched_getscheduler "pid_t pid"
.Sh DESCRIPTION
The
.Fn sched_setscheduler
system call sets the scheduling policy and scheduling parameters
of the process specified by
.Fa pid
to
.Fa policy
and the parameters specified in the
.Vt sched_param
structure pointed to by
.Fa param ,
respectively.
The value of the
.Fa sched_priority
member in the
.Fa param
structure must be any integer within the inclusive priority range for
the scheduling policy specified by
.Fa policy .
.Pp
In this implementation, if the value of
.Fa pid
is negative the system call will fail.
.Pp
If a process specified by
.Fa pid
exists and if the calling process has permission, the scheduling
policy and scheduling parameters will be set for the process
whose process ID is equal to
.Fa pid .
.Pp
If
.Fa pid
is zero, the scheduling policy and scheduling
parameters are set for the calling process.
.Pp
In this implementation, the policy of when a process can affect
the scheduling parameters of another process is specified in
.St -p1003.1b-93
as a write-style operation.
.Pp
The scheduling policies are in
.Fa <sched.h> :
.Bl -tag -width [SCHED_OTHER]
.It Bq Er SCHED_FIFO
First-in-first-out fixed priority scheduling with no round robin scheduling;
.It Bq Er SCHED_OTHER
The standard time sharing scheduler;
.It Bq Er SCHED_RR
Round-robin scheduling across same priority processes.
.El
.Pp
The
.Vt sched_param
structure is defined in
.Fa <sched.h> :
.Pp
.Bd -literal -offset indent
struct sched_param {
	int sched_priority;	/* scheduling priority */
};
.Ed
.Pp
The
.Fn sched_getscheduler
system call returns the scheduling policy of the process specified
by
.Fa pid .
.Pp
If a process specified by
.Fa pid
exists and if the calling process has permission,
the scheduling parameters for the process whose process ID is equal to
.Fa pid
are returned.
.Pp
In this implementation, the policy of when a process can obtain the
scheduling parameters of another process are detailed in
.St -p1003.1b-93
as a read-style operation.
.Pp
If
.Fa pid
is zero, the scheduling parameters for the calling process will be
returned.
In this implementation, the
.Fa sched_getscheduler
system call will fail if
.Fa pid
is negative.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
On failure
.Va errno
will be set to the corresponding value:
.Bl -tag -width Er
.It Bq Er ENOSYS
The system is not configured to support this functionality.
.It Bq Er EPERM
The requesting process doesn not have permission as detailed in
.St -p1003.1b-93 .
.It Bq Er ESRCH
No process can be found corresponding to that specified by
.Fa pid .
.It Bq Er EINVAL
The value of the
.Fa policy
argument is invalid, or one or more of the parameters contained in
.Fa param
is outside the valid range for the specified scheduling policy.
.El
.Sh SEE ALSO
.Xr sched_getparam 2 ,
.Xr sched_get_priority_max 2 ,
.Xr sched_get_priority_min 2 ,
.Xr sched_rr_get_interval 2 ,
.Xr sched_setparam 2 ,
.Xr sched_yield 2
.Sh STANDARDS
The
.Fn sched_setscheduler
and
.Fn sched_getscheduler
system calls conform to
.St -p1003.1b-93 .