.\" Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
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.\" $FreeBSD$
.\"
.Dd February 10, 2018
.Dt SYSCALL_HELPER_REGISTER 9
.Os
.Sh NAME
.Nm syscall_helper_register ,
.Nm syscall_helper_unregister
.Nd kernel syscall registration routines
.\"
.Sh SYNOPSIS
.In sys/sysent.h
.Ft int
.Fn syscall_helper_register "struct syscall_helper_data *sd" "int flags"
.Ft int
.Fn syscall_helper_unregister "struct syscall_helper_data *sd"
.\"
.Ss INITIALIZER MACROS
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER "syscallname"
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER_F "syscallname" "int flags"
.\"
.Ss COMPATIBILITY INITIALIZER MACROS
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER_COMPAT "syscallname"
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER_COMPAT_F "syscallname" "int flags"
.\"
.Sh DESCRIPTION
The
.Fn syscall_helper_register
registers a system call.
This function takes the structure
.Va struct syscall_helper_data sd ,
which specifies the parameters for syscall registration:
.Pp
.Bd -literal -offset indent -compact
struct syscall_helper_data {
	struct sysent	new_sysent;
	struct sysent	old_sysent;
	int		syscall_no;
	int		registered;
};
.Ed
.Pp
The only valid flag for the
.Fa flags
argument to
.Fn syscall_helper_register
is
.Dv SY_THR_STATIC .
This flag prevents the syscall from being unregistered.
.\"
.Pp
Before use, the structure must be initialized with one of the
.Fn SYSCALL_INIT_HELPER*
macros.
In new code, syscall implementation functions shall be named
.Fn sys_syscallname
and the regular macros shall be used.
.Pp
For legacy syscall functions named without "sys_" prefixes, the "COMPAT"
versions of the macros may be used.
.Pp
The only valid flag for the
.Fa flags
argument to the "F" variants of the initializer macros is
.Dv SYF_CAPENABLED .
This flag indicates that the syscall is allowed in capability mode.
.Pp
The
.Fn syscall_helper_unregister
unregisters a system call.
This function takes the same structure
.Va struct syscall_helper_data sd
that was previously initialized in the manner described above and used in a
successful invocation of
.Fn syscall_helper_register .
.\"
.Sh RETURN VALUES
If successful,
.Fn syscall_helper_register
and
.Fn syscall_helper_unregister
will return 0.
Otherwise, they will return an error.
.\"
.Sh ERRORS
The
.Fn syscall_helper_register
call will fail and the syscall will not be registered if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa flags
argument contained a value other than
.Dv SY_THR_STATIC .
.It Bq Er EINVAL
The specified syscall number,
.Dv sd.syscall_no
.Dv ( SYS_syscallname ) ,
was outside of the valid range of system call numbers (zero through
.Dv SYS_MAXSYSCALL ) .
.It Bq Er ENFILE
The system call table does not have any available slots.
.It Bq Er EEXIST
The specified syscall number,
.Dv sd.syscall_no
.Dv ( SYS_syscallname ) ,
was already in use.
.El
.\"
.Sh SEE ALSO
.Xr SYSCALL_MODULE 9