543 lines
15 KiB
Groff
543 lines
15 KiB
Groff
.\" Copyright (c) 1992, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Casey Leedom of Lawrence Livermore National Laboratory.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getcap.3 8.4 (Berkeley) 5/13/94
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.\" $FreeBSD$
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.\"
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.Dd May 13, 1994
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.Dt GETCAP 3
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.Os
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.Sh NAME
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.Nm cgetent ,
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.Nm cgetset ,
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.Nm cgetmatch ,
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.Nm cgetcap ,
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.Nm cgetnum ,
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.Nm cgetstr ,
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.Nm cgetustr ,
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.Nm cgetfirst ,
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.Nm cgetnext ,
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.Nm cgetclose
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.Nd capability database access routines
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <stdlib.h>
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.Ft int
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.Fn cgetent "char **buf" "char **db_array" "char *name"
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.Ft int
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.Fn cgetset "char *ent"
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.Ft int
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.Fn cgetmatch "char *buf" "char *name"
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.Ft char *
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.Fn cgetcap "char *buf" "char *cap" "int type"
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.Ft int
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.Fn cgetnum "char *buf" "char *cap" "long *num"
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.Ft int
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.Fn cgetstr "char *buf" "char *cap" "char **str"
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.Ft int
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.Fn cgetustr "char *buf" "char *cap" "char **str"
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.Ft int
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.Fn cgetfirst "char **buf" "char **db_array"
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.Ft int
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.Fn cgetnext "char **buf" "char **db_array"
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.Ft int
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.Fn cgetclose "void"
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.Sh DESCRIPTION
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The
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.Fn cgetent
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function extracts the capability
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.Fa name
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from the database specified by the
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.Dv NULL
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terminated file array
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.Fa db_array
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and returns a pointer to a
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.Xr malloc 3 Ns \&'d
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copy of it in
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.Fa buf .
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The
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.Fn cgetent
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function will first look for files ending in
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.Pa .db
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(see
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.Xr cap_mkdb 1 )
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before accessing the ASCII file.
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.Fa Buf
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must be retained through all subsequent calls to
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.Fn cgetmatch ,
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.Fn cgetcap ,
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.Fn cgetnum ,
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.Fn cgetstr ,
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and
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.Fn cgetustr ,
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but may then be
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.Xr free 3 Ns \&'d .
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On success 0 is returned, 1 if the returned
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record contains an unresolved
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.Nm tc
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expansion,
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\-1 if the requested record couldn't be found,
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\-2 if a system error was encountered (couldn't open/read a file, etc.) also
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setting
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.Va errno ,
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and \-3 if a potential reference loop is detected (see
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.Ic tc=
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comments below).
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.Pp
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The
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.Fn cgetset
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function enables the addition of a character buffer containing a single capability
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record entry
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to the capability database.
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Conceptually, the entry is added as the first ``file'' in the database, and
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is therefore searched first on the call to
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.Fn cgetent .
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The entry is passed in
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.Fa ent .
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If
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.Fa ent
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is
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.Dv NULL ,
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the current entry is removed from the database.
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A call to
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.Fn cgetset
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must precede the database traversal. It must be called before the
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.Fn cgetent
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call. If a sequential access is being performed (see below), it must be called
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before the first sequential access call
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.Fn ( cgetfirst
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or
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.Fn cgetnext ) ,
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or be directly preceded by a
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.Fn cgetclose
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call.
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On success 0 is returned and \-1 on failure.
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.Pp
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The
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.Fn cgetmatch
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function will return 0 if
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.Fa name
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is one of the names of the capability record
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.Fa buf ,
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\-1 if
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not.
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.Pp
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The
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.Fn cgetcap
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function searches the capability record
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.Fa buf
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for the capability
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.Fa cap
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with type
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.Fa type .
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A
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.Fa type
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is specified using any single character. If a colon (`:') is used, an
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untyped capability will be searched for (see below for explanation of
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types). A pointer to the value of
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.Fa cap
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in
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.Fa buf
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is returned on success,
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.Dv NULL
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if the requested capability couldn't be
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found. The end of the capability value is signaled by a `:' or
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.Tn ASCII
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.Dv NUL
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(see below for capability database syntax).
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.Pp
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The
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.Fn cgetnum
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function retrieves the value of the numeric capability
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.Fa cap
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from the capability record pointed to by
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.Fa buf .
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The numeric value is returned in the
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.Ft long
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pointed to by
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.Fa num .
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0 is returned on success, \-1 if the requested numeric capability couldn't
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be found.
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.Pp
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The
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.Fn cgetstr
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function retrieves the value of the string capability
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.Fa cap
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from the capability record pointed to by
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.Fa buf .
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A pointer to a decoded,
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.Dv NUL
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terminated,
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.Xr malloc 3 Ns \&'d
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copy of the string is returned in the
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.Ft char *
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pointed to by
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.Fa str .
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The number of characters in the decoded string not including the trailing
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.Dv NUL
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is returned on success, \-1 if the requested string capability couldn't
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be found, \-2 if a system error was encountered (storage allocation
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failure).
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.Pp
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The
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.Fn cgetustr
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function is identical to
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.Fn cgetstr
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except that it does not expand special characters, but rather returns each
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character of the capability string literally.
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.Pp
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The
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.Fn cgetfirst
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and
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.Fn cgetnext
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functions comprise a function group that provides for sequential
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access of the
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.Dv NULL
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pointer terminated array of file names,
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.Fa db_array .
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The
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.Fn cgetfirst
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function returns the first record in the database and resets the access
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to the first record.
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The
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.Fn cgetnext
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function returns the next record in the database with respect to the
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record returned by the previous
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.Fn cgetfirst
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or
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.Fn cgetnext
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call. If there is no such previous call, the first record in the database is
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returned.
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Each record is returned in a
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.Xr malloc 3 Ns \&'d
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copy pointed to by
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.Fa buf .
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.Ic Tc
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expansion is done (see
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.Ic tc=
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comments below).
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Upon completion of the database 0 is returned, 1 is returned upon successful
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return of record with possibly more remaining (we haven't reached the end of
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the database yet), 2 is returned if the record contains an unresolved
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.Nm tc
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expansion, \-1 is returned if an system error occurred, and \-2
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is returned if a potential reference loop is detected (see
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.Ic tc=
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comments below).
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Upon completion of database (0 return) the database is closed.
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.Pp
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The
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.Fn cgetclose
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function closes the sequential access and frees any memory and file descriptors
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being used. Note that it does not erase the buffer pushed by a call to
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.Fn cgetset .
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.Sh CAPABILITY DATABASE SYNTAX
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Capability databases are normally
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.Tn ASCII
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and may be edited with standard
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text editors. Blank lines and lines beginning with a `#' are comments
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and are ignored. Lines ending with a `\|\e' indicate that the next line
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is a continuation of the current line; the `\|\e' and following newline
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are ignored. Long lines are usually continued onto several physical
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lines by ending each line except the last with a `\|\e'.
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.Pp
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Capability databases consist of a series of records, one per logical
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line. Each record contains a variable number of `:'-separated fields
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(capabilities). Empty fields consisting entirely of white space
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characters (spaces and tabs) are ignored.
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.Pp
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The first capability of each record specifies its names, separated by `|'
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characters. These names are used to reference records in the database.
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By convention, the last name is usually a comment and is not intended as
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a lookup tag. For example, the
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.Em vt100
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record from the
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.Nm termcap
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database begins:
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.Pp
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.Dl "d0\||\|vt100\||\|vt100-am\||\|vt100am\||\|dec vt100:"
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.Pp
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giving four names that can be used to access the record.
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.Pp
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The remaining non-empty capabilities describe a set of (name, value)
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bindings, consisting of a names optionally followed by a typed value:
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.Bl -column "nameTvalue"
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.It name Ta "typeless [boolean] capability"
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.Em name No "is present [true]"
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.It name Ns Em \&T Ns value Ta capability
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.Pq Em name , \&T
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has value
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.Em value
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.It name@ Ta "no capability" Em name No exists
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.It name Ns Em T Ns \&@ Ta capability
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.Pq Em name , T
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does not exist
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.El
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.Pp
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Names consist of one or more characters. Names may contain any character
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except `:', but it's usually best to restrict them to the printable
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characters and avoid use of graphics like `#', `=', `%', `@', etc. Types
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are single characters used to separate capability names from their
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associated typed values. Types may be any character except a `:'.
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Typically, graphics like `#', `=', `%', etc. are used. Values may be any
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number of characters and may contain any character except `:'.
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.Sh CAPABILITY DATABASE SEMANTICS
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Capability records describe a set of (name, value) bindings. Names may
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have multiple values bound to them. Different values for a name are
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distinguished by their
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.Fa types .
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The
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.Fn cgetcap
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function will return a pointer to a value of a name given the capability
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name and the type of the value.
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.Pp
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The types `#' and `=' are conventionally used to denote numeric and
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string typed values, but no restriction on those types is enforced. The
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functions
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.Fn cgetnum
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and
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.Fn cgetstr
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can be used to implement the traditional syntax and semantics of `#'
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and `='.
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Typeless capabilities are typically used to denote boolean objects with
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presence or absence indicating truth and false values respectively.
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This interpretation is conveniently represented by:
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.Pp
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.Dl "(getcap(buf, name, ':') != NULL)"
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.Pp
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A special capability,
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.Ic tc= name ,
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is used to indicate that the record specified by
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.Fa name
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should be substituted for the
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.Ic tc
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capability.
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.Ic Tc
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capabilities may interpolate records which also contain
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.Ic tc
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capabilities and more than one
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.Ic tc
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capability may be used in a record. A
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.Ic tc
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expansion scope (i.e., where the argument is searched for) contains the
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file in which the
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.Ic tc
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is declared and all subsequent files in the file array.
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.Pp
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When a database is searched for a capability record, the first matching
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record in the search is returned. When a record is scanned for a
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capability, the first matching capability is returned; the capability
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.Ic :nameT@:
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will hide any following definition of a value of type
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.Em T
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for
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.Fa name ;
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and the capability
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.Ic :name@:
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will prevent any following values of
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.Fa name
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from being seen.
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.Pp
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These features combined with
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.Ic tc
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capabilities can be used to generate variations of other databases and
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records by either adding new capabilities, overriding definitions with new
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definitions, or hiding following definitions via `@' capabilities.
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.Sh EXAMPLES
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.Bd -unfilled -offset indent
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example\||\|an example of binding multiple values to names:\e
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:foo%bar:foo^blah:foo@:\e
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:abc%xyz:abc^frap:abc$@:\e
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:tc=more:
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.Ed
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.Pp
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The capability foo has two values bound to it (bar of type `%' and blah of
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type `^') and any other value bindings are hidden. The capability abc
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also has two values bound but only a value of type `$' is prevented from
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being defined in the capability record more.
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.Pp
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.Bd -unfilled -offset indent
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file1:
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new\||\|new_record\||\|a modification of "old":\e
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:fript=bar:who-cares@:tc=old:blah:tc=extensions:
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file2:
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old\||\|old_record\||\|an old database record:\e
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:fript=foo:who-cares:glork#200:
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.Ed
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.Pp
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The records are extracted by calling
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.Fn cgetent
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with file1 preceding file2.
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In the capability record new in file1, fript=bar overrides the definition
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of fript=foo interpolated from the capability record old in file2,
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who-cares@ prevents the definition of any who-cares definitions in old
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from being seen, glork#200 is inherited from old, and blah and anything
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defined by the record extensions is added to those definitions in old.
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Note that the position of the fript=bar and who-cares@ definitions before
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tc=old is important here. If they were after, the definitions in old
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would take precedence.
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.Sh CGETNUM AND CGETSTR SYNTAX AND SEMANTICS
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Two types are predefined by
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.Fn cgetnum
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and
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.Fn cgetstr :
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.Bl -column "nameXnumber"
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.Sm off
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.It Em name No \&# Em number Ta numeric
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.Sm on
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capability
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.Em name
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has value
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.Em number
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.Sm off
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.It Em name No = Em string Ta "string capability"
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.Sm on
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.Em name
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has value
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.Em string
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.Sm off
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.It Em name No \&#@ Ta "the numeric capability"
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.Sm on
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.Em name
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does not exist
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.Sm off
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.It Em name No \&=@ Ta "the string capability"
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.Sm on
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.Em name
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does not exist
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.El
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.Pp
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Numeric capability values may be given in one of three numeric bases.
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If the number starts with either
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.Ql 0x
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or
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.Ql 0X
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it is interpreted as a hexadecimal number (both upper and lower case a-f
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may be used to denote the extended hexadecimal digits).
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Otherwise, if the number starts with a
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.Ql 0
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it is interpreted as an octal number.
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Otherwise the number is interpreted as a decimal number.
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.Pp
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String capability values may contain any character. Non-printable
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.Dv ASCII
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codes, new lines, and colons may be conveniently represented by the use
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of escape sequences:
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.Bl -column "\e\|X,X\e\|X" "(ASCII octal nnn)"
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^X ('X' & 037) control-X
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\e\|b, \e\|B (ASCII 010) backspace
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\e\|t, \e\|T (ASCII 011) tab
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\e\|n, \e\|N (ASCII 012) line feed (newline)
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\e\|f, \e\|F (ASCII 014) form feed
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\e\|r, \e\|R (ASCII 015) carriage return
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\e\|e, \e\|E (ASCII 027) escape
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\e\|c, \e\|C (:) colon
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\e\|\e (\e\|) back slash
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\e\|^ (^) caret
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\e\|nnn (ASCII octal nnn)
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.El
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.Pp
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A `\|\e' may be followed by up to three octal digits directly specifies
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the numeric code for a character. The use of
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.Tn ASCII
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.Dv NUL Ns s ,
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while easily
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encoded, causes all sorts of problems and must be used with care since
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.Dv NUL Ns s
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are typically used to denote the end of strings; many applications
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use `\e\|200' to represent a
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.Dv NUL .
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.Sh DIAGNOSTICS
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The
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.Fn cgetent ,
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.Fn cgetset ,
|
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.Fn cgetmatch ,
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.Fn cgetnum ,
|
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.Fn cgetstr ,
|
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.Fn cgetustr ,
|
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.Fn cgetfirst ,
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and
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.Fn cgetnext
|
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functions
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|
return a value greater than or equal to 0 on success and a value less
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than 0 on failure.
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The
|
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.Fn cgetcap
|
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function returns a character pointer on success and a
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.Dv NULL
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on failure.
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.Pp
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The
|
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.Fn cgetent ,
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and
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.Fn cgetseq
|
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functions may fail and set
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.Va errno
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for any of the errors specified for the library functions:
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.Xr fopen 3 ,
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|
.Xr fclose 3 ,
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.Xr open 2 ,
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and
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|
.Xr close 2 .
|
|
.Pp
|
|
The
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.Fn cgetent ,
|
|
.Fn cgetset ,
|
|
.Fn cgetstr ,
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and
|
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.Fn cgetustr
|
|
functions
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may fail and set
|
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.Va errno
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as follows:
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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No memory to allocate.
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.El
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.Sh SEE ALSO
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.Xr cap_mkdb 1 ,
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.Xr malloc 3
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.Sh BUGS
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Colons (`:') can't be used in names, types, or values.
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.Pp
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There are no checks for
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.Ic tc Ns = Ns Ic name
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loops in
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.Fn cgetent .
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.Pp
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The buffer added to the database by a call to
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.Fn cgetset
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is not unique to the database but is rather prepended to any database used.
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