[apple/xnu.git] / bsd / man / man2 / semget.2

.\"
.\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
.\"
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD: src/lib/libc/sys/semget.2,v 1.14 2002/12/19 09:40:25 ru Exp $
.\"
.Dd September 12, 1995
.Dt SEMGET 2
.Os
.Sh NAME
.Nm semget
.Nd obtain a semaphore id
.Sh SYNOPSIS
.In sys/types.h
.In sys/ipc.h
.In sys/sem.h
.Ft int
.Fn semget "key_t key" "int nsems" "int flag"
.Sh DESCRIPTION
Based on the values of
.Fa key
and
.Fa flag ,
.Fn semget
returns the identifier of a newly created or previously existing
set of semaphores.
.\"
.\" This is copied verbatim from the shmget manpage.  Perhaps
.\" it should go in a common manpage, such as .Xr ipc 2
.\"
The key
is analogous to a filename: it provides a handle that names an
IPC object.  There are three ways to specify a key:
.Bl -bullet
.It
IPC_PRIVATE may be specified, in which case a new IPC object
will be created.
.It
An integer constant may be specified.  If no IPC object corresponding
to
.Fa key
is specified and the IPC_CREAT bit is set in
.Fa flag ,
a new one will be created.
.It
The
.Xr ftok 3
function
may be used to generate a key from a pathname.
.El
.\"
.\" Likewise for this section, except SHM_* becomes SEM_*.
.\"
.Pp
The mode of a newly created IPC object is determined by
.Em OR Ns 'ing
the following constants into the
.Fa flag
argument:
.Bl -tag -width XSEM_WXX6XXX
.It Dv SEM_R
Read access for user.
.It Dv SEM_A
Alter access for user.
.It Dv ( SEM_R>>3 )
Read access for group.
.It Dv ( SEM_A>>3 )
Alter access for group.
.It Dv ( SEM_R>>6 )
Read access for other.
.It Dv ( SEM_A>>6 )
Alter access for other.
.El
.Pp
If a new set of semaphores is being created,
.Fa nsems
is used to indicate the number of semaphores the set should contain.
Otherwise,
.Fa nsems
may be specified as 0.
.Sh RETURN VALUES
The
.Fn semget
system call
returns the id of a semaphore set if successful; otherwise, -1
is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn semget
system call
will fail if:
.Bl -tag -width Er
.\" ipcperm could fail (we're opening to read and write, as it were)
.It Bq Er EACCES
Access permission failure.
.\"
.\" sysv_sem.c is quite explicit about these, so I'm pretty sure
.\" this is accurate
.\"
.It Bq Er EEXIST
IPC_CREAT and IPC_EXCL were specified, and a semaphore set
corresponding to
.Fa key
already exists.
.It Bq Er EINVAL
The number of semaphores requested exceeds the system imposed maximum
per set.
.It Bq Er ENOSPC
Insufficiently many semaphores are available.
.It Bq Er ENOSPC
The kernel could not allocate a
.Fa "struct semid_ds" .
.It Bq Er ENOENT
No semaphore set was found corresponding to
.Fa key ,
and IPC_CREAT was not specified.
.El
.Sh SEE ALSO
.Xr semctl 2 ,
.Xr semop 2 ,
.Xr ftok 3
Commit	Line	Data
55e303ae A	1	.\"
	2	.\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
	3	.\"
	4	.\" All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\"
	15	.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
	16	.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	17	.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	18	.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
	19	.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	20	.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	21	.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	22	.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	23	.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	24	.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	25	.\"
	26	.\" $FreeBSD: src/lib/libc/sys/semget.2,v 1.14 2002/12/19 09:40:25 ru Exp $
	27	.\"
	28	.Dd September 12, 1995
	29	.Dt SEMGET 2
	30	.Os
	31	.Sh NAME
	32	.Nm semget
	33	.Nd obtain a semaphore id
55e303ae A	34	.Sh SYNOPSIS
	35	.In sys/types.h
	36	.In sys/ipc.h
	37	.In sys/sem.h
	38	.Ft int
	39	.Fn semget "key_t key" "int nsems" "int flag"
	40	.Sh DESCRIPTION
	41	Based on the values of
	42	.Fa key
	43	and
	44	.Fa flag ,
	45	.Fn semget
	46	returns the identifier of a newly created or previously existing
	47	set of semaphores.
	48	.\"
	49	.\" This is copied verbatim from the shmget manpage. Perhaps
	50	.\" it should go in a common manpage, such as .Xr ipc 2
	51	.\"
	52	The key
	53	is analogous to a filename: it provides a handle that names an
	54	IPC object. There are three ways to specify a key:
	55	.Bl -bullet
	56	.It
	57	IPC_PRIVATE may be specified, in which case a new IPC object
	58	will be created.
	59	.It
	60	An integer constant may be specified. If no IPC object corresponding
	61	to
	62	.Fa key
	63	is specified and the IPC_CREAT bit is set in
	64	.Fa flag ,
	65	a new one will be created.
	66	.It
	67	The
	68	.Xr ftok 3
	69	function
	70	may be used to generate a key from a pathname.
	71	.El
	72	.\"
	73	.\" Likewise for this section, except SHM_* becomes SEM_*.
	74	.\"
	75	.Pp
	76	The mode of a newly created IPC object is determined by
	77	.Em OR Ns 'ing
	78	the following constants into the
	79	.Fa flag
	80	argument:
	81	.Bl -tag -width XSEM_WXX6XXX
	82	.It Dv SEM_R
	83	Read access for user.
	84	.It Dv SEM_A
	85	Alter access for user.
	86	.It Dv ( SEM_R>>3 )
	87	Read access for group.
	88	.It Dv ( SEM_A>>3 )
	89	Alter access for group.
	90	.It Dv ( SEM_R>>6 )
	91	Read access for other.
	92	.It Dv ( SEM_A>>6 )
	93	Alter access for other.
	94	.El
	95	.Pp
	96	If a new set of semaphores is being created,
	97	.Fa nsems
98	is used to indicate the number of semaphores the set should contain.
99	Otherwise,
100	.Fa nsems
101	may be specified as 0.
102	.Sh RETURN VALUES
103	The
104	.Fn semget
105	system call
106	returns the id of a semaphore set if successful; otherwise, -1
107	is returned and
108	.Va errno
109	is set to indicate the error.
110	.Sh ERRORS
111	The
112	.Fn semget
113	system call
114	will fail if:
115	.Bl -tag -width Er
116	.\" ipcperm could fail (we're opening to read and write, as it were)
117	.It Bq Er EACCES
118	Access permission failure.
119	.\"
120	.\" sysv_sem.c is quite explicit about these, so I'm pretty sure
121	.\" this is accurate
122	.\"
123	.It Bq Er EEXIST
124	IPC_CREAT and IPC_EXCL were specified, and a semaphore set
125	corresponding to
126	.Fa key
127	already exists.
128	.It Bq Er EINVAL
129	The number of semaphores requested exceeds the system imposed maximum
130	per set.
131	.It Bq Er ENOSPC
132	Insufficiently many semaphores are available.
133	.It Bq Er ENOSPC
134	The kernel could not allocate a
135	.Fa "struct semid_ds" .
136	.It Bq Er ENOENT
137	No semaphore set was found corresponding to
138	.Fa key ,
139	and IPC_CREAT was not specified.
140	.El
141	.Sh SEE ALSO
142	.Xr semctl 2 ,
143	.Xr semop 2 ,
144	.Xr ftok 3